{ "taxonomy": { "gasket_brief": "NUMBERS FIRST. 85A TPU compressive load (Texin 985, molded, ASTM D575): 0.345 / 1.03 / 2.07 / 3.10 / 4.31 / 5.52 / 16.5 MPa at 2 / 5 / 10 / 15 / 20 / 25 / 50 % deflection. I extracted these from the datasheet text myself and they match the gasket researcher: https://sushengpolymer.com/media/pdf/phFiH7_Texin-985.pdf . Same sheet: compression set (ASTM D395B / ISO 815) 16-19 % at 23 C/22 h and 40-80 % at 70 C/22 h; flexural modulus 26.9 MPa at 23 C vs 59.0 MPa at -30 C (2.2x). Printed-filament Ultrafuse TPU 85A: set 26 % (23 C/72 h) and 52 % (70 C/24 h), tear 80 kN/m flat vs 18-30 kN/m on edge/upright, break stress 34 vs 10 MPa (researcher-sourced, not re-checked by me): https://www.dream3d.co.uk/wp-content/uploads/2022/12/Ultrafuse_TPU_85A_TDS_EN_v2.5.pdf .\n\nLINE LOAD (own calculation = D575 stress x bead width; 3 x 3 mm bead has shape factor ~0.5, close to the D575 button's 0.57; treat as +/-2x for printed beads because fill pattern alone changed 100%-fill 85A peak force 1315 vs 2587 N, https://reference-global.com/2/v2/download/article/10.2478/aucts-2024-0004.pdf). Solid 3x3 mm bead: 4.1 N/mm at 6.7 % squeeze, 6.2 at 10 %, 9.3 at 15 %, 12.9 at 20 %, 16.6 at 25 %. On a 700 mm path (200x150 mm lid) that is 2.9 / 4.3 / 6.5 / 9.0 / 11.6 kN. Rule of thumb about 3.1-5.5 N/mm per mm of bead width at 15-25 %; an independent neo-Hookean check with E ~12 MPa (https://plahunter.pages.dev/data-sheets/ninjatek/tpu-ninjaflex) and shape factor gives 2-6 N/mm per mm width, i.e. within ~15-25 % of the datasheet curve. Narrow 1.2 x 2.4 mm rib: 1.7 N/mm at 7 % up to 5.2 N/mm at 20 % (Texin-scaled, conservative-high; my shape-factor correction gives ~3.9 N/mm at 20 %). 1 mm rigid rib pressed 1 mm into a flat 3 mm gasket: ~4-9 N/mm (rough, +/-2x). 3 mm round cord (Lindley, E ~14 MPa): 3.1 N/mm at 15 %, 4.8 at 20 %. Hollow or low-infill printed bead: assumed 0.3-0.6x solid, unmeasured.\n\nSEAL THRESHOLDS. Elastomers seal at about 1.4 MPa (200 psi) assembly stress, recommended minimum 4 MPa for 70A (Garlock, https://legacy.garlock.com/sites/default/files/documents/en/Gasket%20Assembly%20Stress%20Non-metallic%20-%20Aug%202022.pdf ); 1.4 MPa is only ~6.7 % squeeze on the Texin curve. IP67 water head is ~9.8 kPa (own calc), negligible, so leaks come from FDM surface roughness and layer-line paths, not pressure. Squeeze guidance: 20-30 % for solid rubber (Elasto Proxy https://www.elastoproxy.com/how-much-compression-do-rubber-gaskets-require/ , KRAIBURG https://www.kraiburg-tpe.com/pl/node/1281 ); Parker static max ~30 %, minimum 0.2 mm absolute squeeze, gland fill 60-85 % (https://nfc.arizona.edu/sites/default/files/2022-02/parker_o-ring_handbook.pdf ); about 10-12 % residual squeeze needed (https://www.nrc.gov/docs/ML1419/ML14195A258.pdf ).\n\nWHAT THIS MEANS FOR LATCHES. (1) Stroke is tiny: 0.20-0.75 mm for a 3 mm bead, the same order as FDM warp and hinge play, so every design needs a printed hard stop beside each latch (height ~0.75-0.8 x free bead) plus adjustability or a series spring. (2) Compression set: 52 % set at 70 C means a rigid fixed-travel latch loses ~30-58 % of its force after hot sun; a steel spring about 4x softer than the gasket cuts that to ~7-10 % (own calc: loss = set x ks/(kg+ks)). (3) Cold: modulus is 2.2x at -30 C, so closing force at fixed stroke may be 1.5-2x higher at -20 C. (4) Latch count is limited by rim bending, not latch strength: pitch L = (384 EI d / w)^0.25 with E = 1.8 GPa (assumed), bow d = 0.15 mm, w = 3.7 N/mm gives ~28 mm for a flat 3 mm lid edge, ~110 mm with a 20 mm skirt, ~154 mm with a 30 mm box rim (own calc); stiffen the rim before buying a stronger latch. (5) Recommended gasket: 2-4 N/mm line load (1.2-1.6 mm wide, >=2 mm tall rib, 20-25 % squeeze, printed flat at 100 % infill, ironed land, hard stops). Per-latch force then equals line load x latch pitch (e.g. 100 mm pitch = 200-400 N). Solid 3 mm beads at 15 %+ need >1 kN per latch on 6 latches and are beyond what any printed latch holds for months. Only printed-latch-plus-85A-TPU design found: MakerWorld Tough Case 2385298 (PETG snap latches, no force or IP data): https://www.makerworld.com/en/models/2385298 . No source certifies any printed TPU gasket to IP67.", "materials_brief": "TEMPERATURE. Black enclosure in direct sun reached 67.6 C inside (grey 51.4 C), informal hobby test: https://community.element14.com/challenges-projects/design-challenges/experimenting-with-extreme-environments/b/blog/posts/exploring-hidden-extremes-of-sheltered-environment---extra-blog-4--greenhouse-in-the-box . Design for 60-70 C surface.\n\nHEAT LIMITS (HDT at 1.8 MPa unless stated). ASA: Tg 97.8 C, HDT 100.2 C (Polymaker https://cdn.shopify.com/s/files/1/0603/6609/files/PolyLite_ASA_TDS_V5.1.pdf ); Bambu ASA HDT 92 C (snippet). PETG: HDT 68 C (Prusament https://cdn.shopify.com/s/files/1/1745/6181/files/PETG_TechSheet_ENG.pdf ), Polymaker PETG Tg 81 C, HDT 75 C. PETG-CF: Tg 68 C, HDT 68 C (74 C at 0.45 MPa) https://cdn.shopify.com/s/files/1/0380/5149/files/Bambu_PETG-CF_Technical_Data_Sheet.pdf , so carbon fibre does not fix PETG heat. PC (PolyMax): Tg 113 C, HDT 99-114 C. PA6-CF: HDT 173 C dry but Tg 74 C. PAHT-CF (PA12-type): HDT 170 C. Loaded oven test (CNC Kitchen): PLA fails ~65 C, PETG softens 80 C / fails ~85 C, ASA softens 110 / fails 120 C, PC Blend 110 / 125 C: https://cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament . A PETG latch at 60-70 C sits at or above its HDT: avoid for sustained load.\n\nCREEP (data are thin). Dogan 2022, 3 h tests on milled specimens: ABS ruptured in ~3 min at 60 C and 20 MPa; PLA broke at 60 C even at 10 MPa; PC never ruptured and crept least; nylon crept most without rupture: https://ojs30.sv-jme.eu/index.php/sv-jme/article/download/191/118/2454 . No ASA or PETG creep data beyond 3 h at 60 C exists in anything I found. Bolt-preload tests: M4 at 0.8 Nm, 1 week, room temp: ASA and PLA needed about one re-tighten, PA6 almost daily (https://www.cnckitchen.com/blog/carbon-fiber-nylon-in-3d-printing-pa6-vs-pa12-tested ); bolted PETG joints lost 11.5 % preload in 7 days vs 3 % PLA (https://filamentspecs.com/creep-resistance-3d-printed-parts/ ). Fibre grades rank PAHT-CF > PC > PLA for creep (https://link.springer.com/10.1007/s11665-024-09144-9 ). My working rule (own judgement; researchers disagreed: 5-8, 5-9 and <=3-5 MPa): sustained in-plane stress for ASA at 60-70 C of 3-5 MPa cautious, up to 5-8 MPa optimistic; bearing under steel pins/washers ~8-10 MPa; across layers ~2 MPa. Put preload in steel (spring, screw, insert).\n\nANISOTROPY. Hook tests (CNC Kitchen, same link): ASA lying 57 kg vs standing 17 kg (29 %), PETG 55 vs 25 kg (46 %), PLA 73 vs 40 kg; ASA in a 30 C chamber 20 kg (+20 %). PC Blend lying 74-77 kg vs standing 22-35 kg (https://www.cnckitchen.com/blog/prusament-pc-blend-review ). Datasheets claim ASA Z/XY tensile of 73-84 % (Polymaker 32/43.8 MPa; Bambu 31/37 MPa) but Z elongation only 1.65 %; hooks are far worse, so design to 29 %. Rule: lever, link, hook and bearing loads in the XY plane, pin axes along Z, 4+ perimeters, 0.2 mm layers or finer on a 0.4 mm nozzle.\n\nUV AND WEATHER. ASA -0.7 % yield and -3 % break stress after 1000 h QUV; unstabilised PC -34 % yield, dE 33 (strong yellowing); TPU 92A -15 %; nylon 12CF stable: https://stratasys.com/siteassets/abm-pages/aerospace/wp_fdm_uv-aging_a4_0123a.pdf . PETG UV results range +9 % (mild lamp, 100 h) to -36 % (UV-B), vendor/forum report yellowing and embrittlement at 6-12 months (https://pmc.ncbi.nlm.nih.gov/articles/PMC10146359/ , https://qidi3d.com/ja/blogs/print-lab/asa-petg-sprinkler-brackets-outdoor ). Field: original moulded pool-controller latches broke after ~10 years in sun (https://www.stlfinder.com/model/replacement-for-pentair-lxlatch-NuK4TAoL/5223236 ). Avoid unstabilised PP (months). Cold: injection-moulded ASA 3 kJ/m2 notched Charpy at -30 C, so no sharp internal corners; PC stays tough (snippet).\n\nMOISTURE AND NYLON. PA6-CF takes up 3.33 % water, XY strength -22 % and modulus -24 % after conditioning (https://cdn.shopify.com/s/files/1/0548/7299/7945/files/PolyMide_PA6_CF_TDS_V5.2.pdf ); PAHT-CF 0.88 %. Avoid PA6-CF outdoors; PAHT-CF acceptable but still creeps.\n\nWHAT CHANGES WITH OTHER MATERIALS. ASA is the default. PC (UV-stabilised grade only) gives the best heat and creep margin and probably raises sustained limits ~1.3-1.5x (own judgement, unmeasured). PETG and PETG-CF are marginal at 60-70 C. PA-CF mainly adds stiffness and heat margin, but moisture and nylon creep offset it.\n\nHARDWARE AND INTERFACES. Use A2/A4 stainless pins, screws and springs; zinc-plated steel 12-72 h salt spray, yellow zinc 96-120 h (https://www.albanycountyfasteners.com/media/48/29/31/1764608481/fastener-materials-and-coatings-guide.pdf ); music wire rusts and tops out ~121 C, 302/304 stainless spring ~288 C but 25-30 % weaker (https://www.leespring.com/music-wire-versus-stainless-steel ). M3 heat-set insert in PETG pulls out at 119 kg (~1.17 kN), torque-out 3 Nm; direct screw 118 kg but strips at 1 Nm; side-pocket nut 86 kg, bottom-pocket nut 166 kg (https://www.cnckitchen.com/blog/helicoils-threaded-insets-and-embedded-nuts-in-3d-prints-strength-amp-strength-assessment ); room-temperature peak values, not hot or sustained. Class 8.8 proof loads M3 2.92, M4 5.10, M5 8.23 kN (https://international.optimas.com/technical-resources/iso-metric-thread-proof-loads ), so the printed boss always limits.", "required_force": { "total_N_low": 1400, "total_N_high": 2800, "per_latch_N_at_4": 700, "per_latch_N_at_6": 467, "per_latch_N_at_8": 350, "basis": "Reference scenario: 200 x 150 mm lid, continuous gasket on a 700 mm path (own geometry, from the gasket researcher). The numbers are the closing force needed to hold the DESIGN gasket at end of life, not a solid wide bead. Low = 2 N/mm x 700 mm = 1.4 kN; high = 4 N/mm x 700 mm = 2.8 kN. The 2-4 N/mm window is a 1.2-1.6 mm wide, >=2 mm tall TPU 85A rib: at the Garlock seal stress of 1.4 MPa a 1.2 mm rib needs 1.7 N/mm, and at 20 % squeeze a 1.2 x 2.4 mm rib gives ~3.9 N/mm after my shape-factor correction (5.2 N/mm if you scale the Texin curve without it). per_latch values use the HIGH total (2.8 kN / 4, 6, 8); the low-end per-latch figure is exactly half (350 / 233 / 175 N). Rule: per-latch force = line load x latch pitch, so it scales with lid size. Sanity check: I extracted the Texin 985 ASTM D575 table from https://sushengpolymer.com/media/pdf/phFiH7_Texin-985.pdf (2/5/10/15/20/25/50 % = 0.345/1.03/2.07/3.10/4.31/5.52/16.5 MPa); the gasket researcher's arithmetic is correct, and an independent neo-Hookean estimate (E ~12 MPa, shape factor 0.5) lands within ~15-25 % of the curve. ALTERNATIVE (solid 3 x 3 mm bead, own calc): 2.9 kN at 6.7 % squeeze, 6.5 kN at 15 %, 11.6 kN at 25 % total; at 6 latches 483 / 1085 / 1932 N each, which exceeds any printed latch's sustained capacity (my estimates top out at ~300-800 N). Cross-sections: 3 mm round cord 2.2-5.0 kN; 1 mm rib into flat gasket 2.8-6.3 kN (rough). Corner and end latches may carry +20-30 % (assumption). A rigid fixed-travel latch must be preloaded 1.4-2.4x higher at assembly to still hold this load after 30-58 % force loss from 85A compression set at 70 C (Ultrafuse 52 % set), which is why adjustable or spring-loaded latches are favoured. Uncertainty +/-2x on printed-bead stiffness; verify with a force-gauge test on the actual printed bead." }, "mechanisms": [ { "id": "swing-bolt-wing-nut", "name": "Swing bolt / eye bolt with wing nut or knob in a printed clevis", "family": "rotary-screw", "description": "A steel M4-M6 swing bolt (DIN 444 style) pivots on a pin in a printed clevis, swings into a slot in the lid flange and is tightened with a wing nut or knob. Clamp force is the screw preload F = T/(K d), so force is continuously adjustable and re-tensionable, which is the best answer to TPU compression set. The steel bolt carries the tension; the weak points are the printed clevis ears (pin bearing) and the slot seat, so use a steel washer on the slot seat, pin axis along Z so the ears are loaded in-plane, and a hard stop beside the latch so hand torque cannot over-crush the gasket. Slower to operate than a lever; wing nut can back off with vibration (add a spring or nyloc element). Hand-tight easily exceeds the printed limit, so cap torque with a small knob.", "printability": "printed_plus_hardware", "hardware_needed": "M4-M5 stainless swing/eye bolt, wing nut or knob, steel washers, 4-5 mm stainless pivot pin; optional spring washer.", "evidence": "SUSTAINED (own est., ASA, SF~2): 300-800 N per latch (2 ears of 6-8 mm on a 4-5 mm pin at ~8-10 MPa bearing = ~380-720 N; higher with a steel clevis). PEAK: ~1.2-2 kN, set by ears or slot seat (own est.). PRELOAD (own calc, K=0.2): M5 at 1.5 Nm = 1.5 kN, M4 at 1 Nm = 1.25 kN, M3 at 0.5 Nm = 0.83 kN; class 8.8 proof loads M3 2.92, M4 5.10, M5 8.23, M6 11.6 kN https://international.optimas.com/technical-resources/iso-metric-thread-proof-loads . DIN 444 swing bolts exist in steel classes 4.6/5.6 (M5-M39) but no working-load table was found https://www.aspenfasteners.com/m5-0-8-x-35mm-din-444-type-b-metric-precision-swing-eye-bolts-steel . Bearing proxy: FDM ABS/PLA pin-lug coupons reached 189 MPa ultimate bearing, 3.6 kN fracture at W/D=3 (short term, search summary) https://mdpi.com/2073-4360/15/7/1660 . No test of a printed swing-bolt closure exists. CONFIDENCE: medium for the steel load path, low for the printed clevis.", "sources": [ { "title": "ISO metric thread proof loads (Optimas)", "url": "https://international.optimas.com/technical-resources/iso-metric-thread-proof-loads", "note": "class 8.8 proof loads M3-M6" }, { "title": "DIN 444 type B swing eye bolts (Aspen Fasteners)", "url": "https://www.aspenfasteners.com/m5-0-8-x-35mm-din-444-type-b-metric-precision-swing-eye-bolts-steel", "note": "dimensions and steel classes only; no load table" }, { "title": "Pin-bearing strength of AM polymer parts (Polymers 2023)", "url": "https://mdpi.com/2073-4360/15/7/1660", "note": "values from search summary; page 403 on fetch" } ] }, { "id": "cam-lever-steel-stud", "name": "Eccentric cam clamping lever on a steel stud with steel contact plate", "family": "cam-lever", "description": "A lever with an eccentric cam bears on a steel plate and tensions a threaded stud, giving about 19-21:1 amplification of hand force (Ganter GN 927 principle). The setting nut or stud length sets preload, and the clamp stays on after release. Printable as lever plus cam with a steel M4-M6 stud, steel pivot pin and a hardened washer or steel insert in the cam path, because a printed cam face flat-spots and creeps under months of load. The pivot pin carries the full stud tension, so the printed lever ears set the limit. Print with pin axis along Z so cam, ears and lever lie in the XY plane. Friction plastic/steel ~0.15 helps holding but lets the cam creep; needs a detent against vibration.", "printability": "printed_plus_hardware", "hardware_needed": "M4-M6 stainless stud and nut, stainless pivot pin 4-5 mm, steel washer or contact plate, optional steel cam insert and detent.", "evidence": "SUSTAINED (own est., ASA): 300-700 N (pivot bearing ceiling: M4 pin x 2x6 mm ears ~380-480 N; M5 pin x 2x8 mm ~720 N, own calc at 8-10 MPa). PEAK: ~2-3x sustained (own est.). STEEL REFERENCE, verified by me on the Elesa page: GN 927.2 manual force 75 N gives 1450 N (size 44), 125 N gives 2600 N (63), 200 N gives 4300 N (82), 350 N gives 7000 N (101); recommended safety factors 1.2-1.5 static, 1.8-2.4 pulsating, 3-4 alternating; friction coefficients plastic/steel 0.15, plastic/plastic 0.25, steel/steel 0.2 https://elesa.com/en/elesab2bstoreca/Clamping-handles--Cam-levers--GN9272-A--d1 . Family 'up to 8 kN' https://ctemag.com/?p=107957 ; ELESA metal cam clamp LAC.44 3500 N max https://docs.rs-online.com/df90/A700000013422799.pdf . No printed cam-lever force test found by any researcher. CONFIDENCE: medium (steel path) / low (printed lever).", "sources": [ { "title": "Elesa GN 927.2 cam levers", "url": "https://elesa.com/en/elesab2bstoreca/Clamping-handles--Cam-levers--GN9272-A--d1", "note": "clamping force table, safety factors and friction coefficients verified by lead" }, { "title": "GN 927.7 clamping levers (CTE Magazine)", "url": "https://ctemag.com/?p=107957", "note": "up to 8 kN" }, { "title": "ELESA cam clamp datasheet (RS)", "url": "https://docs.rs-online.com/df90/A700000013422799.pdf", "note": "LAC.44 3500 N; via search summary" } ] }, { "id": "baseline-screws", "name": "Baseline: lid screws into heat-set inserts or captive nuts", "family": "rotary-screw", "description": "Not a quick latch but the strength baseline every latch should beat on force. A steel M3-M5 screw with washer pulls the lid into a brass heat-set insert (or captive nut in a bottom pocket) in a printed boss; the steel is never the weak link, the boss and washer bearing area are. Preload is torque-controlled and re-tightenable, and creeps away over days to weeks in printed plastics, so use a metal washer or sleeve (compression limiter) and plan a re-tighten after the first hot cycle. Slow, needs a tool. Insert interface: 4 perimeters, 100 % infill around the boss, hole sized per insert maker. Combines well with a hard stop. Includes the direct-screw, captive-nut, Helicoil and through-bolt variants.", "printability": "printed_plus_hardware", "hardware_needed": "M3-M4 stainless screws, brass heat-set inserts (Ruthex-type) or nuts, washers, optional metal compression-limiter sleeves.", "evidence": "SUSTAINED (own est.): 300-500 N per M3/M4 screw with washer (30-50 mm2 bearing at ~10 MPa); SF 2 on the PETG M3 insert peak gives ~580 N at 23 C before any hot derate (own calc). PEAK: ~1.2 kN (insert pull-out). MEASURED (CNC Kitchen, PETG M3, flat bar, 4 perimeters, 100 % infill, n=3): Ruthex insert 119 kg (~1.17 kN) pull-out, 3 Nm torque-out; direct screw 118 kg but 1 Nm strip torque; Helicoil 120 kg; side-pocket nut 86 kg (~840 N); bottom-pocket nut ~166 kg (~1.63 kN) https://www.cnckitchen.com/blog/helicoils-threaded-insets-and-embedded-nuts-in-3d-prints-strength-amp-strength-assessment . PLA M3: Ruthex 181 kg, eBay insert 157 kg, cheap moulded insert 39 kg https://www.cnckitchen.com/blog/threaded-inserts-for-3d-prints-cheap-vs-expensive . Hole sweep: ~1.4 kN average at 3.6 mm hole in PLA https://www.cnckitchen.com/blog/are-our-heat-set-insert-datasheets-wrong . M4 bolt creep, 1 week at room temp: ASA and PLA ~1 re-tighten https://www.cnckitchen.com/blog/carbon-fiber-nylon-in-3d-printing-pa6-vs-pa12-tested ; PETG joints lost 11.5 % preload in 7 days https://filamentspecs.com/creep-resistance-3d-printed-parts/ . Printed lid layers split under bolt clamping (PLA instrument housing) https://hackaday.io/project/12125/log/41900 . Insert white paper (provenance unclear) M3/M4/M5 1.3/2.7/3.4 kN, low confidence. No hot (60-70 C) or sustained data. CONFIDENCE: medium at 23 C, low when hot.", "sources": [ { "title": "CNC Kitchen: helicoils, threaded inserts and embedded nuts (PETG M3)", "url": "https://www.cnckitchen.com/blog/helicoils-threaded-insets-and-embedded-nuts-in-3d-prints-strength-amp-strength-assessment", "note": "pull-out and torque-out values" }, { "title": "CNC Kitchen: threaded inserts cheap vs expensive (PLA M3)", "url": "https://www.cnckitchen.com/blog/threaded-inserts-for-3d-prints-cheap-vs-expensive", "note": "181/157/39 kg" }, { "title": "CNC Kitchen: carbon fiber nylon PA6 vs PA12 (bolt creep)", "url": "https://www.cnckitchen.com/blog/carbon-fiber-nylon-in-3d-printing-pa6-vs-pa12-tested", "note": "M4 bolt creep test, 1 week" }, { "title": "filamentspecs: creep resistance of 3D printed parts", "url": "https://filamentspecs.com/creep-resistance-3d-printed-parts/", "note": "PETG 11.5 % vs PLA 3 % preload loss in 7 days" } ] }, { "id": "captive-screw-spring-stack", "name": "Captive stainless screw clamp with spring or Belleville stack and metal insert", "family": "rotary-screw", "description": "A captive stainless M4/M5 thumbscrew or knob pulls the lid through a heat-set insert, with a coil spring or disc-spring stack (or a longer screw with a hardened spacer) under the head. The spring is chosen about 4x softer than the gasket, so a few hundredths of a millimetre of plastic creep or gasket set barely changes preload. This is the reference creep-tolerant clamp: the load path is steel, only the boss, washer seat and flange are plastic. Needs travel about 4x the gasket squeeze, a hard stop and a captive retainer so the screw is not lost outdoors. Disc springs help less than hoped in thermally cycled, creeping joints, so test.", "printability": "printed_plus_hardware", "hardware_needed": "A4 stainless screw or thumbscrew, heat-set insert, stainless coil spring or Belleville stack, hardened washer or spacer sleeve, retainer clip.", "evidence": "SUSTAINED (own est.): 300-500 N, same printed boss and washer seat limit as baseline-screws, but retains most of the preload. PEAK ~1.2 kN. PRELOAD RETENTION (own calc): loss fraction = set x ks/(kg+ks); with ks = kg/4 loss is 0.2 x set = 7-10 % for 35-52 % TPU set, against 35-52 % for a rigid joint https://sushengpolymer.com/media/pdf/yKRdOr_Elastollan-C85A55.pdf . Plastic joints lose clamp load as thickness is lost to creep; metal inserts do not creep https://uk.spirol.com/assets/files/ins-wp-how-to-maintain-joint-integrity-when-converting-from-metal-to-plastic-us.pdf . A vendor white paper claims Belleville washers cut loss below 1 % in steel joints (vendor claim, not validated for plastic) https://www.solonmfg.com/documents/Combatting%20Embedment%20Relaxation%20in%20Bolted%20Joints%20-February%202025%20Final%20Version.pdf ; ASME PVP2008 says springs or longer bolts reduce load loss in flange joints https://www.sciencegate.app/document/10.1115/pvp2008-61005 . Forum advice: smaller fastener plus hardened spacer adds compliance https://eng-tips.com/threads/calculation-of-the-stiffness-of-a-plastic-member-in-a-bolted-joint.502550/latest . Gasket stiffness basis: 3x3 mm bead at 15 % is ~2.4 kN/mm per 117 mm latch share. No printed-host test. CONFIDENCE: medium-low.", "sources": [ { "title": "SPIROL: maintaining joint integrity converting metal to plastic", "url": "https://uk.spirol.com/assets/files/ins-wp-how-to-maintain-joint-integrity-when-converting-from-metal-to-plastic-us.pdf", "note": "creep loses clamp load; metal inserts do not creep" }, { "title": "Solon: combatting embedment relaxation in bolted joints", "url": "https://www.solonmfg.com/documents/Combatting%20Embedment%20Relaxation%20in%20Bolted%20Joints%20-February%202025%20Final%20Version.pdf", "note": "vendor claim, steel joints" }, { "title": "ASME PVP 2008: Belleville washers to reduce relaxation", "url": "https://www.sciencegate.app/document/10.1115/pvp2008-61005", "note": "flange context, metal" }, { "title": "Elastollan C85A55 datasheet (TPU 85A compression set)", "url": "https://sushengpolymer.com/media/pdf/yKRdOr_Elastollan-C85A55.pdf", "note": "25 % at 23 C and 35 % at 70 C, used in the preload-loss calc" } ] }, { "id": "vise-action-screw-cam", "name": "Vise-action / lift-and-turn compression latch (cam plus screw take-up)", "family": "rotary-screw", "description": "A T-handle or lift-and-turn handle rotates a cam behind the frame and a screw or cam rise draws the panel toward the frame by a defined travel (Southco N4, E3, M1, 62 series). Southco states NEMA 4 / IP65-66 when used with the supplied flange or cup gasket. Printable analogue: printed handle and cam turning a steel M4/M5 screw through a heat-set insert or captive nut, drawing a printed hook against the frame; preload adjustable and the load path is the steel screw. Limits: the printed hook/bridge and cam seat creep; screw preload at hand torque (M4 at 1.5 Nm ~1.9 kN, own calc) far exceeds what printed seats hold, so a torque-limiting feature or hard stop is needed. Commercial bodies are zinc or aluminium, which do not transfer.", "printability": "mostly_hardware", "hardware_needed": "M4-M5 stainless screw, heat-set insert or captive nut, steel washer, optional wave spring; or buy the commercial latch.", "evidence": "SUSTAINED (own est., printed analogue): 200-500 N; PEAK ~700-1200 N. COMMERCIAL (static, not sustained): Southco N4 600 N max working load, 1200 N average ultimate, 300 N average compression force on the frame https://docs.rs-online.com/eca8/0900766b801e0b3a.pdf ; E3 large 450 N adjustable grip / 300 N fixed grip (stainless 600/450 N) https://datasheets.globalspec.com/ds/southco/e3-16-206/829690b1-1f4e-4eab-b06d-1ffb2d2929cb ; M1-20 460 N short cam / 350 N long cam, M1-25 1010 / 350 N, NEMA 4/IP66 with flange gasket https://media.southco.com/media/static/Literature/m1-c.en.pdf ; 62 series 220 N small, 440-670 N medium, 1250 N large flush https://static.datasheets.com/doc/8464620-southco-62-10-23-rs-ds.pdf . Insert not limiting: M3 in PETG 1.17 kN https://www.cnckitchen.com/blog/helicoils-threaded-insets-and-embedded-nuts-in-3d-prints-strength-amp-strength-assessment . Most of these ratings come from search-result text. CONFIDENCE: medium for commercial numbers, low for the printed analogue.", "sources": [ { "title": "Southco N4 datasheet (RS)", "url": "https://docs.rs-online.com/eca8/0900766b801e0b3a.pdf", "note": "600 N working, 1200 N ultimate, 300 N compression; via search text" }, { "title": "Southco E3-16-206 (GlobalSpec)", "url": "https://datasheets.globalspec.com/ds/southco/e3-16-206/829690b1-1f4e-4eab-b06d-1ffb2d2929cb", "note": "450/300 N static; via search text" }, { "title": "Southco M1 literature", "url": "https://media.southco.com/media/static/Literature/m1-c.en.pdf", "note": "NEMA 4/IP66 with flange gasket" }, { "title": "Southco 62 datasheet", "url": "https://static.datasheets.com/doc/8464620-southco-62-10-23-rs-ds.pdf", "note": "static loads 220-1250 N" } ] }, { "id": "quarter-turn-compression", "name": "Quarter-turn compression latch (steel cam and ramp, 4-6 mm draw-down)", "family": "rotary-screw", "description": "A quarter turn engages a cam behind the panel and a ramp or screw draws the door 4-6 mm against the gasket (EMKA 1000, Southco E9, Essentra). EMKA: first 90 degree turn positions the latch on a 3 mm ramp, the second adds ~5.5-6 mm compression; sealing is designed around PUR foam gaskets. A printed version uses a printed knob and ramp on a steel shaft with nut and washers, ideally with a steel or hardened cam, because printed helical ramps wear and creep. Mismatch with 85A TPU: 6 mm of travel against a bead needing 0.2-0.75 mm means the ramp must either end in a hard stop or the force depends on where the ramp parks, so ramp geometry (steeper = lower force) and a stop decide preload. Mount in a panel cutout.", "printability": "printed_plus_hardware", "hardware_needed": "Steel shaft or screw, nut, washers, optionally a metal cam; panel cutout and key or tool drive.", "evidence": "SUSTAINED (own est., printed knob/ramp on steel shaft): 150-400 N; PEAK ~500-1000 N. COMMERCIAL: Essentra zinc quarter-turn compression lock 562 N max load at 6 mm compression, -50 to +80 C https://www.digikey.cn/htmldatasheets/production/2905106/0/0/1/compression-cam-latch-datasheet.pdf (search text); EMKA 1000-U805 verified by me: 6 mm compression, IP65, PUR foamed gasket, no load rating given https://www.emka.com/products/1000-u805 ; EMKA second stage ~5.5 mm https://www.electronicspecifier.com/?p=113370 ; Southco E9 ~4 mm, IP66/IP67 https://southco.com/en_gb_int/e9-a005f-02 . All ratings assume foam gaskets (EMI low-closure gaskets are ~0.2-1.4 N/mm vs 85A TPU 4-12 N/mm). No printed pull-off test. Orientation: ramp faces in the XY plane. CONFIDENCE: low-medium.", "sources": [ { "title": "EMKA 1000-U805 compression latch", "url": "https://www.emka.com/products/1000-u805", "note": "6 mm compression, IP65, PUR foam; no force rating (verified by lead)" }, { "title": "ElectronicSpecifier: EMKA compression latch", "url": "https://www.electronicspecifier.com/?p=113370", "note": "5.5 mm direct pull plus 3 mm ramp" }, { "title": "Essentra compression cam latch datasheet (DigiKey)", "url": "https://www.digikey.cn/htmldatasheets/production/2905106/0/0/1/compression-cam-latch-datasheet.pdf", "note": "562 N at 6 mm; via search text" }, { "title": "Southco E9-A005F-02", "url": "https://southco.com/en_gb_int/e9-a005f-02", "note": "4 mm compression, IP66/IP67; via search text" } ] }, { "id": "oc-adjustable-screw-hook", "name": "Over-center draw latch with steel threaded adjuster (re-tensionable hook)", "family": "over-center", "description": "Printed lever and base pivot on steel pins; the hook is a steel eye-bolt, M4-M5 screw with lock nut, or steel hook with a threaded link in a heat-set insert or metal nut. Over-center lock holds without friction, and the screw lets the user trim travel to the 0.2-0.75 mm a 3 mm TPU bead needs and re-tension after compression set. The printed hook root is removed from the load path, so printed pivots and base set the limit. Commercial analogue: Southco E8 (7.9 mm adjustment, GF nylon, stainless nut) and the metal Ganter/Camloc/DE-STA-CO latches. Pair with a hard stop so over-tightening cannot crush the gasket. Pin axes along Z, lever in XY.", "printability": "printed_plus_hardware", "hardware_needed": "Stainless eye-bolt or M4-M5 screw, lock nut, steel hook or keeper, 3-4 mm stainless pivot pins, heat-set insert; optional spring.", "evidence": "SUSTAINED (own est., ASA): 150-300 N; PEAK ~500-900 N. PLASTIC BENCHMARK: Southco E8 1560 N max working load, -29 to 80 C, ~7.9 mm adjustment https://southco.com/en_gb_int/E8 and https://pdf.nauticexpo.com/pdf/southco/e8-adjustable-style-draw-latches/22514-91220.html (search text). STEEL (not printable): Ganter GN 850-500 5000 N, GN 853-160 1750 N, GN 851-160 1600 N (https://www.ehorst.de/en/Verschluss-Spanner-mit-Zuganker-GN-850-1-500-TG-mit-Gegenhalter-1398999.html ); Kipp K0080 1800 N traction (https://www.marek.eu/data/katalogove-listy/kipp/K0080.pdf ); Misumi 1630 N (https://my.misumi-ec.com/vona2/detail/110310215549/ ); DE-STA-CO 331 700 lbf (~3.1 kN) https://destaco.com/productdetails.331.html , 341 2000 lbf (~8.9 kN) https://destaco.com/productdetails.341.html ; Camloc working load is 0.5-0.67 of max (95L 220/445 N) https://efc-intl.com/printitems/metal-access-fasteners/camloc-95l-series-tension-draw-latches ; Ganter notes vibration and shock reduce holding capacity. Patent: threaded link is in compression when latched https://patents.justia.com/patent/4540206 . Ideal toggle gain 1/(2 tan theta): ~14:1 at 2 deg, ~5.7:1 at 5 deg (own calc; the Firgelli page I fetched gives no such formula and says real force depends on geometry and stiffness). Insert pull-out is not limiting (M3 PETG 1.17 kN). No printed sustained test. CONFIDENCE: low-medium.", "sources": [ { "title": "Southco E8 adjustable draw latches", "url": "https://southco.com/en_gb_int/E8", "note": "1560 N working load; via search text, page 403" }, { "title": "Camloc 95L (EFC)", "url": "https://efc-intl.com/printitems/metal-access-fasteners/camloc-95l-series-tension-draw-latches", "note": "220 N working vs 445 N max" }, { "title": "DESTACO 331 / 341", "url": "https://destaco.com/productdetails.341.html", "note": "2000 lbf; 331 is 700 lbf" }, { "title": "Ganter GN 850-500 (ehorst)", "url": "https://www.ehorst.de/en/Verschluss-Spanner-mit-Zuganker-GN-850-1-500-TG-mit-Gegenhalter-1398999.html", "note": "5000 N holding force" }, { "title": "Adjustable draw latch US 4540206", "url": "https://patents.justia.com/patent/4540206", "note": "threaded link in compression when latched" } ] }, { "id": "threaded-lid-cap", "name": "Threaded closure (printed screw cap or threaded ring) with end-face TPU ring", "family": "rotary-screw", "description": "A large trapezoidal or buttress thread on a round lid or ring compresses a TPU ring on its end face; force is torque divided by thread lead and friction. One cap is the whole closure (no latch count). Threads alone do not seal (helical leak path), so seal on the end face. Round enclosures only. Orientation cannot be favourable all round: with the axis along Z the thread flanks bend across layers and peel at the roots; a horizontal thread is better but not fully; 45 degrees was strongest for ASA nuts. Line load from hand torque is low, which suits a light gasket only.", "printability": "fully_printed", "hardware_needed": "None; TPU end-face ring (95A worked well in one design, designers prefer a rubber O-ring over printed TPU).", "evidence": "SUSTAINED (own est., whole cap, low confidence): 100-300 N total axial; PEAK ~450-730 N. AXIAL FROM TORQUE (own calc): 50 mm cap, 4 mm lead, 2 / 3 / 4 Nm gives ~250-370 / 380-550 / 510-730 N for mu 0.3-0.2, which is only ~1.6-4.6 N/mm on a 157 mm circumference. TESTS: PETG 1/2-20 specimens split at the outer wall at ~100-110 lbf (~450-490 N) per thread, anecdotal https://3dprintingspace.com/t/thread-strength-testing/7351 ; PLA+ 1/4-20 pulled at 48 lbf (10 % infill), 68 (25 %), 90 (50 %), >110 lbf (100 %), reader-reported https://hackaday.com/2023/11/10/putting-3d-printed-screw-threads-to-the-test ; printed cap split along layers under bolt force https://hackaday.io/project/12125/log/41900 ; helical gap leaks https://forums.autodesk.com/t5/fusion-design-validate-document/water-tight-threads-not-working-correctly/m-p/11662111 ; ASA nut study (abstract) https://www.mmscience.eu/journal/issues/june-2025/articles/analysis-of-3d-printed-metric-nuts-manufactured-by-the-mex-method-from-asa-material ; sealed screw container with TPU 95A https://printables.com/model/1233019-container-sealable-screwable-scaleable-strong-3-ve ; one study found printed connectors <30 % of expected clamping force (exact page not pinned down) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9781732/ . CONFIDENCE: low.", "sources": [ { "title": "Hackaday: putting printed screw threads to the test", "url": "https://hackaday.com/2023/11/10/putting-3d-printed-screw-threads-to-the-test", "note": "commenter pull-out figures by infill" }, { "title": "3D Printing Space: thread strength testing", "url": "https://3dprintingspace.com/t/thread-strength-testing/7351", "note": "PETG 1/2-20 forum test" }, { "title": "Hackaday.io: printed cap splits under bolt force", "url": "https://hackaday.io/project/12125/log/41900", "note": "layer splitting" }, { "title": "MM Science: 3D printed metric nuts in ASA", "url": "https://www.mmscience.eu/journal/issues/june-2025/articles/analysis-of-3d-printed-metric-nuts-manufactured-by-the-mex-method-from-asa-material", "note": "abstract only; 45 degrees strongest" }, { "title": "Printables: sealable screwable container", "url": "https://printables.com/model/1233019-container-sealable-screwable-scaleable-strong-3-ve", "note": "TPU 95A gasket" } ] }, { "id": "wedge-slide-bolt", "name": "Wedge / slide-bolt latch (tapered wedge into tapered catch)", "family": "wedge-slide", "description": "A sliding tapered bolt is pushed into a tapered catch, converting a hand push into a high axial pull; a 1:10 taper gives a mechanical advantage of about 10 before friction (own calc). It self-locks if the taper half-angle is below the friction angle: 1:10 is ~5.7 deg versus arctan(0.25) = 14 deg for plastic on plastic, so it holds without a detent. Prints well flat with the wedge faces in the XY plane, so it is fully printable with no hardware, and preload is set by wedge position (stepped or screw-driven for fine control). Risks: creep of the wedge faces, fretting, and loss of preload as TPU sets; a steel insert on the wedge face or a screw-driven wedge helps. Principle only; no source describes a gasket-sealing printed wedge latch.", "printability": "fully_printed", "hardware_needed": "Optional spring detent and steel insert on the wedge face.", "evidence": "SUSTAINED (own est., 10 mm wide ASA wedge): 100-300 N; PEAK ~400-900 N. NO PUBLISHED LOAD DATA FOUND. Friction coefficients used (plastic/plastic 0.25, plastic/steel 0.15) are from the Elesa page I verified https://elesa.com/en/elesab2bstoreca/Clamping-handles--Cam-levers--GN9272-A--d1 . The Firgelli toggle-latch page cited by the industrial researcher as wedge background does not mention wedges, so I do not rely on it. The web-search budget ran out before I could source a wedge latch. CONFIDENCE: low (reasoning only).", "sources": [ { "title": "Elesa GN 927.2 page (friction coefficients only)", "url": "https://elesa.com/en/elesab2bstoreca/Clamping-handles--Cam-levers--GN9272-A--d1", "note": "plastic/plastic 0.25, plastic/steel 0.15; no wedge latch source found" } ] }, { "id": "oc-fixed-hook-pinned", "name": "Over-center draw latch, printed body, steel pivot pins, fixed hook", "family": "over-center", "description": "Printed lever, link and base pivot on 3 mm (or M4) stainless pins; the hook is a printed hook or a bent stainless-wire hook with fixed take-up. The lever passes dead centre so it locks without friction. Clamp force is set by geometry (hook stretch x frame and gasket stiffness), not hand force. Print with pivot axes along Z and lever, link and hook in the XY plane, and never load a hook root across layers (ASA keeps 29 % of flat strength). A ~2 mm TPU pad between hook and mating side stabilises force (MakerWorld 1054989). Fixed travel means a rigid latch loses 30-58 % of its preload as 85A TPU takes set at 70 C, so add a hard stop and prefer the adjustable or spring variants.", "printability": "printed_plus_hardware", "hardware_needed": "2-3 stainless 3 mm pins or M3/M4 shoulder screws, optional bent stainless wire hook, ~2 mm TPU support pad.", "evidence": "SUSTAINED (own est., ASA, SF~2): 120-250 N (maker estimate from 3 mm pin bearing ~3x6 mm per wall; industrial estimate 100-300 N; reconciled). PEAK (own est.): 400-900 N. PLASTIC-BODY BENCHMARKS: Southco 37 lever-assist (GF nylon, stainless pins) 350 N clamping force, top variant 475 N (Marek) or 520 N (other listings, sources disagree), -40 to 80 C https://static.chipdip.ru/lib/031/DOC015031575.pdf and https://www.marek.eu/katalog-obrazku/produkt-8066/66871-37-l-en.pdf ; injection-moulded 30 % GF nylon is several times stronger than printed ASA. PRINTED EVIDENCE: MakerWorld Draw Latch survived ~42 lb (~187 N) without breaking but stretched out of position (lower bound, PLA-class, one anecdote) https://makerworld.com/en/models/2266330-draw-latch ; M3 toggle latch claims >10 kg https://www.stlfinder.com/model/m3-toggle-latch-high-performance-wkO8uZca/4063366 ; MakerWorld 1054989 has 3 mm steel and stainless pins and a 2 mm TPU pad, no force values https://makerworld.com/en/models/1054989-self-locking-toggle-latch . HOOK PROXY (CNC Kitchen): ASA hook lying 57 kg vs standing 17 kg; SF 2 gives ~280 N lying and ~83 N standing, for that test geometry only https://cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament . Designers report failure by screw tearing out of the housing and say wall count matters more than infill. CONFIDENCE: low-medium.", "sources": [ { "title": "Southco 37 series datasheet copy", "url": "https://static.chipdip.ru/lib/031/DOC015031575.pdf", "note": "350 N heavy-duty clamping force" }, { "title": "Southco 37 catalogue (Marek)", "url": "https://www.marek.eu/katalog-obrazku/produkt-8066/66871-37-l-en.pdf", "note": "475 N top variant" }, { "title": "MakerWorld Draw Latch 2266330", "url": "https://makerworld.com/en/models/2266330-draw-latch", "note": "42 lb test; via search text, page 403" }, { "title": "MakerWorld Self-Locking Toggle Latch 1054989", "url": "https://makerworld.com/en/models/1054989-self-locking-toggle-latch", "note": "steel pins and 2 mm TPU pad; no force values" }, { "title": "CNC Kitchen: comparing PLA, PETG and ASA hooks", "url": "https://cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament", "note": "hook lying vs standing" }, { "title": "M3 toggle latch (STLFinder)", "url": "https://www.stlfinder.com/model/m3-toggle-latch-high-performance-wkO8uZca/4063366", "note": ">10 kg claim" } ] }, { "id": "oc-spring-loaded-compensating", "name": "Spring-backed over-center latch (steel spring in series; stored-energy or ratchet-stop gasket compensating)", "family": "over-center", "description": "A printed lever and hook on stainless pins, with the closing load passing through a stainless coil spring, disc stack or spring-steel hook in series with the gasket. The spring is much softer than the gasket, so compression set, thermal movement and plastic creep change preload only slightly. Variants: spring over-center that stores energy and pulls the lid in once past the balance point; spring-biased floating carriage with a toothed or ramped stop that follows an aging gasket; self-compensating spring-steel drawhook. Needs travel of about 4x the gasket squeeze (~3 mm for 0.75 mm) and a hard stop. Spring must be stainless (302/304/316) because music wire rusts; a printed flexure instead of steel loses at least ~14 % per 1000 h and far more when hot.", "printability": "printed_plus_hardware", "hardware_needed": "Stainless compression/torsion spring or Belleville stack, 3-4 mm stainless pins, printed ratchet teeth optional.", "evidence": "SUSTAINED (own est., ASA lever and pins limit): 100-250 N, with preload retained to within ~7-10 % of set-induced loss instead of 35-58 %. PEAK ~400-800 N. PRELOAD MODEL (own calc): loss = set x ks/(kg+ks); a 3x3 mm bead at 15 % squeeze has a secant stiffness of ~20.7 N/mm per mm length per mm stroke, ~2.4 kN/mm for one latch's 117 mm share; a printed hook of 200-1000 N/mm (assumed) is 2.4-12x softer, so 0.1 mm of drift moves force ~20-100 N rather than ~240 N. PATENTS (no force values): ITW gasket-compensating latch with spring-biased carriage and toothed stop https://patents.justia.com/patent/8376418 ; stored-energy over-center latch https://patents.google.com/patent/US9370294 ; Camloc self-compensating spring-steel drawhook listing https://www.scribd.com/doc/109459302/Camloc-Ram-h . COMMERCIAL: Southco flexible over-center lever latch 350 N clamp (snippet) https://southco.com/en_au_int/latches/compression-latches/lever-latches/a2a7-over-center-lever-latches . Creep reference: injection-moulded PC creep modulus 2200 to 1900 MPa from 1 h to 1000 h at 23 C https://www.okw.ch/it/PC/RW_Makrolon_2405_en.pdf ; spring materials https://www.leespring.com/music-wire-versus-stainless-steel . No printed test exists. CONFIDENCE: low-medium.", "sources": [ { "title": "Gasket-compensating latch mechanism US 8376418 (ITW)", "url": "https://patents.justia.com/patent/8376418", "note": "spring-biased carriage, toothed stop" }, { "title": "Stored energy gasket-compressing latch US 9370294", "url": "https://patents.google.com/patent/US9370294", "note": "based on search summary" }, { "title": "Camloc catalogue excerpt (Scribd)", "url": "https://www.scribd.com/doc/109459302/Camloc-Ram-h", "note": "self-compensating spring-steel drawhook line" }, { "title": "Southco A2/A7 over-center lever latches", "url": "https://southco.com/en_au_int/latches/compression-latches/lever-latches/a2a7-over-center-lever-latches", "note": "350 N, EPDM, stainless pins; page 403, from snippet" }, { "title": "Makrolon 2405 datasheet", "url": "https://www.okw.ch/it/PC/RW_Makrolon_2405_en.pdf", "note": "creep modulus 2200 to 1900 MPa" }, { "title": "Music wire versus stainless steel (Lee Spring)", "url": "https://www.leespring.com/music-wire-versus-stainless-steel", "note": "temperature and strength" } ] }, { "id": "bayonet-twist-lock", "name": "Bayonet / twist-lock lid with ramps", "family": "rotary-screw", "description": "Lugs on the lid slide under ramps on the body; turning climbs the ramps and compresses the gasket axially; steeper ramps give less force. One lid is the whole closure. Fully printable, round or squarish small lids only; lug shear and ramp face orientation dominate (print the lid upside-down so lugs are in-plane, solid top and bottom layers, ASA or PETG). It needs a notch or detent so it cannot rotate back, because vibration can unwind a bayonet. Ramp creep and wear lose preload; a steel pin or metal ramp insert helps.", "printability": "fully_printed", "hardware_needed": "None required; optional metal detent pin or spring.", "evidence": "SUSTAINED (own est., whole lid, low confidence): 50-300 N (maker estimate 50-150 N shared over ~3 lugs; industrial estimate 150-300 N); PEAK 300-600 N. RAMP CALC (own): F = T/(r tan(alpha+phi)); T 2 Nm, r 25 mm, ramp 3/5/10 deg, mu 0.2 gives ~314/273/205 N; mu 0.3 gives ~223/201/159 N. EVIDENCE: heavy-duty two-lug MakerWorld bayonet lid in PETG, designer reports months outdoors (search text) https://makerworld.com/models/1924555 ; bayonet pill box closes in about 1/8 turn, claims 10 cm for 10 min, warns under-extruded seal leaks (search text) https://www.stlfinder.com/model/customizable-waterproof-pill-box-FhdEExnI/2424312 ; Wikipedia, which I fetched, confirms the lock relies on pegs, slots and a spring or detent and can fail if pegs break or the spring weakens https://en.wikipedia.org/wiki/Bayonet_mount . No pull-off or torque tests found. CONFIDENCE: low.", "sources": [ { "title": "MakerWorld heavy-duty bayonet lid", "url": "https://makerworld.com/models/1924555", "note": "printed upside-down, PETG, outdoor months; via search text" }, { "title": "Customizable Waterproof Pill Box (stlfinder)", "url": "https://www.stlfinder.com/model/customizable-waterproof-pill-box-FhdEExnI/2424312", "note": "1/8 turn bayonet, 10 cm/10 min claim" }, { "title": "Wikipedia: Bayonet mount", "url": "https://en.wikipedia.org/wiki/Bayonet_mount", "note": "principle; peg, slot and spring failure modes (fetched by lead)" } ] }, { "id": "cam-hook-printed", "name": "Printed cam-lever hook latch (zx82net / cam-latch-for-boxes style)", "family": "cam-lever", "description": "Two-part printed latch: a cam lever on a pivot pin hooks a catch and the cam throw pulls the lid down onto the seal; designer says a cam latch applies significant static pressure to the TPU seal versus a simple clip. Essentially a simplified over-center hook with a printed pin: load path is a printed hook arm (tension plus bending) and printed pivot, so hook root and pivot creep limit it. Use M3/M4 screw or steel-pin pivots, ASA, 100 % infill in the moving part, and print the arm on its side so layers lie in the plane of the arm. The cam contact creeps, so it can back off under vibration; add a steel cam shaft, bushing and detent if used outdoors.", "printability": "printed_plus_hardware", "hardware_needed": "M3/M4 screws and nuts or heat-set inserts as pivots, optional steel pivot pin, TPU gasket.", "evidence": "SUSTAINED (own est., ASA, M4 pivots): 60-150 N (maker 60-150 N; industrial 50-200 N); PEAK 250-600 N. No force or pull-off test published. SEAL TEST: reviewer submerged zx82net box 10 cm for 10 min, dry with thick seal, ~10 ml in with thin seal https://www.myminifactory.com/object/3d-print-zx82net-customizable-rugged-waterproof-box-146437 ; designer recommends PETG over PLA because PLA creeps and loosens the seal https://www.thingiverse.com/thing:3338826 ; MakerWorld Waterproof Box (cam latch, printed TPU seal or silicone, 8x M3x20, 3 perimeters >30 % infill, tested in PLA/PETG only) https://makerworld.com/en/models/454290-waterproof-box ; Printables cam latch for boxes: 100 % infill on moving latch part, locking arms break first https://www.printables.com/model/355435-cam-latch-for-boxes ; stronger-cam remix https://makerworld.com/en/models/87535-cam-latch-for-boxes . Same family: Instructables/MakerWorld printed toggle clamps and cam F clamps (no force data). CONFIDENCE: low.", "sources": [ { "title": "zx82net Customizable Rugged Waterproof Box (MyMiniFactory)", "url": "https://www.myminifactory.com/object/3d-print-zx82net-customizable-rugged-waterproof-box-146437", "note": "cam latch, TPU or cord seal, leak test" }, { "title": "zx82net box (Thingiverse 3338826)", "url": "https://www.thingiverse.com/thing:3338826", "note": "PLA creep warning; via search text" }, { "title": "MakerWorld Waterproof Box 454290", "url": "https://makerworld.com/en/models/454290-waterproof-box", "note": "cam latch plus TPU seal; perimeters and infill advice" }, { "title": "Cam latch for boxes (Printables)", "url": "https://www.printables.com/model/355435-cam-latch-for-boxes", "note": "M4 mounting, 100 % infill on latch" } ] }, { "id": "perimeter-band-clamp", "name": "Perimeter band clamp (V-band / Marman / flange clip clamp / strap buckle band)", "family": "other", "description": "A band, strap or hinged halves tension around mating flanges; a V-groove wedge converts band tension into axial clamp force through the wedge angle and friction, spreading load evenly round the perimeter and avoiding point loading of the gasket. Needs matching round or oval flanges. Printed as segmented halves or flange clips with a steel T-bolt or over-center closure; the tension member should be steel or reinforced because wedge faces and webbing creep and UV-age. Blue Robotics prototyped BlueROV2 end-cap clips in print at about 2x the size of the aluminium ones and they worked.", "printability": "printed_plus_hardware", "hardware_needed": "Steel band or T-bolt, over-center latch or buckle, printed V-ring or flange clips; stainless threaded rod where used.", "evidence": "SUSTAINED (own est., total axial per closure, low confidence): a few hundred N, up to ~1 kN with a steel band; per-latch comparison not meaningful. No printed V-band load numbers exist. THEORY: axial load rises with band pretension and with friction, and ultimate-capacity models tended to over-predict (Huddersfield) https://eprints.hud.ac.uk/id/eprint/22987/1/eng-2015-0010.pdf , https://pure.hud.ac.uk/en/publications/axial-load-capacity-of-v-section-band-clamp-joints/ . ANECDOTES: Blue Robotics printed clips https://discuss.bluerobotics.com/t/enclosure-clips/2854 ; MakerWorld bistable strap lock https://makerworld.com/ja/models/463867-quick-release-strap-locks-with-loop-retention , ASA D-ring buckle https://makerworld.com/en/models/674852-double-d-ring-buckle-strap , Field Repair Buckle https://www.printables.com/model/1247230-field-repair-buckle . CONFIDENCE: low.", "sources": [ { "title": "Barrans et al., Open Engineering 2015: V-band axial load", "url": "https://eprints.hud.ac.uk/id/eprint/22987/1/eng-2015-0010.pdf", "note": "pretension and friction; via search summary" }, { "title": "Axial load capacity of V-section band clamp joints", "url": "https://pure.hud.ac.uk/en/publications/axial-load-capacity-of-v-section-band-clamp-joints/", "note": "load prediction with friction" }, { "title": "Blue Robotics forum: enclosure clips", "url": "https://discuss.bluerobotics.com/t/enclosure-clips/2854", "note": "printed clips about 2x aluminium size worked" }, { "title": "MakerWorld quick-release strap locks", "url": "https://makerworld.com/ja/models/463867-quick-release-strap-locks-with-loop-retention", "note": "bistable cam strap lock; no force data" } ] }, { "id": "oc-fully-printed", "name": "Fully printed over-center draw latch (assembled hooks-over-pivots or print-in-place)", "family": "over-center", "description": "Lever, link and hook are printed with no steel pivots, either assembled with hooks over printed pivots or print-in-place. Cheap and quick, but layer-bonded printed pivots with clearance gaps creep and wear, so it only gives light preload. Fine for splash-proof boxes with soft gaskets; marginal for solid 85A TPU. Printed with thick walls (about 1.2 mm per wall class), ASA or PC, link and hook on their sides. Includes the Pentair LXLATCH-style reprints and sturdy print-in-place draw latches.", "printability": "fully_printed", "hardware_needed": "None; optional 3 mm steel pins to harden pivots.", "evidence": "SUSTAINED (own est., ASA): assembled 40-100 N, print-in-place 25-60 N, sturdy PIP 15-40 N; PEAK 100-400 N. EVIDENCE: Draw Latch 2266330 survived ~187 N (lower bound) https://makerworld.com/en/models/2266330-draw-latch ; print-in-place latch box 2435156, 5 mm walls, splash-proof without gasket, 'almost waterproof' with TPU 95A, no test data https://makerworld.com/models/2435156 ; Sturdy PIP draw latch, designer says weaker than metal latches https://www.printables.com/model/130254-sturdy-print-in-place-draw-latch ; wider reinforced-mount version https://www.printables.com/model/1388482-wider-sturdy-latch-with-optional-reinforced-mount ; Pentair replacement: original moulded latches broke after ~10 years in sun, reprint in ABS/PETG/PC https://www.stlfinder.com/model/replacement-for-pentair-lxlatch-NuK4TAoL/5223236 . CONFIDENCE: low.", "sources": [ { "title": "MakerWorld Draw Latch 2266330", "url": "https://makerworld.com/en/models/2266330-draw-latch", "note": "187 N lower bound" }, { "title": "MakerWorld Waterproof Latch Sealed Boxes - Print-in-Place", "url": "https://makerworld.com/models/2435156", "note": "via search text" }, { "title": "Sturdy print-in-place draw latch (Printables)", "url": "https://www.printables.com/model/130254-sturdy-print-in-place-draw-latch", "note": "drawbacks section: not sturdy vs metal latches" }, { "title": "Replacement for Pentair LXLATCH (stlfinder)", "url": "https://www.stlfinder.com/model/replacement-for-pentair-lxlatch-NuK4TAoL/5223236", "note": "original broke after about a decade in sun" } ] }, { "id": "bail-wire-latch", "name": "Stainless wire bail latch with printed retainers", "family": "over-center", "description": "A bent 304/316 stainless wire acts as both spring and hook; printed parts only hold the wire ends and form the over-center cam seat or catch. The elastic energy is stored in steel, which shows negligible creep at 60-70 C, so preload is more stable than any printed spring. Stainless stores less energy than music wire (275-300 ksi vs >400 ksi), so use larger wire. Force is normally low (jar-clamp class). Design principle, not a documented gasket latch; the printed catch seat can still creep.", "printability": "printed_plus_hardware", "hardware_needed": "1.6-3 mm 304/316 stainless spring wire, printed wire holders and catch.", "evidence": "SUSTAINED (own rough est., low confidence): ~20-100 N for 2-3 mm wire; panel-clip class with 1.6 mm wire ~5-20 N. PEAK not estimated. No load rating found for bail or wire latches. MATERIALS: 302/304 stainless to ~288-316 C, music wire only to ~121 C and rusts https://www.leespring.com/music-wire-versus-stainless-steel . PRINTED EXAMPLES: spring-wire panel latch with 1.6 mm wire, tension-bar depth 2 mm PLA / 2.5 mm ASA, works in white ASA (3dgo mirror, search text) https://3dgo.app/models/printables/1395495 ; print-in-place panel latch https://printables.com/model/1042802-sturdy-print-in-place-panel-latch-for-2020-extrusi . CONFIDENCE: low.", "sources": [ { "title": "Music wire versus stainless steel (Lee Spring)", "url": "https://www.leespring.com/music-wire-versus-stainless-steel", "note": "temperature and strength of wire materials" }, { "title": "Steel-wire panel latch (Printables 1395495 via 3dgo)", "url": "https://3dgo.app/models/printables/1395495", "note": "1.6 mm wire; 2 / 2.5 mm tension bar PLA / ASA; page 403, from search text" }, { "title": "Sturdy print-in-place panel latch (Printables 1042802)", "url": "https://printables.com/model/1042802-sturdy-print-in-place-panel-latch-for-2020-extrusi", "note": "lead only" } ] }, { "id": "rotary-cam-lock-simple", "name": "Rotary cam lock / tapered quarter-turn latch with little or no draw-down", "family": "rotary-screw", "description": "A quarter-turn cam or tapered tongue engages behind the frame; plain versions give no defined compression, a roller cam gives up to 2 mm, and the printed tapered design compresses lightly via a taper. Easily printed on a steel shaft, but the cam sees line contact and creeps, and travel and force are too low for solid 85A TPU. Use for dust or splash with foam or thin lip gaskets, or as a secondary lock.", "printability": "printed_plus_hardware", "hardware_needed": "Steel shaft or screw and nut; optional key/tool drive.", "evidence": "SUSTAINED (own est.): printed 20-60 N, steel-shaft cam <100 N; PEAK 100-250 N. EVIDENCE: Southco E5 roller cam up to 2 mm compression, Flush Cup accessory NEMA 4/IP65 https://brandspurng.com/2020/09/23/southco-introduces-new-product-extensions-to-its-successful-e5-cam-latch-series/ ; MakerWorld quarter-turn latch (compression capable): 4 printed parts, 90 degree turn, taper compression, 2.5 mm acrylic default panel, no force data https://makerworld.com/models/3070853 ; E5 316 stainless cam latch 670 N rating is for the metal part (via Gripwell/Southco sheet, search text). CONFIDENCE: low.", "sources": [ { "title": "Southco E5 cam latch extensions", "url": "https://brandspurng.com/2020/09/23/southco-introduces-new-product-extensions-to-its-successful-e5-cam-latch-series/", "note": "roller cam up to 2 mm; Flush Cup NEMA 4/IP65" }, { "title": "MakerWorld Quarter-turn latch (compression capable)", "url": "https://makerworld.com/models/3070853", "note": "printed taper compression; via search summary" } ] }, { "id": "multi-point-rod-latch", "name": "Multi-point rod latch (handle drives rods or bellcranks to top and bottom latch points)", "family": "other", "description": "A single handle drives rods or cables to several latch points around the door, spreading gasket compression over the perimeter instead of loading one point. Used on gasket-sealed outdoor cabinets with large door spans. Force per point is no higher than one compression latch. A printed bellcrank linkage creeps and develops backlash, and the rods and guides are usually steel, so only the housings and guides are printable. Does not fit the small 70x35x30 mm envelope; its value is spreading load on large lids, together with a stiff rim.", "printability": "mostly_hardware", "hardware_needed": "Steel rods, guides, latch points and handle; printed housings, bellcranks and guides.", "evidence": "SUSTAINED per point: no published rating; same order as a single compression latch (several hundred N, per industrial researcher). No numbers found. Qualitative: multi-point latching recommended for large door spans https://www.magazine-industry-usa.com/news/1936-getting-the-latch-and-hinge-specification-right ; marketed for gasket-sealed outdoor use (search text) https://www.globalspec.com/ds/3851/areaspec/features_gasket . CONFIDENCE: very low.", "sources": [ { "title": "Magazine Industry USA: getting the latch and hinge specification right", "url": "https://www.magazine-industry-usa.com/news/1936-getting-the-latch-and-hinge-specification-right", "note": "qualitative; no numbers" }, { "title": "GlobalSpec: gasket latches", "url": "https://www.globalspec.com/ds/3851/areaspec/features_gasket", "note": "multi-point latch marketed for gasket-sealed outdoor use; search text" } ] }, { "id": "snap-fit-compliant", "name": "Snap-fit cantilever hook and compliant catches (incl. press-and-pull and TPU strap latches)", "family": "snap-compliant", "description": "A printed flexing arm hooks over a ledge (also spring-loaded press-and-pull hooks like Pelican, bistable snap-through locks, and TPU/EPDM strap latches stretched over a catch). Free, quick and print-in-place, but it holds by elastic deflection, so it cannot generate or maintain gasket preload and it relaxes under sustained strain and heat. Print the arm flat so bending runs along the roads; design strain about 3 % flat and half standing for PETG/ABS/ASA (design rule, not measured). Use only as alignment or secondary retention beside a proper clamp or with a hard stop.", "printability": "fully_printed", "hardware_needed": "None; optional steel spring for press-and-pull.", "evidence": "SUSTAINED (own est.): snap-fit 10-30 N per catch, TPU strap latch ~20-100 N once relaxed; PEAK 40-120 N snap, TPU strap 49-176 N new. MEASURED: ABS cantilever hooks (16 geometries) retention 1.7 to ~41 N, insertion ~3-34 N https://journal.ump.edu.my/ijame/article/view/11091 ; strain rules https://buildcad.ai/snap-fit-3d-printing ; Southco EPDM flexible latch 49 N, -20 to 95 C and Gripwell C7 49-176 N https://www.gripwell.com.sg/image/catalog/Gripwell/Engineered Access Hardware/Latches/Draw Latches/C7 Flexible Draw Latch/Gripwell - C7 Flexible Draw Latch.pdf ; Pelican Storm iM2435: PBT latch plus EPDM O-ring, no force published https://www.pelican.com/us/en/product/cases/iM2435/pdf ; MakerWorld Tough Case 2385298 pairs PETG snap latches with a TPU 85A gasket, no force or IP data https://www.makerworld.com/en/models/2385298 ; zx82net snap closure https://www.printables.com/model/59227-zx82net-ultimate-parametric-rugged-box-snap-closur ; Thingiverse clip-latch rugged box with filament pins, PLA+ 15 % infill, no test https://harktech.co.uk/m/thingiverse/7208214 . Not suitable for solid 85A TPU. CONFIDENCE: medium for the ranking, low for numbers.", "sources": [ { "title": "Analyzing insertion and retention forces in cantilever snap-fits (IJAME 2025)", "url": "https://journal.ump.edu.my/ijame/article/view/11091", "note": "ABS, abstract values 1.7-41 N" }, { "title": "buildcad.ai snap-fit calculator", "url": "https://buildcad.ai/snap-fit-3d-printing", "note": "strain design assumptions, not measurements" }, { "title": "Gripwell C7 flexible draw latch", "url": "https://www.gripwell.com.sg/image/catalog/Gripwell/Engineered Access Hardware/Latches/Draw Latches/C7 Flexible Draw Latch/Gripwell - C7 Flexible Draw Latch.pdf", "note": "49 N small / 176 N large; search text" }, { "title": "Pelican Storm iM2435 spec sheet", "url": "https://www.pelican.com/us/en/product/cases/iM2435/pdf", "note": "PBT latch, EPDM O-ring, no force values" }, { "title": "MakerWorld Rugged Waterproof Tough Case 2385298", "url": "https://www.makerworld.com/en/models/2385298", "note": "TPU 85A gasket plus PETG snap latches; no data" } ] }, { "id": "double-throw-butterfly", "name": "Double-throw / butterfly recessed case latch (stamped steel)", "family": "other", "description": "A spring-loaded folding lever locks into a catch with a double-throw action, used on flight cases. Cheap and proven but built from 1.2 mm stamped steel for lid weight and shock, not gasket compression; closing force is set by fixed geometry with little adjustment. Only the principle transfers; a flat printed version is poorly suited because it depends on sheet-steel spring and thin hooks. Use as a secondary keeper, not as the primary clamp for 85A TPU. Note: the Penn Elcom page I fetched calls it a butterfly latch and does not use the words double-throw, so the label is the researchers', not verified.", "printability": "mostly_hardware", "hardware_needed": "Buy stamped steel latch and catch; printed recess and keeper only.", "evidence": "COMMERCIAL: Penn Elcom medium MOL recessed butterfly latch L905 series, 90 kg (~880 N) maximum working load, 1.2 mm steel, zinc finish, verified by me https://translations.penn-elcom.com/medium-mol-recessed-latch-with-padlock-bracket-in-deep-dish-l905-928pbz . No printed estimate; the sustained force of a printed copy was not estimated and is expected to be low. CONFIDENCE: low.", "sources": [ { "title": "Penn Elcom medium MOL recessed latch L905/928PBZ", "url": "https://translations.penn-elcom.com/medium-mol-recessed-latch-with-padlock-bracket-in-deep-dish-l905-928pbz", "note": "90 kg working load; 1.2 mm steel; no double-throw wording (verified by lead)" } ] } ], "excluded": [ { "name": "Steel over-center draw latches (Southco 97, Bossard BN 32753, Camloc, Ganter GN 850/851/853, Kipp K0080, Misumi, DE-STA-CO 331/341)", "reason": "Not 3D-printable; used as force benchmarks only (Southco 97 135-670 N https://www.gripwell.com.sg/image/catalog/Gripwell/Furniture and Architectural Hardware/Latches/Draw Latches/97 Over-Center Draw Latch/Gripwell - 97 Over-Center Draw Latch.pdf ; Bossard 260-530 N https://www.bossard.com/pl-pl/eshop/zatrzaski-naciagowe/draw-latches-over-center-small-clamping-force-260-n-530-n-with-spring-loaded-anchor-plate-hole-for-wire-sealing/p/32753/ ; steel toggle latches 1.6-8.9 kN). Practical upgrade path is a bought stainless latch on printed bosses with through-bolts and metal backing washers, where the printed mount limits (~300-600 N, maker own est.)." }, { "name": "Hold-down / push-pull toggle clamps and printed F-clamp / cam F-clamp / toggle clamps (MakerWorld 2747558, 2616812, 2902106; Instructables linear toggle clamp)", "reason": "Merged into the over-center and cam-lever entries. Same toggle principle, but the geometry needs space above the lid and is too bulky for the 70x35x30 mm envelope; none is designed around a gasket and none publishes a force. Steel ratings for scale only: Misumi hold-down 196-264 N stainless, 1000-2270 N steel; push-pull 910-3860 N (https://th.misumi-ec.com/en/vona2/detail/110310211769 , https://th.misumi-ec.com/en/vona2/detail/221005335113 )." }, { "name": "Magnetic catch (printed carrier with neodymium magnet)", "reason": "Dropped as a clamp: 30 N retaining (cabinet catch) to ~89 N (K&J 20 lb) pull at contact against thick steel, and a gasket gap cuts it sharply; 85A TPU needs several times more. Only useful as an alignment keeper or closure indicator (https://www.kjmagnetics.com/ml-l-y0-magnetic-latches-for-cabinets-doors-drawers )." }, { "name": "Press-and-pull latch (Pelican Storm style)", "reason": "Merged into snap-fit-compliant. Pelican designs it for an EPDM O-ring needing low closing force; no force published (PBT latch)." }, { "name": "Flexible elastomeric TPU/EPDM strap latch and compliant/bistable print-in-place snap lock", "reason": "Merged into snap-fit-compliant. Elastic relaxation and compression set lose preload; 49-176 N new, snap-through tens of N." }, { "name": "Sturdy print-in-place draw latch, print-in-place latch box, assembled printed draw latch, Pentair LXLATCH reprints", "reason": "Merged into oc-fully-printed (same working principle and force class)." }, { "name": "Steel-pin-reinforced printed toggle latch (MakerWorld 1054989), engineered.at spoke-pin box, hook-and-catch / hasp printed hook", "reason": "Merged into oc-fixed-hook-pinned and cam-hook-printed; the hook-and-catch is a load-path component, not a separate mechanism. Hook test numbers are kept as evidence." }, { "name": "Engineered-plastic draw latches as separate entries (Southco E8, Southco 37 lever-assist)", "reason": "Merged as commercial benchmarks into oc-adjustable-screw-hook and oc-fixed-hook-pinned (E8 is adjustable, 37 is fixed lever-assist)." }, { "name": "Fastener interfaces: heat-set inserts, direct self-tapping screws, captive nut pockets, Helicoil, integral printed threads, pin-through-lug, through-bolt clamping", "reason": "Not mechanisms, but load interfaces. Folded into baseline-screws, swing-bolt-wing-nut, captive-screw-spring-stack and threaded-lid-cap as evidence (Helicoil gave no advantage over screw-in-plastic in PETG: 120 vs 118 kg)." }, { "name": "Gasket-side measures: positive compression stops, adjustable preload, compliant element in series, rib-into-flat gasket, solid bead, narrow rib, hollow gasket, round cord, tongue-and-groove gland, stiffened rim", "reason": "Not latches. Used in gasket_brief and required_force and as design requirements on the latches (hard stop beside each latch, adjustability or series spring, stiff rim). Note the internal tension that the gasket researcher's 2-4 N/mm target and 20-25 % squeeze only coincide for a narrow ~1.2 mm rib." }, { "name": "Design practices: metal-pin load path, added joint compliance (longer thinner fastener), re-tension after bedding-in, metal insert for mounting screws, ASA hardware selection", "reason": "Practices, not mechanisms; merged into the relevant entries and materials_brief." }, { "name": "Epoxy-bonded latch casing test (UW Midsun) and Blue Robotics clip anecdote as stand-alone items", "reason": "The epoxy test measures the adhesive bond (PETG 82 lb), not the latch; the clip anecdote is merged into perimeter-band-clamp." }, { "name": "Rotary claw-and-striker latch and ratchet pull-in latch as stand-alone entries", "reason": "Completeness gap I could not close. The web-search budget was exhausted when I tried to source them (all five completeness searches were refused), and Southco's rotary-latch page returned HTTP 403. The ratchet-stop and stored-energy variants are covered through the ITW patents inside oc-spring-loaded-compensating; the claw-and-striker latch needs a follow-up search before it can be ranked. Likewise no search could be run for wedge latches, so wedge-slide-bolt rests on reasoning only." }, { "name": "Unsupported source claims removed", "reason": "The Firgelli toggle-latch page does not give the 1/(2 tan) gain or support 'clamp force = stretch x spring rate' (it says real force depends on geometry and stiffness) and does not mention wedges; the toggle gain is therefore labelled my own calculation. The Penn Elcom page does not say 'double-throw'. The Texin sheet and Elesa GN 927.2 table were verified directly." } ] }, "sweep_key_facts": [ { "key": "industrial", "summary": "Survey of latch families for gasketed, IP-rated enclosures, with published ratings and a printability assessment against the reference conditions (one latch, FDM, 0.4 mm nozzle, about 70x35x30 mm, ASA or PETG, 60-70 C surface temperature in sun).\n\n1. Published numbers are mostly \"max static / working load\" and are not sustained clamp force. Commercial plastic-body latches (Southco GF-nylon) rate 350-475 N draw force (lever-assist) up to 1560 N working load (E8 over-center). Zinc compression latches rate 300-1010 N static. Steel latch clamps rate 1.6-19 kN. Manufacturer working load is about 0.5-0.67 of ultimate (Camloc, Southco N4).\n\n2. The central finding is the load the gasket asks for. Commercial compression latches (4-6 mm draw-down, about 300 N) are specified for foam or low-force gaskets. EMKA uses PUR foam. EMI low-closure-force gaskets are quoted at roughly 0.2-1.4 N/mm. My own estimate for a solid 85A TPU bead (E about 12 MPa) is about 2-6 N/mm per mm of width at 15-25 % compression, so about 4-12 N/mm for a 2 mm bead. That is roughly 10x or more what foam needs. 85A TPU also takes 26-52 % compression set at 70 C (BASF Ultrafuse 85A datasheet, via the dream3d.co.uk copy; ISO 815), so a rigid fixed-travel latch loses much of its preload. Prefer a spring-loaded or re-tensionable latch, a thin or hollow gasket profile, and a stiff flange.\n\n3. For printed parts, my own engineering estimate is about 100-400 N sustained per latch in ASA, from 5-8 MPa sustained design stress. Peak is 2-4x that. PETG (HDT about 68 C) is marginal at 60-70 C surface temperature. ASA (Tg about 108 C, HDT about 91-98 C) is the safer outdoor choice. ASA layer adhesion is weak (29 % of in-plane strength in CNC Kitchen's hook test), so orient every load path in-plane.\n\n4. Ranking of mechanisms by sustained force a printed version can plausibly deliver (my estimate): (a) swing bolt or eye bolt with wing nut, or captive screw with heat-set insert; (b) eccentric cam clamping lever with steel stud (GN 927 principle, about 20:1 mechanical advantage); (c) adjustable over-center hook latch with steel pins and a spring or adjusting screw; (d) cam-plus-screw compression latch; (e) screw-cap closure on round enclosures; (f) bayonet; (g) TPU strap, snap-fit and magnet, which are all unsuitable for 85A seals.\n\n5. Gaps. The shared WebSearch budget ran out partway through, and Southco, Penn Elcom, Essentra, Printables and MakerWorld pages returned HTTP 403, so Southco and Essentra figures come from distributor sheets or search snippets rather than primary datasheets. PDFs could not be parsed (no pdftotext). No published load ratings were found for Protex, Pinet, Fastenal, bail or wire latches, wedge latches, or multi-point rod latches. No sourced mechanical data was gathered for PC, PA6-CF or PETG-CF beyond retailer HDT tables. All printed-part sustained-force figures and gasket line loads in this report are my own estimates and should be verified by coupon pull tests. Treat the gasket line loads in particular as plus or minus 2x.", "key_facts": [ { "topic": "Manufacturer rating convention", "fact": "Manufacturer working load is about half to two thirds of ultimate. Camloc 95L: 220 N working vs 445 N max tensile; V934L 310/550 N; 1429L 1000/1500 N; V46L 3000/4500 N. Southco N4: 600 N working vs 1200 N average ultimate. McMaster defines 'capacity' as the maximum (peak) force the latch can withstand.", "value": "working = 0.5-0.67 x ultimate", "source_url": "https://efc-intl.com/printitems/metal-access-fasteners/camloc-95l-series-tension-draw-latches" }, { "topic": "Southco N4 compression force", "fact": "Southco N4 vise-action latch: maximum working load 600 N (136 lbf), average ultimate 1200 N, and average compression force of 300 N applied to the frame when the T-handle is turned. This is the clearest published 'gasket draw-down force' figure found.", "value": "300 N compression / 600 N working / 1200 N ultimate", "source_url": "https://docs.rs-online.com/eca8/0900766b801e0b3a.pdf" }, { "topic": "Southco E3 ratings", "fact": "E3 large vise-action compression latch: maximum static load 450 N (100 lbf) adjustable grip and 300 N (67 lbf) fixed grip; stainless/high-pressure sealed variants 600/450 N. NEMA 4/IP65 sealing with the supplied gasket. Mounting nut torque 20 Nm.", "value": "300-450 N static (600 N stainless)", "source_url": "https://datasheets.globalspec.com/ds/southco/e3-16-206/829690b1-1f4e-4eab-b06d-1ffb2d2929cb" }, { "topic": "Southco M1 ratings", "fact": "M1 lift-and-turn latches: M1-20 460 N (short cam) and 350 N (long cam); M1-25 1010 N (short cam) and 350 N (long cam). NEMA 4/IP66 sealing achieved with the supplied flange gasket.", "value": "350-1010 N static", "source_url": "https://media.southco.com/media/static/Literature/m1-c.en.pdf" }, { "topic": "Southco 62 series loads", "fact": "62 lift-and-turn latch static loads: 220 N small, about 440-670 N medium, 1250 N large flush. Required panel thickness is door thickness + 7 mm (+0.4 mm with cup gasket).", "value": "220-1250 N", "source_url": "https://static.datasheets.com/doc/8464620-southco-62-10-23-rs-ds.pdf" }, { "topic": "Draw-down travel of compression latches", "fact": "EMKA 1000 series compression latches pull the door about 6 mm against the gasket (first 90 degree turn positions on a 3 mm ramp, second turn adds about 5.5 mm), IP65, with a PUR foamed gasket; Southco E9 gives about 4 mm compression (IP66/IP67); Essentra offers 4 mm or 6 mm preset; Southco E5 roller cam up to 2 mm.", "value": "2-6 mm draw-down", "source_url": "https://www.electronicspecifier.com/?p=113370" }, { "topic": "Essentra compression latch load", "fact": "Essentra quarter-turn compression lock (zinc housing and driver, steel cam, rubber gasket): max load capacity 562 N at 6 mm compression, working range -50 to +80 C.", "value": "562 N", "source_url": "https://www.digikey.cn/htmldatasheets/production/2905106/0/0/1/compression-cam-latch-datasheet.pdf" }, { "topic": "Engineered-plastic draw latch loads", "fact": "Southco E8 adjustable over-center draw latch (acetal and glass-reinforced nylon, stainless adjusting nut): max working load 1560 N (350 lbf), -29 to 80 C, 7.9 mm adjustment. Southco 37 lever-assist heavy duty (GF nylon body, stainless pins): 350 N (79 lbf) clamping force, -40 to 80 C; top variant 475-520 N (sources disagree).", "value": "350-520 N clamp; 1560 N working (E8)", "source_url": "https://southco.com/en_gb_int/E8" }, { "topic": "Elastomeric draw latch force", "fact": "Southco EPDM flexible draw latch: 49 N average clamping force, -20 to 95 C. Gripwell C7 (TPE latch, GF nylon links): 49 N small, 176 N large.", "value": "49-176 N", "source_url": "https://www.gripwell.com.sg/image/catalog/Gripwell/Engineered Access Hardware/Latches/Draw Latches/C7 Flexible Draw Latch/Gripwell - C7 Flexible Draw Latch.pdf" }, { "topic": "Metal latch clamps", "fact": "DE-STA-CO pull-action latch clamps: 331 holds 700 lbf (about 3.1 kN, 1.75 in draw); 341 holds 2000 lbf (about 8.9 kN, 2.5 in draw). Ganter GN 850-500 5000 N; GN 853-160 1750 N; GN 851-160 1600 N; Kipp K0080 1800 N traction; Misumi latch type 1630 N.", "value": "1.6-8.9 kN (steel)", "source_url": "https://destaco.com/productdetails.341.html" }, { "topic": "Ganter vibration derating", "fact": "Ganter toggle latch datasheet notes that holding capacity can be adversely affected by conditions of use such as vibration or shock loads.", "value": "holding capacity derated by vibration/shock", "source_url": "https://toolteam.com/sv-SE/ganter-latch-type-toggle-clamps-for-pulling-action-850-1-500-tf-t-982861-4045525537026" }, { "topic": "Eccentric cam lever amplification", "fact": "Ganter GN 927.2 steel eccentric cam levers: 75 N hand force gives 1450 N (size 44), 125 N gives 2600 N (63), 200 N gives 4300 N (82), 350 N gives 7000 N (101). Ratio about 19-21:1. Recommended safety factors 1.2-1.5 static, 1.8-2.4 pulsating, 3-4 alternating. Friction coefficient plastic/steel about 0.15, steel/steel 0.2.", "value": "about 20:1 amplification", "source_url": "https://elesa.com/en/elesab2bstoreca/Clamping-handles--Cam-levers--GN9272-A--d1" }, { "topic": "Ideal toggle mechanical advantage", "fact": "[own calculation] Ideal rigid toggle gain = 1/(2*tan(theta)) past dead centre: about 14:1 at 2 degrees, 5.7:1 at 5 degrees, 3.6:1 at 8 degrees; the sources note real clamps are limited by friction and frame flex and that formulas disagree (tan vs sin forms).", "value": "1/(2 tan theta)", "source_url": "https://www.firgelliauto.com/blogs/mechanisms/toggle-latch" }, { "topic": "Swing bolt / screw clamp force", "fact": "[own calculation] Preload F=T/(K*d), K=0.2: M5 at 1.5 Nm gives about 1.5 kN; M4 at 1 Nm about 1.25 kN; M3 at 0.5 Nm about 0.83 kN. Class 8.8 proof loads: M3 2.92 kN, M4 5.10 kN, M5 8.23 kN, M6 11.6 kN. Printed seats, not the steel, limit the load.", "value": "M4/M5 hand-tight about 1.2-1.5 kN", "source_url": "https://international.optimas.com/technical-resources/iso-metric-thread-proof-loads" }, { "topic": "Heat-set insert pull-out", "fact": "M3 Ruthex heat-set insert in PETG (4 perimeters, 100 % infill): ripped out at 119 kg average (about 1170 N); torque-out 3 Nm; a bolt screwed directly into printed PETG failed at about 1 Nm.", "value": "119 kg (about 1170 N); 3 Nm", "source_url": "https://www.cnckitchen.com/blog/helicoils-threaded-insets-and-embedded-nuts-in-3d-prints-strength-amp-strength-assessment" }, { "topic": "Printed thread pull-out", "fact": "Reader-reported test of 1/4-20 printed threads in PLA+: 48 lbf (10 % infill), 68 lbf (25 %), 90 lbf (50 %), above 110 lbf (100 %, instrument limit). Failure is usually in the surrounding material (cracking, delamination) rather than the thread.", "value": "48-110+ lbf", "source_url": "https://hackaday.com/2023/11/10/putting-3d-printed-screw-threads-to-the-test" }, { "topic": "Printed draw latch anecdote", "fact": "A MakerWorld printed draw latch (26x60x15 mm, working gap 3.2-6.4 mm) survived a 5-gallon jar (about 42 lb) without breaking, though it stretched out of position; designer says thick walls matter more than infill. M3 toggle latch claims more than 10 kg lift. Informal.", "value": "about 187 N (42 lb); more than 98 N (10 kg)", "source_url": "https://makerworld.com/en/models/2266330-draw-latch" }, { "topic": "ASA tensile strength", "fact": "Bambu ASA: tensile strength 37 +/- 3 MPa (X-Y) and 31 +/- 4 MPa (Z); bending strength 65 MPa; bending modulus about 1920 MPa. Stratasys FDM ASA: tensile about 30-33 MPa, Z-strength ratio 87-91 %, Tg (DMA) 108 C, HDT 98 C @66 psi and 91 C @264 psi.", "value": "X-Y 37 MPa, Z 31 MPa; Tg 108 C", "source_url": "https://polyalkemi.no/wp-content/uploads/2024/01/Bambu_ASA_Technical_Data_Sheet.pdf" }, { "topic": "ASA/PETG layer adhesion", "fact": "CNC Kitchen hook test (Prusament): flat (in-plane) failure PLA 73 kg, PETG 55 kg, ASA 57 kg; vertical (across layers) PLA 40 kg (55 %), PETG 25 kg (46 %), ASA 17 kg (29 %); ASA vertical rises to 20 kg with a 30 C enclosure. Impact: ASA 18 kJ/m2, PETG 8.6.", "value": "ASA across-layer strength only 29 % of in-plane; PETG 46 %", "source_url": "https://cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament" }, { "topic": "Heat resistance of PETG vs ASA", "fact": "Prusament PETG HDT is 68 C at 0.45 and 1.8 MPa, tensile yield 46 +/- 1 MPa. CNC Kitchen heat test: PETG softens at 80 C and fails at about 85 C; ASA softens at 110 C and fails at 120 C; PLA fails at about 65 C. A 60-70 C enclosure surface in sun is therefore right at PETG's HDT.", "value": "PETG HDT 68 C; ASA softens 110 C", "source_url": "https://cdn.shopify.com/s/files/1/1745/6181/files/PETG_TechSheet_ENG.pdf" }, { "topic": "Creep rule of thumb (low reliability)", "fact": "A vendor blog (QIDI) says PETG shows noticeable creep at room temperature above about 30 % of yield and recommends a safety factor of 4-5 for brackets; no study cited. A 2024 paper notes most FDM datasheets omit creep data; one thesis found 80 % infill PETG creep modulus 1150-1300 MPa vs 690-710 MPa at 20 % infill. No sourced creep data at 60 C was found.", "value": "about 30 % of yield sustained (unverified)", "source_url": "https://qidi3d.com/blogs/print-lab/petg-strength-wall-mounted-brackets" }, { "topic": "Printed sustained design stress", "fact": "[own estimate] Sustained design stress for printed ASA at 60-70 C with SF about 2 and stress concentrations is about 5-8 MPa in-plane and about 2 MPa across layers. With this, a single printed latch in the 70x35x30 mm envelope is expected to hold about 100-400 N sustained (peak about 2-4x) in ASA; PETG is lower at 60-70 C. PA-CF/PETG-CF might raise this but no sourced mechanical data was gathered.", "value": "about 100-400 N sustained (ASA)", "source_url": "https://polyalkemi.no/wp-content/uploads/2024/01/Bambu_ASA_Technical_Data_Sheet.pdf" }, { "topic": "CF-filled filament heat resistance (retailer-sourced)", "fact": "Retailer comparison tables list HDT (0.45 MPa) PA6-CF about 186 C, PAHT-CF about 194 C, PET-CF about 205 C versus about 69 C for PETG; not verified in the Bambu TDS PDFs (not parseable). PA6-CF is moisture sensitive.", "value": "HDT 186-205 C (CF grades) vs 69 C (PETG)", "source_url": "https://www.3djake.com/bambu-lab/pa-pet" }, { "topic": "Outdoor material choice", "fact": "Filament guides rank ASA as the first choice when UV and weather resistance matter; PETG is less UV resistant (claims conflict); none give years-of-exposure test data.", "value": "ASA preferred for sun", "source_url": "https://www.3djake.com/info/guide/outdoor-ready-filaments-for-weather-resistant-3d-prints" }, { "topic": "TPU 85A stiffness", "fact": "NinjaFlex-type 85A TPU: Shore 85A, tensile modulus 12 MPa (ASTM D638), tensile strength 26 MPa, elongation 660 %. Gent's relation gives about 13.2 MPa for Shore 85A [own calculation using the Wikipedia formula], consistent with the datasheet.", "value": "E about 12-13 MPa", "source_url": "https://plahunter.pages.dev/data-sheets/ninjatek/tpu-ninjaflex" }, { "topic": "TPU 85A compression set", "fact": "BASF Ultrafuse TPU 85A: compression set 26 % at 23 C/72 h and 52 % at 70 C/24 h (ISO 815). ColorRx TPU 85A (ASTM D395B): 16 % at 23 C/22 h and 40 % at 70 C/22 h. Stratasys FDM TPU 92A: 44 % at 70 C/22 h.", "value": "26-52 % set at 70 C", "source_url": "https://www.dream3d.co.uk/wp-content/uploads/2022/12/Ultrafuse_TPU_85A_TDS_EN_v2.5.pdf" }, { "topic": "Preload loss from compression set", "fact": "[own calculation] With a rigid (displacement-controlled) latch and a gasket compressed 20 %, a 52 % set leaves about 10 % compression and roughly 58 % less force; a 26 % set leaves about 15 % and about 30 % less force (neo-Hookean estimate). Spring-loaded or re-tensionable latches keep the force.", "value": "about 30-58 % preload loss", "source_url": "https://www.dream3d.co.uk/wp-content/uploads/2022/12/Ultrafuse_TPU_85A_TDS_EN_v2.5.pdf" }, { "topic": "Solid TPU 85A line load", "fact": "[own calculation, +/- 2x] Neo-Hookean with E=12 MPa gives 1.3, 2.1, 3.1 and 4.1 MPa at 10, 15, 20 and 25 % compression (frictionless); bonded/constrained strip with shape factor 0.5 multiplies by about 1.5. So the line load per mm of bead width is about 2-6 N/mm at 15-25 % compression: about 4-12 N/mm for a 2 mm wide solid bead. Printed fill pattern changes TPU 85A compression force by about 2x (circular infill highest).", "value": "about 4-12 N/mm for a 2 mm bead", "source_url": "https://reference-global.com/article/10.2478/aucts-2024-0004" }, { "topic": "Foam / low-force gasket reference", "fact": "Rogers: foam gaskets are compressed 25-35 %; compression force deflection (CFD) classes at 25 %: below 10 psi (easy closure, plastic housings), 10-30 psi, above 30 psi (heavy-duty). Low-closure-force EMI gaskets are quoted about 1-8 lbf/in (about 0.18-1.4 N/mm). Solid TPU 85A is therefore roughly 5-60x stiffer per length.", "value": "foam/EMI about 0.2-1.4 N/mm vs TPU 85A about 4-12 N/mm", "source_url": "https://rogerscorp.com/blog/2025/the-mechanics-of-enclosure-seal-design-gap-spacing-cfd-and-compressibility" }, { "topic": "Minimum compression for a seal", "fact": "A nuclear-packaging analysis cites prototypic seal testing demonstrating a pressure seal needs a minimum of 10-12 % compression; Rogers warns under-compression leaks and over-compression can bottom out or warp thin enclosures.", "value": "min 10-12 % compression", "source_url": "https://www.nrc.gov/docs/ML1419/ML14195A258.pdf" }, { "topic": "Printed TPU gasket geometry examples", "fact": "A MakerWorld printed enclosure uses a TPU gasket 2.2 mm wide x 1.2 mm tall at about 25 % designed compression (test-fitted, not force-measured). A Printables screw container found 95A TPU a sweet spot for stiffness and sealing force. A TPU guide suggests 2-4 mm gasket walls, 85-90A for uneven surfaces, and service below about 60-80 C.", "value": "2.2 x 1.2 mm bead at 25 %", "source_url": "https://makerworld.com/en/models/3421467" }, { "topic": "Number of latches example", "fact": "[own calculation] A 150x100 mm lid (perimeter 500 mm) with a 2 mm solid 85A bead at 20 % compression needs about 6-9 N/mm, i.e. 3-4.5 kN total, or 12-18 printed latches at 250 N each. A thin lip or hollow profile at 1-2 N/mm needs about 0.5-1 kN, i.e. 2-4 latches.", "value": "12-18 latches vs 2-4 latches", "source_url": "https://rogerscorp.com/blog/2025/the-mechanics-of-enclosure-seal-design-gap-spacing-cfd-and-compressibility" }, { "topic": "Latch spacing rule of thumb (published)", "fact": "Only one published rule was found: flanged screw-conveyor covers are bolted on 12-inch (about 305 mm) centres with a compressible gasket (dust-tight, metal cover). Engineers Edge says spacing depends on plate thickness, allowable gasket pressure and flange dimensions (formula behind a paywall). Rogers recommends FEA or pressure-sensitive film to find low-compression zones. Southco/EMKA publish no latch-spacing rule.", "value": "12 in (305 mm) centres, dust-tight metal covers", "source_url": "https://www.kwsmfg.com/wp-content/themes/va/pdf/AtE-seals-screw-conveyor-covers.pdf" }, { "topic": "Latch spacing vs rim stiffness", "fact": "[own calculation] Simply-supported rim strip, E=2000 MPa, allowing 0.3 mm bow between latches: a flat 3x15 mm flange gives max spacing 24-35 mm for gasket line loads of 5-1 N/mm; a 3 mm wall 12 mm deep gives 45-67 mm; a 3 mm wall 25 mm deep gives 78-116 mm. A continuous rim over many latches allows about 1.5x more. Lid stiffness, not the latch, usually sets spacing for solid TPU.", "value": "24-116 mm depending on rim depth", "source_url": "https://engineersedge.com/general_engineering/gasket_cover_compression.htm" }, { "topic": "Threaded cap axial force", "fact": "[own calculation] 50 mm printed screw cap, 4 mm lead, mean diameter 48 mm: 2 / 3 / 4 Nm hand torque gives about 250-370 / 380-550 / 510-730 N axial (mu 0.3-0.2). On a 157 mm circumference this is only about 1.6-4.6 N/mm line load.", "value": "250-730 N", "source_url": "https://hackaday.io/project/12125/log/41900" }, { "topic": "Bayonet ramp force", "fact": "[own calculation] F=T/(r*tan(alpha+phi)): at 2 Nm, 25 mm radius, ramp 3 / 5 / 10 degrees and friction 0.2 gives about 314 / 273 / 205 N; at friction 0.3 about 223 / 201 / 159 N.", "value": "about 160-310 N", "source_url": "https://makerworld.com/models/1924555" }, { "topic": "V-band mechanics", "fact": "Huddersfield studies: axial clamp load of V-section band clamps increases with band pretension and with friction; ultimate-load models tended to over-predict test results; NASA Marman clamp guideline GD-ED-2214 is the standard design reference.", "value": "qualitative only", "source_url": "https://eprints.hud.ac.uk/id/eprint/22987/1/eng-2015-0010.pdf" }, { "topic": "Magnetic catch ratings", "fact": "K&J 2x1/2 in magnetic latch is rated 20 lb pull (about 89 N) against a thick steel plate at contact; a typical cabinet catch is 30 N. Ratings are at contact; a gasket gap reduces force.", "value": "30-89 N", "source_url": "https://www.kjmagnetics.com/ml-l-y0-magnetic-latches-for-cabinets-doors-drawers" }, { "topic": "Double-throw case latch rating", "fact": "Penn Elcom medium recessed butterfly latch: maximum working load 90 kg (about 880 N), 1.2 mm zinc-finished steel.", "value": "90 kg (about 880 N)", "source_url": "https://translations.penn-elcom.com/medium-mol-recessed-latch-with-padlock-bracket-in-deep-dish-l905-928pbz" }, { "topic": "Pelican press-and-pull materials", "fact": "Pelican Storm cases: latch material Valox (PBT) with Xenoy alternate; seal is an EPDM O-ring. No force values published.", "value": "PBT latch + EPDM O-ring", "source_url": "https://www.pelican.com/us/en/product/cases/iM2435/pdf" }, { "topic": "Printed cam-latch box seal test", "fact": "zx82net printed rugged box: cam latch applies significant static pressure to the TPU seal vs a clip latch; a thick TPU seal with tight latches kept water out at 10 cm for 10 min while a thin seal let in about 10 ml. Unit remains water-resistant not certified IP.", "value": "10 min at 10 cm submersion", "source_url": "https://www.thingiverse.com/thing:3338826" }, { "topic": "Printed enclosure water tests", "fact": "A Hackaday.io printed enclosure with 6 mm silicone tubing and a 2.5 mm rounded lid ridge stayed dry for 2 hours submerged, but a different variant leaked at 24 hours; author says ridge geometry mattered more than sealant and design is water-resistant not waterproof.", "value": "2 h submersion", "source_url": "https://hackaday.io/project/174011-water-resistant-3d-printed-enclosures" }, { "topic": "Multi-point latching", "fact": "For large door spans a multi-point latch is recommended (no spacing or force numbers given); single-point compression latches pull about 6 mm against the gasket.", "value": "qualitative", "source_url": "https://www.magazine-industry-usa.com/news/1936-getting-the-latch-and-hinge-specification-right" }, { "topic": "Search coverage limits", "fact": "The shared WebSearch budget was exhausted mid-task; Southco, Penn Elcom (main site), Essentra, Printables, MakerWorld and Thingiverse pages returned HTTP 403, so several figures are from search-result text or distributor copies. No data found for Protex, Pinet, Fastenal, bail/wire latches, wedge latches or PC mechanical properties.", "value": "gaps listed", "source_url": "https://southco.com/en_gb_int/E8" } ] }, { "key": "maker", "summary": "Scout result: 20 mechanism families, each with concrete example designs. Almost no designer or commenter has published a measured clamp or pull-off force for a printed box latch. The only designer figure is \"holds at least 10 kg in PLA\" on one MakerWorld latch (which model is uncertain). The other quantitative evidence is indirect: material coupon tests (CNC Kitchen, Tom's 3D, Bambu datasheets), insert and thread pull-out tests, and commercial steel latch ratings. So every sustained and peak force figure marked OWN ESTIMATE below is my own order-of-magnitude judgement, not a measurement, and must be validated by a pull test.\n\nBasis of the own estimates (assumptions):\n- Load path in the layer plane, ASA, 4+ perimeters, 100% infill in the stressed section.\n- Short-term in-plane strength about 37 MPa (Bambu ASA TDS, XY).\n- Across-layer hook strength about 0.29 of in-plane (CNC Kitchen ASA hooks: 17 kg vertical vs 57 kg flat).\n- Sustained allowable stress at 60-70 C taken as 15-25% of short-term strength. This is judgement covering creep, porosity and SF 2, giving roughly 5-9 MPa in-plane.\n- Sustained bearing stress about 8-10 MPa under steel pins or washers.\n- PETG is at or above its glass transition (about 68-80 C) in 60-70 C sun, so treat PETG sustained values as at most half the ASA values. PC, PA6-CF and PETG-CF change the answer mainly through heat margin and stiffness: PETG-CF HDT is only 68 C, PA6-CF HDT is 164 C but it is hygroscopic.\n\nIndicative ordering by realistic sustained clamp force per latch inside the 70x35x30 mm envelope (own judgement):\n1. Steel over-center draw or toggle latch on printed bosses. Commercial ratings are 135-670 N, with the printed mount as the limit (about 300-600 N, own estimate).\n2. Screw-down lid with heat-set inserts and a metal sleeve or washer. About 300-500 N per screw, own estimate. It is not a quick latch.\n3. Steel-pin-reinforced printed toggle latch, about 120-250 N.\n4. Printed cam latch with M3 pivots, about 60-150 N.\n5. Assembled printed over-center draw latch, about 40-100 N.\n6. Print-in-place over-center, bayonet, quarter-turn and snap-fit catches, about 10-60 N each.\nThe ranking is estimated, not measured.\n\nOutdoor material guidance from sources:\n- ASA beats PETG for sun-exposed latches. Vendor and forum reports put PETG yellowing and embrittlement at 6-12 months.\n- PETG creeps under sustained load above about 40 C in vendor guidance.\n- Never load a printed ASA or PETG hook across layer lines.\n\nSealing and test status:\n- Every printed IP67 or waterproof claim found is a designer assertion. At best it is a 10 cm, 10 minute dunk. Several designs explicitly say they are not IP-certified.\n- Designs that explicitly pair a latch with a TPU gasket: the MakerWorld Tough Case (TPU 85A gasket, PETG snap-fit latches, steel-pin hinges), the zx82net cam-latch box (printed TPU seal or a 2 mm cord), MakerWorld Waterproof Box 454290, and the MakerWorld print-in-place latch box 2435156.\n\nSource limits:\n- Printables, MakerWorld, Thingiverse, MyMiniFactory, stlfinder and 3dgo pages returned HTTP 403 to WebFetch, so descriptions of those listings come from search-result summaries and the few mirrors that loaded. A listing ID that I could not map exactly is flagged in the entry.\n- The 200-search budget ran out before I could run the last three searches: an IP67 test blog, wire-bail jar-style latches, and thumbscrew or wing-nut lid clamps.", "key_facts": [ { "topic": "Test evidence gap", "fact": "No designer, commenter, video or paper found that reports a measured sustained clamp force or pull-off force for a printed box latch. The only designer figure is a MakerWorld latch claimed to hold at least 10 kg (about 98 N, own conversion) in PLA Basic using stacked dumbbell plates, with the note that PETG might be more robust. Which MakerWorld model it is could not be pinned down (candidates 2036484, 2713704, 891931).", "value": "10 kg (about 98 N) static hang, PLA, designer claim", "source_url": "https://makerworld.com/models/2036484" }, { "topic": "Layer adhesion vs in-plane strength (hooks)", "fact": "CNC Kitchen hook test on a stock Prusa MK3S: printed flat PLA 73 kg, ASA 57 kg, PETG 55 kg. Printed vertically, so the load crosses layers: PLA 40 kg (55%), PETG 25 kg (46%), ASA only 17 kg (29%). PETG stretched instead of snapping.", "value": "ASA 57 kg flat vs 17 kg across layers", "source_url": "https://cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament" }, { "topic": "Warm chamber helps ASA layer bonding", "fact": "ASA printed in a roughly 30 C enclosure reached 20 kg across layers vs 17 kg, about 20% better.", "value": "17 kg to 20 kg (+20%)", "source_url": "https://cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament" }, { "topic": "Softening under load vs temperature", "fact": "In CNC Kitchen's oven test of loaded parts, PLA started sagging at 60 C, PETG at 80 C and ASA at about 110 C, failing roughly 5-10 C later. This is a short-term softening test, not creep data.", "value": "PLA 60 C, PETG 80 C, ASA 110 C onset", "source_url": "https://cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament" }, { "topic": "PETG pull test, orientation", "fact": "Tom's 3D ring pull test: PETG held 24.5 kg printed standing (layer adhesion) and about 70.8 kg printed flat (author's doubled equivalent from half-thickness rings); PLA held 16.5 kg standing and about 20.75 kg flat. Single specimens, custom test.", "value": "PETG 24.5 kg standing / about 70.8 kg flat", "source_url": "https://toms3d.org/2020/03/02/elegoo-resin-vs-prusa-resin-vs-petg-vs-pla/" }, { "topic": "Bambu PETG-CF datasheet", "fact": "Tensile strength 59 +/- 4 MPa (XY) and 38 +/- 3 MPa (Z); modulus 2460 / 1340 MPa; HDT 68 C at 1.8 MPa and 74 C at 0.45 MPa; Vicat 85 C; Tg 68 C. Specimens were 100% infill, annealed and dried at 65 C for 8 h, so as-printed parts will be weaker. The sheet's 'Basic Info' text wrongly calls it a tough PLA, a template slip.", "value": "XY 59 MPa, Z 38 MPa, HDT 68 C", "source_url": "https://cdn.shopify.com/s/files/1/0380/5149/files/Bambu_PETG-CF_Technical_Data_Sheet.pdf" }, { "topic": "Bambu PA6-CF datasheet", "fact": "Tensile strength 102 +/- 7 MPa in XY; modulus 4430 MPa XY vs 2170 MPa Z; HDT 164 C at 1.8 MPa and 186 C at 0.45 MPa. Strength and stiffness drop when the nylon absorbs water, so condition it for outdoor use. Figures are from search-result snippets of the PDF; the direct fetch returned 404.", "value": "XY 102 MPa, HDT 164 C", "source_url": "https://polyalkemi.no/wp-content/uploads/2024/01/Bambu_PA6-CF_Technical_Data_Sheet-v2.pdf" }, { "topic": "Bambu ASA datasheet", "fact": "The V3.0 sheet lists tensile strength 37 +/- 3 MPa (XY) and 31 +/- 4 MPa (Z); the older V2.0 listed Z as 35 +/- 4 MPa. V2.0 elongation at break was 9.2% XY vs 4.6% Z. From search-result snippets only; the direct fetch returned 404.", "value": "XY 37 MPa, Z 31 MPa", "source_url": "https://polyalkemi.no/wp-content/uploads/2024/01/Bambu_ASA_Technical_Data_Sheet.pdf" }, { "topic": "Material temperature ratings", "fact": "Prusament PETG is listed at 68 C and Prusament ASA at 93 C temperature resistance. The page stresses these are not universal operating limits or maximum ambient temperatures.", "value": "PETG 68 C, ASA 93 C", "source_url": "https://www.goodprints3d.com/blogs/3d/best-filament-for-outdoor-junction-boxes-and-sensor-enclosures-petg-or-asa" }, { "topic": "QIDI heat data and creep bands", "fact": "QIDI datasheet values: HDT PLA 57.6 C, PETG 71.8 C, PETG-GF 76 C; Vicat 61.6 / 79.7 / 85 C. Vendor guidance for a hook under 3 kg: PLA droops within weeks at 30-40 C, PETG sags slowly over months at 30-40 C and creeps noticeably above 40 C. Recommends 4-6 walls, PETG-GF above 10 kg load, ASA outdoors, safety factor 3x (5x overhead) and replacing heavily loaded parts after about two years. Qualitative vendor blog, no deformation numbers.", "value": "PETG HDT 71.8 C; noticeable creep above 40 C", "source_url": "https://qidi3d.com/blogs/print-lab/pla-petg-heavy-wall-hook-material-guide" }, { "topic": "No universal sustained-stress fraction", "fact": "The filamentspecs creep review states there is no universal safe percentage of tensile strength for creep, and that Tg, HDT and Vicat are not continuous-use limits. It cites: PETG honeycomb infill has about 15% lower long-term creep strain than line infill despite 14% lower tensile strength; an accelerated stepped-isostress PETG method takes 25 h vs 720 h; bolted PLA/PETG joints lost about 3% (PLA) and 11.5% (PETG) clamping force in seven days. Recommends avoiding sustained tension across layer interfaces, metal compression limiters under bolts, conditioning nylon, and defining allowable displacement before testing.", "value": "PETG bolt preload loss 11.5% in 7 days vs PLA 3%", "source_url": "https://filamentspecs.com/creep-resistance-3d-printed-parts/" }, { "topic": "PETG creep modeling paper", "fact": "A 2025 paper on accelerated creep prediction in printed PETG (stepped iso-stress method) reports about 15% lower long-term creep strain for honeycomb vs line infill at 10^6 s despite 14% lower tensile strength. Only the abstract was visible.", "value": "-15% creep strain, honeycomb vs line", "source_url": "https://www.sciencedirect.com/science/article/abs/pii/S1350630725008611" }, { "topic": "Heat-set insert pull-out in PETG", "fact": "CNC Kitchen, PETG M3 samples, 4 perimeters and 100% infill: pull-out averaged 119 kg for a Ruthex heat-set insert (it ripped out), 118 kg for a screw straight into plastic, 120 kg for a helicoil, 86 kg for a nut in a side pocket and 166 kg for a nut in a bottom pocket. Torque-out: insert 3 Nm vs 1 Nm direct screw. 119 kg is about 1.17 kN (own conversion).", "value": "119 kg (about 1.17 kN) M3 insert in PETG", "source_url": "https://www.cnckitchen.com/blog/helicoils-threaded-insets-and-embedded-nuts-in-3d-prints-strength-amp-strength-assessment" }, { "topic": "Heat-set insert pull-out in PLA", "fact": "CNC Kitchen, Prusament PLA, 0.15 mm layers, 100% infill: M3 pull-out 181 kg for Ruthex, 157 kg for an eBay insert, 39 kg for a cheap injection-moulding insert, 142 kg for a screw straight into the plastic. Insert pull-out is well above any printed latch load, so the printed boss, not the insert, is the limit.", "value": "181 kg (about 1.78 kN, own conversion) Ruthex M3 in PLA", "source_url": "https://www.cnckitchen.com/blog/threaded-inserts-for-3d-prints-cheap-vs-expensive" }, { "topic": "Insert white paper figures (low confidence)", "fact": "A threaded-insert white paper reports average pull strengths of about 1,304 N (M3), 2,704 N (M4) and 3,421 N (M5), but the table's material labels are unclear, so treat these as approximate. The direct fetch returned 404; figures are from a search snippet.", "value": "M3 1,304 N / M4 2,704 N / M5 3,421 N", "source_url": "https://felix-manley-n4jm.squarespace.com/s/Threaded-Inserts-White-Paper-V1.pdf" }, { "topic": "Threaded parts failure mode", "fact": "In a Hackaday-reported M5 comparison of 50 parts, threads rarely failed. The surrounding material cracked or delaminated, and thicker shells around holes improved strength. Brass inserts were hard to pull out or twist. No force figures given.", "value": "Failure is in the surrounding wall, not the thread", "source_url": "https://hackaday.com/2019/03/26/threaded-3d-printed-part-comparison" }, { "topic": "Clamping splits layers", "fact": "In a printed waterproof instrument housing log (PLA, bolts and washers), parts printed off the bed were too weak: the layers split under the clamping force. An epoxy-coated cap allowed much tighter bolting, but an uncoated collar then began to split.", "value": "Layer splitting under bolt clamping", "source_url": "https://hackaday.io/project/12125/log/41900" }, { "topic": "Latch stiffness matters", "fact": "In MatterHackers' printed-carabiner tests the author found that the more flexible the filament, the more easily the latch unseats; polycarbonate scored highest, and nylon's lower stiffness hurt its result. PETG was stronger than PLA but failed violently. Hardware-store aluminium carabiners rated 150 lb failed at 168 and 183 lb with latches taped open.", "value": "Stiffer material keeps the latch seated", "source_url": "https://www.matterhackers.com/news/filament-strength-testing" }, { "topic": "Layer-separation failure of printed PETG latches", "fact": "A Cybertruck owner forum reports PETG release handles failing by layer separation, consistent with the rule never to load a printed latch across layer lines.", "value": "PETG latch delamination anecdote", "source_url": "https://www.cybertruckownersclub.com/forum/threads/emergency-exit-rear-door-release-ideas.49045/post-30750355" }, { "topic": "PETG vs ASA outdoors (vendor and forum)", "fact": "A QIDI vendor blog says PETG brackets in high UV showed yellowing and surface embrittlement in 6-12 months while ASA held colour and strength for about 2-3 years. A forum poster reports PETG yellowing after 8-10 months of direct sun but staying rigid, and ABS showing little UV damage after about 2 years. These are anecdotes, not controlled tests.", "value": "PETG 6-12 months to embrittlement vs ASA 2-3 years (vendor)", "source_url": "https://qidi3d.com/ja/blogs/print-lab/asa-petg-sprinkler-brackets-outdoor" }, { "topic": "Forum field report on outdoor enclosures", "fact": "A circuit.rocks poster with outdoor enclosures deployed about two years saw PETG yellow after 8-10 months but stay functional; ABS units showed almost no visible UV damage; ASA recommended for 5+ year service. No latch or lid failures were reported in the thread.", "value": "PETG yellowing 8-10 months", "source_url": "https://forum.circuit.rocks/post178.html" }, { "topic": "Lid seam leaks first", "fact": "An outdoor-enclosure guide says a 3D-printed box is rarely waterproof by default and the lid seam usually fails first, so gasket design matters more than material choice. Another guide recommends a deliberate lip or labyrinth, a hard compression stop, a narrow raised bead over a wide flat band, and keeping screw holes and seams out of the sealing band.", "value": "Seam and gasket design over material", "source_url": "https://www.sovol3d.com/blogs/news/3d-printed-electronics-enclosure-for-smart-gardening-what-actually-matters-outdoors" }, { "topic": "Gasket guidance (TPU hardness)", "fact": "TPU 95A is suggested as the starting point for most low-pressure gaskets, and 85A-90A for uneven surfaces or low clamp force; Shore hardness alone does not define a gasket (compression set, tear strength and rebound vary). No compression percentage or N/mm line load is given. The search found no published compression force per length for TPU 85A, so that must be measured or calculated separately (the gasket role).", "value": "85A-90A for low clamp force", "source_url": "https://www.goodprints3d.com/blogs/3d/best-filament-for-3d-printed-gaskets-and-seals-tpu-95a-soft-tpu-or-tpe" }, { "topic": "Printed seal leak tests", "fact": "A Hackaday.io log of a printed case with 6 mm silicone tubing in a groove and a rounded 2.5 mm lid ridge: no leak at 10 min, 1 h and 2 h submerged. An earlier variant leaked at 24 h and after 1-2 h. 3M silicone sealant leaked within seconds. The author calls it water-resistant, not waterproof, because layer gaps let moisture in.", "value": "Dry at 2 h submerged, leaks by 24 h in other variants", "source_url": "https://Hackaday.io/project/174011-water-resistant-3d-printed-enclosures" }, { "topic": "zx82net box leak test", "fact": "A reviewer submerged the zx82net rugged box under 10 cm of water for 10 minutes: no leakage with the thick seal, about 10 ml in with the thin seal. The designer recommends PETG for latches and hinges and warns PLA may creep, loosening the seal.", "value": "10 cm, 10 min: dry (thick seal) / about 10 ml (thin seal)", "source_url": "https://www.myminifactory.com/object/3d-print-zx82net-customizable-rugged-waterproof-box-146437" }, { "topic": "IP claims are unverified", "fact": "No printed-enclosure listing found cites an IP test report. One MakerWorld/Thangs parametric enclosure says explicitly it is not independently tested or certified to any IP rating. A Printables box is labelled IP65/IP67 with no test. A rated vent does not make a printed box IP67 or NEMA-rated.", "value": "0 listings with IP test evidence", "source_url": "https://printables.com/model/72839-customizable-parametric-stable-and-waterproof-elec" }, { "topic": "Printed TPU O-rings vs rubber", "fact": "The Printables EDC container designer does not recommend self-printed TPU O-rings because their tests performed worse than original ones; a MakerWorld canister designer says they trust the O-ring more than the TPU seal. Under-extrusion lets water through the printed seal itself.", "value": "Rubber O-ring beat printed TPU in two designers' tests", "source_url": "https://www.printables.com/model/181253-edc-container-box-capsule-o-ring" }, { "topic": "Material and recommendations in the Tough Case", "fact": "MakerWorld Rugged Waterproof Tough Case recommends ABS for the body, TPU 85A for the gasket and PETG for clips and latches, with steel-pin hinges. It gives no force, IP or leak data. Inner dimensions 115 x 76 x 38 mm.", "value": "ABS body / TPU 85A / PETG latches", "source_url": "https://www.makerworld.com/en/models/2385298" }, { "topic": "Real-world latch lifetime", "fact": "The designer of the Pentair LXLATCH replacement says the original pool-controller latches broke after about a decade in the sun and recommends UV-resistant ABS, PETG or PC.", "value": "about 10 years to failure (original latch)", "source_url": "https://www.stlfinder.com/model/replacement-for-pentair-lxlatch-NuK4TAoL/5223236" }, { "topic": "Commercial steel latch clamp ratings", "fact": "Southco 97-series over-center draw latches: 97-30 compact 135 N; light-duty 310 N; heavy-duty 670 N; a 290 N size; 97-70 645 N. Bossard BN 32753: 260-530 N. These set the benchmark a printed latch has to approach.", "value": "135-670 N", "source_url": "https://www.gripwell.com.sg/image/catalog/Gripwell/Furniture and Architectural Hardware/Latches/Draw Latches/97 Over-Center Draw Latch/Gripwell - 97 Over-Center Draw Latch.pdf" }, { "topic": "Pelican reference", "fact": "Pelican's Storm-series cases use a PBT (Valox) latch and an EPDM O-ring seal; Pelican publishes no latch clamp-force number, so no direct benchmark exists.", "value": "PBT latch + EPDM O-ring, no force published", "source_url": "https://www.pelican.com/ca/en/product/cases/im2306" }, { "topic": "Pin hardware for printed pivots", "fact": "Makers use steel pins: 3 mm steel and stainless pins in the MakerWorld toggle latch, a 2 mm bicycle spoke in engineered.at's box, 1.6 mm spring wire in a Printables panel latch, and a stainless pin added to a PETG caravan latch for shear. Pin sizes only; no tested load gains are published.", "value": "1.6-3 mm steel pins", "source_url": "https://makerworld.com/en/models/1054989-self-locking-toggle-latch" }, { "topic": "Snap-fit design rules", "fact": "Guides suggest about 3% allowable strain for PETG and ABS/ASA snap arms printed flat and about half that printed upright; a Z-oriented cantilever loses about 50% elongation at break and 20-30% tensile strength. These are design heuristics, not measurements.", "value": "3% strain flat, 1.5% upright", "source_url": "https://buildcad.ai/snap-fit-3d-printing" }, { "topic": "Orientation advice from makers", "fact": "Makers advise 100% infill on the moving latch part (small locking arms break first), 3 perimeters and over 30% infill on cam-latch boxes, and printing the latch in the plane of the arm. The cam-latch box listing was tested only in PLA and PETG.", "value": "100% infill on cam arm", "source_url": "https://www.printables.com/model/355435-cam-latch-for-boxes" }, { "topic": "Blue Robotics printed clips", "fact": "Blue Robotics staff say the BlueROV2 was prototyped with 3D-printed clips about twice the size of the aluminium ones, and they worked fine.", "value": "2x scale vs aluminium", "source_url": "https://discuss.bluerobotics.com/t/enclosure-clips/2854" }, { "topic": "Search coverage limits", "fact": "Printables, MakerWorld, Thingiverse, MyMiniFactory, stlfinder, 3dgo and PMC returned HTTP 403 or verification pages to WebFetch, and the 200-search budget ran out before three planned searches (IP67 test blog, wire-bail jar-style latches, thumbscrew or wing-nut lid clamps). Listing details are from search summaries, so verify any listing before relying on it.", "value": "403 on most maker sites; 200/200 searches used", "source_url": "https://makerworld.com/en/models/454290-waterproof-box" } ] }, { "key": "testdata", "summary": "Research on measured force and creep data for FDM latch parts. It found plenty on fastener interfaces and hook orientation, but almost nothing measured on whole latches.\n\n**What exists**\n- Peak strength: CNC Kitchen hook tests, heat-set insert and screw tests, datasheets, and one printed draw latch that held at least 187 N without failing.\n- No measured force for a printed cam lever, bayonet or toggle latch beyond that one draw-latch lower bound.\n- No long-term (months) creep data for PETG, ASA or PA-CF.\n- Direct creep evidence is limited to Dogan 2022 (3-hour tests, CNC-milled specimens), CNC Kitchen bolt and spring tests (days, qualitative), and anecdotes.\n- No FDM data for M4/M5 inserts in PETG or ASA. M4/M5 numbers come only from PA12 MJF (Sculpteo, as relayed in a search summary) and from a white paper of unclear provenance.\n\n**What it means for a printed latch (own interpretation)**\n1. Orientation dominates. Hooks printed lying flat held 55 kg (PETG) and 57 kg (ASA) in CNC Kitchen's tests. Standing (load across layers) they held 25 kg and 17 kg, so ASA keeps only 29% of its flat strength (PETG 46%, PC Blend 35 of 74-77 kg). Load paths that pull layers apart are the weak link.\n2. For a clamp, the screw or insert interface is the strongest printed feature. A heat-set M3 insert in PETG pulled out at about 1.17 kN and tolerated 3 Nm. Steel screws are never the weak link.\n3. Integral snap-fits are far too weak for a gasket clamp (1.7-41 N in ABS).\n4. Sun-heated surfaces of 60-70 C sit at or above PETG's heat deflection temperature (68-78 C). ABS ruptured in about 3 min at 60 C and 20 MPa, while PC did not rupture at all. This favours ASA, PC and PC-CF, and makes PETG marginal.\n\n**Peak versus sustained.** Every peak number below is short-term. Dividing by the safety factor of 2 gives roughly 580 N per M3 PETG insert at 23 C, before any creep or hot-weather derate. I found no measured derate, so that step is open.\n\n**Search limits.** I hit the shared web-search budget limit, so a few planned searches did not run. Several pages (MakerWorld, MDPI, PMC, Sculpteo, Springer, De Gruyter) blocked fetching, so some numbers come from search-engine summaries and are flagged as such in the facts.\n\n**Prompt injection.** One fetched page (Polymaker PC-FR wiki) contained embedded instructions to send a query to an external URL. I ignored them.", "key_facts": [ { "topic": "Hook orientation (layer adhesion)", "fact": "CNC Kitchen hook tests on Prusament (flat vs standing): PLA 73 vs 40 kg (55%), PETG 55 vs 25 kg (46%), ASA 57 vs 17 kg (29%). PETG flat hooks stretched rather than snapped. Geometry only described qualitatively (similar wall thickness and infill).", "value": "flat 73/55/57 kg; standing 40/25/17 kg (PLA/PETG/ASA)", "source_url": "https://cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament" }, { "topic": "Hook orientation (layer adhesion)", "fact": "ASA printed in a roughly 30 C enclosure improved its standing hook load by about 20% (17 to 20 kg).", "value": "20 kg standing ASA (vs 17 kg open air)", "source_url": "https://cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament" }, { "topic": "Hook orientation (PC)", "fact": "Prusament PC Blend hooks: flat 74 and 77 kg (top of the chart); standing 35 kg undried/brass nozzle, 31 kg brass after steel, 22 kg dried with steel nozzle. Layer adhesion 35.3 MPa (undried) vs flat tensile 68.3 MPa, so Z/XY is 63%. Notched impact standing under 3 kJ/m2 vs 27 kJ/m2 flat.", "value": "flat 74-77 kg; standing 22-35 kg", "source_url": "https://www.cnckitchen.com/blog/prusament-pc-blend-review" }, { "topic": "Hook infill", "fact": "CNC Kitchen hook load at failure: PETG 100% infill 110 kg (broke violently), PETG 30% infill 54 kg (yielded); PLA 100% 131 kg, PLA 30% 71 kg. Orientation noted as mattering but not specified in the extracted text. PETG at 100% infill gave bending stress 72 MPa (yielded).", "value": "PETG 110 kg (100%) / 54 kg (30%)", "source_url": "https://www.cnckitchen.com/blog/whats-stronger-3d-prints-or-wood" }, { "topic": "Hook, standing box (Searchwing)", "fact": "Searchwing standing-box hook tests (0.2 mm layer, random seams, 30% infill, suitcase scale), single hook / double part break loads: PETG Amazon Basic 0.5/9 kg, PETG Extrudr 4/35 kg, PETG 3DJake 4/30 kg; ABS no-name 2/18, TitanX 3/20, 3DJake 4/30; ASA Extrudr DuraPro 6.5/29 (with shield), 6/25 (without), 6/35 (acetone-vapour treated); ASA 0.6 mm nozzle 100% infill 12/50+. PLA Prusa 7-8/29. Crude method but it shows the large brand-to-brand spread.", "value": "single hook 0.5-12 kg depending on material/brand", "source_url": "https://hackmd.io/@searchwing/TestPrintsStrenght" }, { "topic": "Layer adhesion vs print angle (PLA)", "fact": "PLA tensile strength by print angle (CNC Kitchen, Prusa CORE One, 0.2 mm): flat 63 MPa, 30 degrees 44, 45 degrees 40, 60 degrees 36, upright 31. 45 degrees gives about 27-29% more than upright. Layer adhesion is typically about 50% of in-plane strength depending on material and settings. Trend probably transfers to PETG/ASA but was only measured for PLA.", "value": "63 / 44 / 40 / 36 / 31 MPa", "source_url": "https://www.cnckitchen.com/blog/stop-printing-flat-the-45-secret-for-stronger-parts" }, { "topic": "Layer adhesion vs extrusion temperature (PETG)", "fact": "Standing PETG mini-tensile specimens (dasFilament): layer adhesion 18 MPa at 200 C, 22 at 215, 30 at 230, 32 at 245 (peak, about 58% of the 55 MPa lying strength), 24 at 260. Hotter or colder than the optimum costs strength. PLA peaked at 40 MPa at 230 C (lying 60).", "value": "PETG Z strength 18-32 MPa vs 55 MPa lying", "source_url": "https://www.cnckitchen.com/blog/the-influence-of-extrusion-temperature-on-layer-adhesion" }, { "topic": "Layer height and standing hooks", "fact": "Standing PLA hooks (CNC Kitchen): 0.05-0.2 mm layers all good with 0.15 mm best; 0.3 mm layers gave about half the best load; 0.4 mm gave basically no load. All standing results were at least 50% below lying (about 80 kg). Rule of thumb: layer height at or below half the nozzle diameter.", "value": "0.2 mm or less on a 0.4 mm nozzle", "source_url": "https://www.cnckitchen.com/blog/the-influence-of-layer-height-on-the-strength-of-fdm-3d-prints" }, { "topic": "Heated chamber effect (ABS, PC)", "fact": "eSUN ABS layer adhesion (reference flat 39 MPa): chamber open (up to 26 C) 21 MPa (about 54%), passively heated (just under 50 C) 23 MPa, actively heated to 65 C 29 MPa (about 75%). Prusament PC Blend: 65% / 72% / 77% of reference for open / passive / 65 C. No ASA, PETG or nylon data in this article.", "value": "ABS 21 / 23 / 29 MPa", "source_url": "https://www.cnckitchen.com/blog/does-a-heated-chamber-make-your-3d-prints-stronger" }, { "topic": "ABS vs PC layer adhesion and annealing", "fact": "ABS: about 35 MPa lying, standing about 50% of that. PC: about 70 MPa lying, standing about 80%. PC-core ABS about 60%. After annealing at 130 C for 112 h: ABS strength unchanged and distorted (about +20% in Z, -5 to -10% in XY), PC rose to almost 75 MPa with 0-2% change. Heat test: ABS failed at 115 C, PC held to 165 C.", "value": "PC Z/XY about 80%, ABS about 50%", "source_url": "https://www.cnckitchen.com/blog/pc-core-abs-testing-dual-material-filament-for-warp-less-annealing" }, { "topic": "Annealing PETG standing hooks", "fact": "PETG standing hooks went from 36 kg as printed to about 100 kg after plaster-supported annealing (about 2.8x; lying reference 106 kg), and standing tensile from 30 to 41 MPa (flat reference 53 MPa). The same treatment made PLA more than 30% weaker. This needs a 200 C oven cycle with a plaster mould, so it is impractical for large latch bodies; no data for ASA.", "value": "PETG standing hook 36 kg to about 100 kg", "source_url": "https://www.cnckitchen.com/blog/annealing-3d-prints-in-plaster" }, { "topic": "Stiffness (3-point bending)", "fact": "Bending modulus from CNC Kitchen tests: PLA 3300 MPa, ASA 2300, PETG 1900, Prusament PC Blend 2200. Notched Izod: PLA about 5, PETG about 8.6, ASA about 18, PC Blend about 27 kJ/m2.", "value": "ASA 2300 / PETG 1900 / PC Blend 2200 MPa", "source_url": "https://cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament" }, { "topic": "Temperature resistance under load", "fact": "CNC Kitchen oven test with a loaded nut: PLA starts to give at 60 C and fails about 5 C later; PETG starts to give at 80 C and fails about 5 C later; ASA softens at 110 C and fails at 120 C. Prusament PC Blend softens at about 110 C and fails at 125 C. This is a load-under-heating test, not a creep test.", "value": "PETG 80/85 C; ASA 110/120 C; PC Blend 110/125 C (soften/fail)", "source_url": "https://cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament" }, { "topic": "Heat-set insert pull-out (PETG M3)", "fact": "CNC Kitchen PETG M3 test (flat bar, 4 perimeters, 100% infill, n=3 pull-out): direct screw 118 kg, Ruthex heat-set insert 119 kg, Helicoil 120 kg, side-pocket nut 86 kg, bottom-pocket nut about 166 kg. Torque-out: direct screw 1 Nm, insert 3 Nm, Helicoil 1 Nm, nuts about 2 Nm. 1 Nm on M3 corresponds to more than 1500 N pretension. Layer height, nozzle and temperatures were not stated.", "value": "about 1.16-1.18 kN (screw/insert/coil); 3 Nm insert", "source_url": "https://www.cnckitchen.com/blog/helicoils-threaded-insets-and-embedded-nuts-in-3d-prints-strength-amp-strength-assessment" }, { "topic": "Heat-set insert pull-out (PLA M3)", "fact": "PLA M3 pull-out: Ruthex 4.0 mm hole 181 kg (about 1775 N), eBay insert 4.1 mm 157 kg (about 1540 N), cheap injection-moulding insert 4.5 mm 39 kg (about 383 N), direct-screwed 2.7 mm hole 142 kg (about 1393 N). Torque-out 3-4 Nm for all inserts (bolt head sheared) vs about 1 Nm for direct screw. In softer ASA the shallow-knurled eBay insert started rotating (no numbers). kg to N conversion is mine.", "value": "Ruthex M3 181 kg in PLA", "source_url": "https://www.cnckitchen.com/blog/threaded-inserts-for-3d-prints-cheap-vs-expensive" }, { "topic": "Insert hole diameter", "fact": "M3 inserts in PLA (n=3 per diameter, about 50 inserts): as-printed holes at the smallest diameter (3.6 mm) averaged about 1400 N (about 150 kg); pull-out fell slowly then dropped sharply with larger holes; 4.2 mm as-printed gave about 90% of the theoretical maximum; drilled holes of 4.1-4.2 mm showed a major strength drop. Printed holes were about 0.25 mm undersized relative to CAD; keep the packaging value 4.0 mm as nominal.", "value": "about 1400 N at 3.6 mm hole", "source_url": "https://www.cnckitchen.com/blog/are-our-heat-set-insert-datasheets-wrong" }, { "topic": "Insert size scaling (non-FDM)", "fact": "Sculpteo heat-set brass inserts in PA12 MJF (5 specimens each): M3 short 813 N, M3 long 1258 N, M4 1372 N, M5 above 1800 N. This is not FDM, so it indicates scaling only. Figures taken from a search-engine summary (page returned 403).", "value": "M3 813-1258 N, M4 1372 N, M5 above 1800 N", "source_url": "https://www.sculpteo.com/en/3d-learning-hub/design-guidelines/pull-out-resistance-of-threaded-inserts-testing-and-results/" }, { "topic": "Insert size scaling (white paper)", "fact": "A white paper on inserts M2-M5 in PA12, PLA, PETG and Onyx (author unclear, not independently verified; page returned 404 on fetch) reports averages of roughly 1304 N (M3), 2704 N (M4) and 3421 N (M5) across materials, plus an average insert torque strength of 4.76 Nm. Treat as low confidence.", "value": "M3 1.3 kN / M4 2.7 kN / M5 3.4 kN", "source_url": "https://felix-manley-n4jm.squarespace.com/s/Threaded-Inserts-White-Paper-V1.pdf" }, { "topic": "Thread repair vs inserts (SLS PA12)", "fact": "Peer-reviewed study on SLS PA12 (not FDM): printed threads failed at an average 3.41 kN, heat-set inserts 3.83 kN (about 12% higher), Helicoil inserts 4.78 kN (about 40% higher). Failure was thread/insert pull-out from the material in every case. Values from search summary; PMC page blocked on fetch.", "value": "3.41 / 3.83 / 4.78 kN", "source_url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC12787388/" }, { "topic": "Printed thread pull-out (PLA+)", "fact": "1/4-20 metal hook screw pulled out of printed PLA+ threads (0.2 mm layers), reader-reported averages: 48.4 lbf (10% infill), 67.5 lbf (25%), 89.5 lbf (50%), above 110 lbf (instrument limit) at 100% infill. Bottom layers peeled off. 100% infill outperformed 50%. Numbers are from a commenter, not the article text.", "value": "215 N / 300 N / 398 N / above 490 N", "source_url": "https://hackaday.com/2023/11/10/putting-3d-printed-screw-threads-to-the-test" }, { "topic": "Printed thread orientation (ASA)", "fact": "ASA M10 printed nuts (MEX): specimens oriented at 45 degrees gave the highest tensile strength but needed more material and time; formed threads in printed polymer nuts were described as completely unsatisfactory; a load capacity above 14.7 MPa is claimed for a nut printed without post-processing. Abstract only, no failure loads.", "value": "above 14.7 MPa (M10 ASA nut)", "source_url": "https://www.mmscience.eu/journal/issues/june-2025/articles/analysis-of-3d-printed-metric-nuts-manufactured-by-the-mex-method-from-asa-material" }, { "topic": "Creep at temperature (FDM polymers, 3 h)", "fact": "Dogan 2022 (Ultimaker 2+ filaments, ASTM D638 Type IV, CNC-milled 2 mm off the outside to remove print defects, ASTM D2990 method, 3 h each, n=3): ABS ruptured in about 3 min at 60 C and 20 MPa. At 25 C and 40 C nothing ruptured. At 60 C all materials except PC (and the non-rupturing nylon) broke after some time; PLA broke at 60 C even at 10 MPa. PC showed the lowest creep in all conditions and no damage at 60 C and 20 MPa; nylon showed the largest strain without rupture; creep ranking best to worst: PC, CPE, ABS, TPLA, PLA. Tertiary creep only in PLA and TPLA.", "value": "ABS rupture at about 3 min (60 C, 20 MPa); PC no rupture", "source_url": "https://ojs30.sv-jme.eu/index.php/sv-jme/article/download/191/118/2454" }, { "topic": "Creep test caveats", "fact": "The Dogan 2022 creep specimens were milled solid coupons, so they do not reflect layer-bond-limited behaviour in printed latch parts. Only three hours were tested. No PETG or ASA were included. Treat as a materials ranking, not a design allowable.", "value": "3 h; no PETG/ASA; milled specimens", "source_url": "https://www.sv-jme.eu/article/short-term-creep-behavior-of-different-polymers-used-in-additive-manufacturing-under-different-thermal-and-loading-conditions/" }, { "topic": "Long-term creep (ABS, ASA, PLA, PC, fibre)", "fact": "Hausler et al. 2024 (Open Engineering 14(1)) compared long-term creep of ABS, ASA, PLA and PC, plus fibre-reinforced grades, by measuring bending under sustained load and recovery (Prusa MK3S+, hardened 0.4 mm nozzle). Fibre reinforcement generally improved creep stability; the most promising were GreenTEC Pro Carbon and add:north PC Blend HT LCF. Numeric results not accessible (publisher blocked); only the abstract summary was read.", "value": "best: PC Blend HT LCF and GreenTEC Pro Carbon", "source_url": "https://www.degruyterbrill.com/document/doi/10.1515/eng-2024-0084/html" }, { "topic": "Bolt-preload creep", "fact": "CNC Kitchen M4 bolt test (0.8 Nm, compressive load about 50% of the material's tensile strength, 1 week, room temperature): unannealed PA6 needed re-tightening almost daily; unannealed PA12 once after about half a week, similar to PLA and ASA; annealed PA6 (8 h at 110 C) slightly twice, close to the other polymers; PLA+ also crept. Spring test at 25% of tensile strength over several days: unannealed PA6 crept most; regular PLA crept more than nylons in the first 3 days. No mm values given.", "value": "ASA about 1 retighten per week at 50% of tensile strength", "source_url": "https://www.cnckitchen.com/blog/carbon-fiber-nylon-in-3d-printing-pa6-vs-pa12-tested" }, { "topic": "Polyamide moisture", "fact": "PA6 absorbs about 3% water (75% RH, 35 C, 3 days): stiffness falls to about one third (deflection about 2 mm vs 0.7 mm dry), tensile strength retained 56%; PA12 takes up about 0.7% with essentially unchanged stiffness and about 15% strength loss. This makes PA6-CF a poor choice for humid outdoor sealing duty; PA12-CF is better but still a nylon that creeps.", "value": "PA6: 56% strength, 1/3 stiffness when wet", "source_url": "https://www.cnckitchen.com/blog/carbon-fiber-nylon-in-3d-printing-pa6-vs-pa12-tested" }, { "topic": "CF nylon strength and heat", "fact": "CF-PA6 tensile XY about 140 MPa (datasheet claims 170); CF-PA12 almost 120 MPa. Oven test with weight: PA12 softens at 160 C and fails at 170 C; PA6 first deforms at 195 C and fails at 205 C. Nozzle about 280 C and hardened steel required.", "value": "XY about 140 MPa (CF-PA6), about 120 MPa (CF-PA12)", "source_url": "https://www.cnckitchen.com/blog/carbon-fiber-nylon-in-3d-printing-pa6-vs-pa12-tested" }, { "topic": "Creep, ABS print orientation", "fact": "Zhang et al. 2018 (Purdue/IUPUI, J. Mater. Eng. Perform. 27(1)): in the printed ABS creep test the 90 degree orientation had the lowest k value (0.2) in the plastics creep model, read by the authors as the most creep-resistant direction. Numbers from search summary; the repository page did not load.", "value": "k = 0.2 at 90 degrees", "source_url": "https://scholarworks.indianapolis.iu.edu/items/b833511c-e37f-4ec3-86c9-14dfdab3c54f/full" }, { "topic": "Creep, anecdotes (labelled anecdotal)", "fact": "Forum users report PETG HF maintains tension better than PLA, PC even a bit better than PETG, nylon rivalling PLA in creep, higher temperature increasing creep. Another builder reports CF-nylon parts lost every bolt's pretension and warped under their own weight; the Voron community suggests PC or PC-CF instead. No measurements.", "value": "anecdotal only", "source_url": "https://forum.bambulab.com/t/pla-vs-petg-hf-deformation-under-load/212834" }, { "topic": "Creep, vendor heuristic (labelled vendor claim)", "fact": "A printer vendor's blog claims PETG shows noticeable creep at room temperature when loaded above about 30% of its yield strength for extended periods and recommends a safety factor of 4-5 for wall brackets. No test data or source is given; use only as a cautious rule of thumb.", "value": "about 30% of yield; SF 4-5 (vendor claim)", "source_url": "https://qidi3d.com/en-br/blogs/print-lab/petg-strength-wall-mounted-brackets" }, { "topic": "Creep, PLA below Tg", "fact": "Flexural creep experiments on printed PLA (Siegen) showed non-negligible creep over long periods even at temperatures well below the glass transition temperature, and physical aging shifts creep curves on a log-time scale. PLA only, not PETG or ASA.", "value": "PLA only", "source_url": "https://arxiv.org/pdf/2302.11240" }, { "topic": "Datasheet PETG", "fact": "Polymaker PolyLite PETG (page lists values consistent with TDS V5.4): tensile XY 50.8 +/- 0.9 MPa, Z 42.8 +/- 2.8 MPa; elongation XY 8.4%, Z 3.3%; E XY 2117 MPa, Z 1899 MPa; HDT 75 C at 1.8 MPa and 78 C at 0.45 MPa; Tg 81 C; Vicat 84 C. Specimens: 240 C nozzle, 100% infill, fan off. An older TDS (V5.2) reportedly lists Z 13.4 and XY 31.9 MPa, so datasheet Z values vary widely between revisions.", "value": "Z 42.8 MPa; HDT 75/78 C; Tg 81 C", "source_url": "https://wiki.polymaker.com/polymaker-products/more-about-our-products/documents/technical-data-sheets/petg-pet/polylite-tm-petg" }, { "topic": "Datasheet PC", "fact": "Polymaker PolyMax PC-FR (page states it is no longer made): tensile XY 67 +/- 4.5 MPa, Z 46 +/- 4.8 MPa; elongation XY 3.49%, Z 2.2%; HDT 107 C at 1.8 MPa and 110 C at 0.45 MPa; Tg 115 C. For plain PolyMax PC a search summary of the V5.3/V5.4 TDS gives tensile XY 53.44 MPa, Z 41.43 +/- 1.50 MPa.", "value": "PC Z 41-46 MPa; HDT 107-110 C", "source_url": "https://wiki.polymaker.com/polymaker-products/more-about-our-products/documents/technical-data-sheets/polycarbonate/polymax-tm-pc-fr" }, { "topic": "Datasheet PETG-CF", "fact": "Bambu PETG-CF TDS V2.0 (specimens annealed and dried at 65 C for 8 h, 100% infill): tensile XY 59 +/- 4 MPa, Z 38 +/- 3 MPa; E XY 2460, Z 1340 MPa; bending strength XY 83, Z 62 MPa; HDT 68 C at 1.8 MPa and 74 C at 0.45 MPa; Tg 68 C; Vicat 85 C. Note the sheet's descriptive text calls the filament a tough-PLA blend and Tg/Tm match that, so the body text looks like a copy-paste template; verify with Bambu. HDT below PETG-CF peak summer surface temperature.", "value": "Z 38 MPa; HDT 68/74 C", "source_url": "https://cdn.shopify.com/s/files/1/0380/5149/files/Bambu_PETG-CF_Technical_Data_Sheet.pdf" }, { "topic": "Datasheet PA6-CF", "fact": "Polymaker PolyMide PA6-CF datasheet versions disagree: V5.2 gives tensile XY about 81.7 MPa and Z about 64.4 MPa with Z elongation 2.5%; another version lists XY about 105 and Z about 67.7 MPa. Z modulus ranges 3760-4713 MPa across versions. HDT 173 C appears only on a retailer listing (unverified). Values are dry; PA6 is moisture-sensitive. Search-summary data.", "value": "Z about 64-68 MPa (dry)", "source_url": "https://www.3dprima.com/filament-resin/filament/nylon/polymaker-polymide-pa6-cf_28632_10303" }, { "topic": "Datasheet ASA", "fact": "Prusament ASA product page gives only heat resistance (no signs of deformation up to about 93 C) and 'UV stable'; no tensile, HDT, Z-axis or creep values on the page. Bambu's comparison table (retailer copy, search summary) lists ASA HDT 100 C and Z impact 4.9 kJ/m2 vs ASA-CF HDT 110 C and 9.4 kJ/m2.", "value": "ASA about 93-100 C", "source_url": "https://prusament.com/materials/prusament-asa/" }, { "topic": "Snap-fit retention (ABS)", "fact": "Abdul Manan and Osman Zahid 2025: 16 cantilever-hook models printed in ABS and tested on a universal testing machine against ANSYS; retention force from 1.722 N (Model 2) to 39.458 N (Model 5); insertion force from 3.34 N (Model 10) to 34.346 N (Model 13) in one listing, with a second listing giving 41.1 N maximum retention and 32.2 N maximum insertion; simulation to experiment error under 1.2-2.4% for the best models. Higher insertion and retention angles raised forces. Orientation not a variable.", "value": "1.7 to 41 N retention", "source_url": "https://journal.ump.edu.my/ijame/article/view/11091" }, { "topic": "Snap-fit design strain (assumption)", "fact": "A snap-fit calculator assumes allowable strain of 2% for PLA and 3% for PETG/ABS/ASA when the arm is printed flat, and half that when the arm stands along Z. These are design assumptions, not measurements. Guides generally advise printing hooks flat so bending acts along the layers.", "value": "2% PLA, 3% PETG/ABS/ASA (flat)", "source_url": "https://buildcad.ai/snap-fit-3d-printing" }, { "topic": "Pin bearing strength", "fact": "Khosravani 2023, FDM double-shear pin-bearing coupons in PLA and ABS: highest fracture load 3646 +/- 143 N (ABS, W/D = 3); highest ultimate bearing strength 189 +/- 5 MPa (ABS, 3 mm hole); low W/D failed by cleavage, W/D 9 and 12 by bearing. Print orientation not varied; values from search summary (page 403 on fetch).", "value": "up to 3.6 kN fracture; 189 MPa bearing (ABS)", "source_url": "https://mdpi.com/2073-4360/15/7/1660" }, { "topic": "Printed draw latch load", "fact": "MakerWorld printed draw latch (0.2 mm layers, 3 walls, 15% infill): a 5-gallon jar of about 42 lb (about 187 N) did not break it. The designer notes pull force rises with the gap between the latch halves. This is a lower bound, not a rated or sustained value.", "value": "at least 187 N, no failure", "source_url": "https://makerworld.com/en/models/2266330-draw-latch" }, { "topic": "Toggle latch gasket", "fact": "MakerWorld self-locking toggle latch uses steel pins for reinforcement and recommends a roughly 2 mm elastic gasket to stabilise the clamping force; a test bench fixture is included but no force values were visible.", "value": "2 mm elastic gasket, steel pins", "source_url": "https://makerworld.com/zh-tw/models/1054989-self-locking-toggle-latch" }, { "topic": "Toggle clamp formula", "fact": "Engineering explainer models clamp force as hook stretch x hook spring rate, with an example of k = 200 N/mm and 1.5 mm stretch giving 300 N. Illustrative only, not test data.", "value": "300 N example", "source_url": "https://www.firgelliauto.com/blogs/mechanisms/toggle-latch" }, { "topic": "Cam-clamp metal benchmark", "fact": "An ELESA catalogue lists a metal cam clamp (LAC.44) with maximum clamping force 3500 N. This is a catalogue rating for a steel part, useful only as a scale reference; no printed cam-lever force data was found.", "value": "3500 N (metal)", "source_url": "https://docs.rs-online.com/df90/A700000013422799.pdf" }, { "topic": "Epoxy-bonded latch casing (adhesion limit)", "fact": "UW Midsun test of 3D printed latch casings bonded to carbon fibre with epoxy under a 200 lb pull: PETG held 82 lb before the whole print came off (poor epoxy bond), resin held 100 lb (test maximum). Measures the bond, not the plastic.", "value": "PETG 82 lb bond", "source_url": "https://uwmidsun.atlassian.net/wiki/spaces/MECH/pages/3382248051/3D+print+latch+casing+test" }, { "topic": "Own calculation: peak to sustained at SF 2", "fact": "Own calculation, safety factor 2 only (no creep/heat derate, because none is measured): M3 PETG insert 1.17 kN gives about 580 N; M3 PETG direct screw 1.16 kN gives about 580 N; bottom-pocket nut 1.63 kN gives about 810 N; side-pocket nut 0.84 kN gives about 420 N; flat ASA hook 559 N gives about 280 N; standing ASA hook 167 N gives about 83 N (196 N, about 98 N in a 30 C enclosure); flat PETG hook 540 N gives about 270 N; standing PETG hook 245 N gives about 123 N; PC Blend flat hook about 740 N gives about 370 N; ABS snap-fit about 40 N gives about 20 N. Hook figures are for CNC Kitchen's own geometry only.", "value": "see fact", "source_url": "https://cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament" }, { "topic": "Own calculation: sun surface temperature vs material limits", "fact": "Own interpretation: an enclosure surface of 60-70 C in sun sits at or above PETG's HDT (75-78 C Polymaker, 68-74 C for PETG-CF) and close to its Tg (81 C; PETG-CF 68 C), so a PETG latch loaded at 60-70 C is at risk of creep. ASA (heat resistance about 93-100 C), PC (HDT 107-110 C, Tg 115 C) and PC-CF have margin. In Dogan 2022, ABS ruptured in about 3 min at 60 C and 20 MPa while PC did not.", "value": "PETG marginal; ASA/PC preferred at 60-70 C", "source_url": "https://wiki.polymaker.com/polymaker-products/more-about-our-products/documents/technical-data-sheets/petg-pet/polylite-tm-petg" }, { "topic": "Own calculation: steel hardware is never the limit", "fact": "Own calculation from ISO 898-1 stress areas (M3 5.03, M4 8.78, M5 14.2 mm2) and class 8.8 proof stress 580 MPa: proof loads about 2.9, 5.1 and 8.2 kN. These are 2.5-7 times higher than the measured PETG M3 insert/screw pull-out (about 1.2 kN), so the printed boss or lug sets the latch's capacity.", "value": "M3/M4/M5 proof about 2.9/5.1/8.2 kN", "source_url": "https://www.cnckitchen.com/blog/helicoils-threaded-insets-and-embedded-nuts-in-3d-prints-strength-amp-strength-assessment" } ] }, { "key": "gasket", "summary": "GASKET-ENGINEER RESULT. Bottom line: the force each latch must deliver is set mainly by the gasket cross-section you print, not by IP rating. A solid 3 x 3 mm 85A TPU bead is very stiff. Over a 700 mm path on a 200 x 150 mm lid it needs about 2.9 kN at a bare sealing threshold (~7% squeeze), about 6.5 kN at 15% and about 11.6 kN at 25%. With 6 latches that is about 480 N, 1.1 kN and 1.9 kN per latch (own calculation from the Texin 985 85A TPU ASTM D575 curve). A narrow printed rib (1.2 x 2.4 mm) or a hollow/low-infill bead needs only about 1.2-3.6 kN total (about 200-600 N per latch with 6 latches). A 1 mm rib pressing into a flat gasket needs about 2.8-6.3 kN (rough estimate). Recommended design target: gasket line load of about 2-4 N/mm (about 1.4-2.8 kN on the reference lid), 20-25% initial squeeze, and a positive hard stop at every latch. That makes a realistic latch requirement about 250-600 N sustained per latch with 6 latches. Latches rated far above that only pay off if you insist on a solid wide bead.\n\nFour other findings:\n- Sealing pressure: Garlock says most elastomer gaskets seal at about 200 psi (1.4 MPa) assembly stress. On the TPU curve that is only about 7% squeeze (0.2 mm on a 3 mm bead). IP67 water head (1 m, about 10 kPa) is negligible against that. Leaks come from FDM surface and layer-line leak paths, not from water pressure.\n- Compression set: BASF Ultrafuse TPU 85A shows 26% set at 23 C and 52% at 70 C (ISO 815). Squeeze therefore roughly halves after hot sun. Start at 20-25% so at least 10-12% remains, and keep 0.2 mm or more of absolute squeeze (Parker's minimum).\n- Flange stiffness is the real limiter on latch count. Mid-span bow is w*L^4/(384*EI) for a continuous rim (own calculation). With w = 3.7 N/mm and a 0.15 mm bow allowance, a flat 3 mm lid edge only allows about 30 mm pitch. A 3 mm plate plus 20 mm deep skirt allows about 110 mm. A 30 mm deep box rim allows about 150 mm. In most cases a stiffer rim is cheaper than a stronger latch.\n- Material and temperature: Prusament lists PETG at 68 C and ASA at 93 C temperature resistance, so PETG is marginal for a sustained-load latch or flange at 60-70 C sun. TPU stiffens in the cold, about 2.2x higher flexural modulus at -30 C than at 23 C (Texin datasheet), so closing force at a fixed stroke rises in winter.\n\nLimits and caveats:\n- Printed TPU gasket force-deflection data (infill, hollow, rib geometry) are not published. My printed-gasket numbers use molded Texin 985 data scaled by geometry and an assumed 0.4-1.0 infill factor. Measure on a force gauge before trusting them.\n- The WebSearch budget ran out near the end, so I could not source PETG/ASA moduli (I assume E = 1.8 GPa) or FDM sealing-face roughness.\n- Some Parker O-ring numbers come from search-result excerpts because the Parker page returned HTTP 403 on fetch. The Parker handbook force charts are images, so the O-ring cross-checks use the Lindley formula as given on a seal-vendor page.\n- Scratch text-extraction of downloaded PDFs was done only in the sandbox temp dir. No project files were created, edited or deleted.", "key_facts": [ { "topic": "required-force", "fact": "REFERENCE SCENARIO (own calculation). Lid 200 x 150 mm with a continuous gasket along the full lid perimeter, path length P = 2 x (200 + 150) = 700 mm (a gasket inset ~10 mm would be ~660 mm, about 6% less). Cross-section assumed: 3 mm wide x 3 mm tall SOLID 85A TPU bead, 100% infill, shape factor 0.5 (about the same as the 0.57 of the ASTM D575 specimen, which is 28.6 mm diameter x 12.5 mm thick per the standard). Force per length F' = sigma(strain) x 3 mm, with sigma taken from the Texin 985 (85A TPU) ASTM D575 compressive-load curve. Total closing force F = F' x 700 mm.", "value": "w = 3 mm, P = 700 mm", "source_url": "https://sushengpolymer.com/media/pdf/phFiH7_Texin-985.pdf" }, { "topic": "required-force", "fact": "Reference total closing force, LOW end (just above the Garlock rule-of-thumb sealing stress of about 200 psi = 1.4 MPa, which is 6.7% squeeze = 0.20 mm of a 3 mm bead): F' = 4.1 N/mm, total about 2.9 kN. This is a bare threshold with no margin for FDM roughness, flatness error or relaxation.", "value": "about 2.9 kN (F' 4.1 N/mm)", "source_url": "https://legacy.garlock.com/sites/default/files/documents/en/Gasket%20Assembly%20Stress%20Non-metallic%20-%20Aug%202022.pdf" }, { "topic": "required-force", "fact": "Reference total closing force, MID design point (15% squeeze = 0.45 mm; Texin 3.10 MPa at 15%): F' = 9.3 N/mm, total about 6.5 kN. At 10% squeeze (2.07 MPa): F' = 6.2 N/mm, total about 4.3 kN.", "value": "about 6.5 kN at 15% (about 4.3 kN at 10%)", "source_url": "https://sushengpolymer.com/media/pdf/phFiH7_Texin-985.pdf" }, { "topic": "required-force", "fact": "Reference total closing force, HIGH end (25% squeeze = 0.75 mm, the top of the 20-30% window recommended by KRAIBURG and Elasto Proxy; Texin 5.52 MPa): F' = 16.6 N/mm, total about 11.6 kN. At 20% squeeze (4.31 MPa): F' = 12.9 N/mm, total about 9.0 kN.", "value": "about 11.6 kN at 25% (about 9.0 kN at 20%)", "source_url": "https://sushengpolymer.com/media/pdf/phFiH7_Texin-985.pdf" }, { "topic": "required-force", "fact": "PER-LATCH CLOSING FORCE for the 3x3 mm solid bead on a 700 mm path, assuming perfectly even distribution (own calculation). Seal-threshold 2.9 kN: 4 latches = 724 N, 6 = 483 N, 8 = 362 N. 15% (6.5 kN): 4 = 1628 N, 6 = 1085 N, 8 = 814 N. 25% (11.6 kN): 4 = 2898 N, 6 = 1932 N, 8 = 1449 N. Add roughly 20-30% to corner and end-of-span latches for non-uniform load sharing (my assumption).", "value": "4/6/8 latches: 0.72/0.48/0.36 kN (low); 1.63/1.09/0.81 kN (15%); 2.90/1.93/1.45 kN (25%)", "source_url": "https://sushengpolymer.com/media/pdf/phFiH7_Texin-985.pdf" }, { "topic": "required-force", "fact": "ALTERNATIVE cross-section A (own calculation): narrow printed rib 1.2 mm wide x 2.4 mm tall (three 0.4 mm perimeters). Using Texin stress x width (conservative-high), 700 mm path: 7% squeeze 1.2 kN; 10% 1.7 kN; 15% 2.6 kN; 20% 3.6 kN; 25% 4.6 kN. At 15% squeeze per latch: 4 latches 651 N, 6 latches 434 N, 8 latches 326 N. At 20%: 905 / 603 / 453 N.", "value": "1.2-4.6 kN total; 6 latches: 200-770 N each", "source_url": "https://sushengpolymer.com/media/pdf/phFiH7_Texin-985.pdf" }, { "topic": "required-force", "fact": "ALTERNATIVE cross-section B (own rough estimate, low confidence, plus or minus a factor of about 2): 1 mm wide rigid rib pressing 1 mm into a 3 mm flat TPU gasket gives a line load of about 4-9 N/mm, so about 2.8-6.3 kN over 700 mm. Per latch: 4 latches 700-1575 N, 6 latches 470-1050 N, 8 latches 350-790 N.", "value": "2.8-6.3 kN total", "source_url": "https://sushengpolymer.com/media/pdf/phFiH7_Texin-985.pdf" }, { "topic": "required-force", "fact": "ALTERNATIVE cross-section C (own calculation): 3 mm round cord of 85A elastomer (E of about 14 MPa) via Lindley's formula, 700 mm path: 15% squeeze 2.15 kN; 20% 3.4 kN; 25% 5.0 kN. Per latch at 20% squeeze: 4 latches 845 N, 6 latches 564 N, 8 latches 423 N.", "value": "2.2-5.0 kN total", "source_url": "https://www.xmbestseal.com/info/how-to-calculate-rubber-seal-compression-force-103529791.html" }, { "topic": "required-force", "fact": "DESIGN CONCLUSION (own judgement): size the gasket for a line load of about 2-4 N/mm (about 1.4-2.8 kN on 700 mm). With 6 latches that is about 240-470 N closing force per latch; with 8 latches about 180-350 N. A latch that sustains about 500-600 N each (safety factor 2 applied on top) therefore covers a well-designed printed gasket. Solid wide TPU beads at 20%+ squeeze push the per-latch requirement above 1.5 kN and also exceed what a printed 70 x 35 x 30 mm latch can hold for months.", "value": "2-4 N/mm design line load; 6 latches = about 240-470 N each", "source_url": "own calculation (inputs: https://sushengpolymer.com/media/pdf/phFiH7_Texin-985.pdf)" }, { "topic": "compression-force-data", "fact": "Texin 985 (polyether TPU, Shore 85A, Covestro): ASTM D575 compressive load at 2% deflection 0.345 MPa, 5% 1.03 MPa, 10% 2.07 MPa, 15% 3.10 MPa, 20% 4.31 MPa, 25% 5.52 MPa, 50% 16.5 MPa. This is the best published compression-vs-squeeze curve found for an 85A TPU (molded, not FDM-printed).", "value": "2%:0.345 / 5%:1.03 / 10%:2.07 / 15%:3.10 / 20%:4.31 / 25%:5.52 / 50%:16.5 MPa", "source_url": "https://sushengpolymer.com/media/pdf/phFiH7_Texin-985.pdf" }, { "topic": "compression-force-data", "fact": "Texin 985 other properties: tensile stress 4.80 MPa at 50% strain, 5.50 MPa at 100%, 9.70 MPa at 300%; flexural modulus 26.9 MPa at 23 C and 59.0 MPa at -30 C; Bayshore resilience 45%.", "value": "flexural modulus 26.9 MPa (23 C) vs 59.0 MPa (-30 C)", "source_url": "https://sushengpolymer.com/media/pdf/phFiH7_Texin-985.pdf" }, { "topic": "compression-force-data", "fact": "BASF Ultrafuse TPU 85A (printed filament, TDS v2.5, ISO 527, conditioned): stress 7.2 MPa at 50% elongation and 8.7 MPa at 100% when printed flat (XY); 6.2 and 7.5 MPa when upright (ZX). Stress at break 34 MPa (XY) vs 10 MPa (ZX); elongation at break 600% vs 320%; tear strength 80 kN/m (XY), 18 kN/m (XZ on edge) and 30 kN/m (ZX). Shore A 85, density 1111 kg/m3, Tg -44 C.", "value": "XY 8.7 MPa @100%; ZX 7.5 MPa @100%; break stress 34 vs 10 MPa", "source_url": "https://www.dream3d.co.uk/wp-content/uploads/2022/12/Ultrafuse_TPU_85A_TDS_EN_v2.5.pdf" }, { "topic": "compression-force-data", "fact": "Compression test of 3D-printed Ultrafuse TPU 85A (Ultimaker 3, 100% fill, 10 mm dia x 10 mm cylinders, ISO 604 style, compressed 7 mm = 70% strain): mean peak force 2587 N with a circular fill pattern, 1759 N zig-zag, 1315 N lines (about 2x spread from print pattern alone); peak stress 32.9 MPa circular. Specimens recovered strongly after the test (spring-back, as reported).", "value": "1315-2587 N at 70% strain (78.5 mm2 area)", "source_url": "https://reference-global.com/2/v2/download/article/10.2478/aucts-2024-0004.pdf" }, { "topic": "compression-force-data", "fact": "Nace et al. 2021 (Rapid Prototyping Journal): 50x50x25 mm FDM TPU blocks with four infill patterns (concentric, cross, cross3D at 20% and 30%, gyroid at 5% and 8%), compression to 70% per ISO 3386-1. TPU stiffness increases with infill percentage; 2D patterns show elasto-plastic buckling of cell walls. The filament used was Shore 93A (not 85A), and the stress values are only in figures, not in the text.", "value": "qualitative; no numbers in text", "source_url": "https://emerald.com/insight/content/doi/10.1108/RPJ-07-2020-0155/full/html" }, { "topic": "compression-force-data", "fact": "Young's modulus of 85A: NinjaFlex 85A TPU lists 12 MPa (ASTM D638 as reported by an aggregator of manufacturer data), tensile strength 26 MPa, elongation 660%. The Gent relation (Wikipedia form) gives about 13 MPa for Shore 85A (my arithmetic: 0.0981(56+7.62336x85)/(0.137505(254-2.54x85))). Both agree with the small-strain stiffness implied by Texin (about 17 MPa effective at 2% for shape factor 0.57).", "value": "E of about 12-13 MPa", "source_url": "https://plahunter.pages.dev/data-sheets/ninjatek/tpu-ninjaflex" }, { "topic": "compression-force-data", "fact": "Gent relation as given on Wikipedia (Shore durometer): E (MPa) = 0.0981(56 + 7.62336 S) / (0.137505(254 - 2.54 S)), S = Shore A. Alternative log-linear fits give ~4 MPa for 85A, so the choice of formula matters; measured values (12 MPa NinjaFlex) side with the Gent form.", "value": "13.2 MPa at S = 85 (own arithmetic)", "source_url": "https://en.wikipedia.org/wiki/Shore_durometer" }, { "topic": "compression-force-data", "fact": "O-ring cross-check, Parker excerpts: 0.070 in cross-section at 20% squeeze needs roughly 9-25 lb/in for 90A and 5-18 lb/in for 70A; 0.103 in section about 9-18 lb/in; softer durometer can cut the required force by up to 50%. Converted (1 lb/in = 0.175 N/mm, own conversion): 90A 1.6-4.4 N/mm; 70A 0.9-3.2 N/mm. These are LINE-contact round sections and are much softer than a flat-topped bead.", "value": "90A: 1.6-4.4 N/mm; 70A: 0.9-3.2 N/mm (0.070 in, 20%)", "source_url": "https://www.parker.com/us/en/divisions/o-ring-and-engineered-seals-division/resources/seal-solutions-guide/improving-installation-radial/reducing-installation-force/low-durometer-o-ring.html" }, { "topic": "compression-force-data", "fact": "Apple Rubber: a 0.070 in, 50-durometer O-ring needs about 4.5-14 lb/in (0.8-2.5 N/mm, own conversion) for 20% compression. Parker notes the load for a given installation is a range, and that compression force drops only 10% (70-durometer) to 22% (90-durometer) from 24 C to about 126 C.", "value": "50A, 0.070 in, 20%: 4.5-14 lb/in", "source_url": "https://applerubber.com/hot-topics-for-engineers/forces-needed-to-compress-seals" }, { "topic": "compression-force-data", "fact": "Lindley O-ring compression-force formula quoted by a seal vendor: F = pi*D*d*E*(1.25 r^1.5 + 50 r^6), i.e. per length F' = E*d*(1.25 r^1.5 + 50 r^6) (r = squeeze ratio). Vendor modulus table: 50A 2.2, 60A 3.5, 70A 5.8, 80A 9.6, 90A 19.5 MPa. Worked example 70A, ID 50 mm, d 3.53 mm, r = 0.20 gives 395 N total (2.35 N/mm, matched by my check). Sanity check against Parker excerpt: 90A, d 1.78 mm, 20% gives 4.0 N/mm (Parker range 1.6-4.4 N/mm).", "value": "3 mm cord, E = 14 MPa: 4.8 N/mm at 20%", "source_url": "https://www.xmbestseal.com/info/how-to-calculate-rubber-seal-compression-force-103529791.html" }, { "topic": "contact-pressure", "fact": "Garlock gasket assembly stress rule of thumb (Aug 2022): most elastomeric gaskets will seal at about 200 psi (1.4 MPa) assembly stress; recommended assembly stress for elastomers (70 Shore A) is minimum 600 psi (4 MPa) and maximum 900-1200 psi (6-8 MPa). On the Texin curve 1.4 MPa corresponds to about 6.7% squeeze and 4 MPa to about 19% (own interpolation).", "value": "seal: 1.4 MPa; recommended min 4 MPa; max 6-8 MPa", "source_url": "https://legacy.garlock.com/sites/default/files/documents/en/Gasket%20Assembly%20Stress%20Non-metallic%20-%20Aug%202022.pdf" }, { "topic": "contact-pressure", "fact": "IP67 water head is tiny compared with sealing stress: 1 m of water = 9.81 kPa (own calculation, 1 m x 1000 kg/m3 x 9.81). A seal vendor recommends assembly contact pressure of 1.5-2x the fluid pressure. Even the 1.4 MPa threshold is more than 100x a 1 m head. Leakage in printed enclosures is therefore governed by surface conformance (roughness, layer-line leak paths, warp), not water pressure. IP67 = immersion up to 1 m for 30 min per IEC 60529 (standard definition, general knowledge).", "value": "9.81 kPa at 1 m", "source_url": "https://www.xmbestseal.com/info/how-to-calculate-rubber-seal-compression-force-103529791.html" }, { "topic": "contact-pressure", "fact": "A Rogers/PORON enclosure-gasket note: silicone at about 1.5 psi (10.3 kPa), 3.2 mm thick, leaks 1.5 mL/min at 12.7 mm width, 12 mL/min at 6.35 mm, and 47 mL/min at 3.2 mm. Narrow gaskets leak much more at low stress, an argument for a wide land or a second rib on a TPU gasket. Rogers also gives a CFD rule of thumb at 25% compression: under 10 psi is easy closure for plastic housings, 10-30 psi is balanced, over 30 psi is heavy-duty.", "value": "width 3.2 mm: 47 mL/min vs 12.7 mm: 1.5 mL/min", "source_url": "https://rogerscorp.com/blog/2025/the-mechanics-of-enclosure-seal-design-gap-spacing-cfd-and-compressibility" }, { "topic": "compression-percent", "fact": "Recommended compression for solid elastomer gaskets: Elasto Proxy gives 20-30% for most solid rubbers (40-50A: 20-25%, 60A: 25-30%, 70A: 30-35%, 80A: 35% maximum; 15% minimum for reliable seal; over 35% risks permanent deformation). Its plastic-enclosure page says 40% is ideal with a 10-15% minimum and 50% maximum (the two pages disagree; the plastic-enclosure figure looks like a sponge/foam guideline). No source gives a guaranteed compression for IP65/IP67.", "value": "20-30% solid (80A: up to 35%)", "source_url": "https://www.elastoproxy.com/how-much-compression-do-rubber-gaskets-require/" }, { "topic": "compression-percent", "fact": "KRAIBURG TPE gasket guidance: a nearly rectangular profile thicker than 2 mm compressed about 20-30% has proven advantageous; avoid copying round or multi-hump rubber profiles one-to-one; fine raised features lose shape through creep; standard service range about -40 to +80 C.", "value": "20-30% on near-rectangular profile over 2 mm", "source_url": "https://www.kraiburg-tpe.com/pl/node/1281" }, { "topic": "compression-percent", "fact": "Parker O-Ring Handbook (static seals): maximum recommended squeeze for most elastomers 30% (face seals often benefit at 30% because recovery is better); danger in going much beyond 30%; minimum squeeze for any seal about 0.2 mm (0.007 in) because very light squeeze quickly takes 100% set; gland fill 60-85% (optimum 75%), at least 10% void.", "value": "max 30%; min 0.2 mm absolute; fill 60-85%", "source_url": "https://nfc.arizona.edu/sites/default/files/2022-02/parker_o-ring_handbook.pdf" }, { "topic": "compression-percent", "fact": "Printed TPU gasket reference designs: a MakerWorld parametric enclosure uses a TPU gasket in a groove with compression stops, about 25% designed squeeze on a 1.2 mm gasket height, and states it is not independently tested or certified (read from search-result excerpts). A hobby Arduino enclosure sits its TPU gasket 1 mm into each half plus 0.5 mm of sealing height, 10% infill, 1 mm walls, screw-compressed, and passed a shower test (no measurements).", "value": "about 25% on a 1.2 mm gasket; 1.5 mm total protrusion", "source_url": "https://penguintutor.com/news/3d-design/weatherproof-3dprint" }, { "topic": "compression-percent", "fact": "Flat (uncontoured) gaskets: a Multicomp enclosure datasheet states a flat gasket reaches IP65 but will not reliably give IP67 (from search-result excerpt); a Core77 poster notes IP67 depends on rib and compression-element geometry. Stockwell warns cellular gaskets may not suit IP67/NEMA 6 submersion.", "value": "flat gasket: IP65; IP67 needs rib/bead geometry", "source_url": "https://elcodis.com/parts/2766367/MCGEC1_p2.html" }, { "topic": "compression-set", "fact": "BASF Ultrafuse TPU 85A TDS v2.5 (ISO 815): compression set 26% after 72 h at 23 C and 52% after 24 h at 70 C. Specimen type (printed vs molded) is not stated in the extracted sheet. By Parker's definition (percent of applied deflection not recovered) a 52% set means roughly half the original squeeze is gone.", "value": "26% (23 C, 72 h); 52% (70 C, 24 h)", "source_url": "https://www.dream3d.co.uk/wp-content/uploads/2022/12/Ultrafuse_TPU_85A_TDS_EN_v2.5.pdf" }, { "topic": "compression-set", "fact": "Texin 985 (molded 85A TPU): ASTM D395B / ISO 815 compression set 16% and 19% at 23 C / 22 h (two specimen conditions, footnotes not legible), and 40% and 80% at 70 C / 22 h. The wide gap at 70 C shows how sensitive TPU set is to specimen type and conditioning.", "value": "16-19% (23 C); 40-80% (70 C)", "source_url": "https://sushengpolymer.com/media/pdf/phFiH7_Texin-985.pdf" }, { "topic": "compression-set", "fact": "ROSA3D ROSA-Flex 85A filament TDS (ISO 815): compression set 29% and 42% (test temperatures not legible in extraction; likely 23 C and 70 C). Stratasys FDM TPU 92A (not 85A): 21% at 22 h/23 C and 44% at 22 h/70 C (ASTM D395, from search-result excerpt).", "value": "85A filament: 29% / 42%; 92A: 21% / 44%", "source_url": "https://www.lemona.lt/Files/Instrukcijos/Pdf/ROSA3D-TPU85%20TDS.pdf" }, { "topic": "compression-set", "fact": "Covestro: standard ester TPU grades show about 45-55% set at 24 h/70 C; special ester grades about 30-35%. Rule of thumb: flat seals should not exceed about 40% compression set at their continuous service temperature. Printed 85A TPU (52% at 70 C) is therefore at or beyond the limit in hot sun, so design for 20-25% initial squeeze so 10-12% remains.", "value": "limit about 40% at service temperature", "source_url": "https://solutions.covestro.com/en/highlights/articles/theme/product-technology/mechanical-properties-tpu" }, { "topic": "compression-set", "fact": "Remaining squeeze after set (own calculation, assuming ISO 815 style 25% deflection and set as percent of deflection): 26% set leaves 18.5% squeeze; 40% set leaves 15%; 52% set leaves 12%; 80% set leaves 5%. For a 3 mm bead that is 0.55 / 0.45 / 0.36 / 0.15 mm.", "value": "26% -> 18.5%; 52% -> 12%; 80% -> 5%", "source_url": "https://www.dream3d.co.uk/wp-content/uploads/2022/12/Ultrafuse_TPU_85A_TDS_EN_v2.5.pdf" }, { "topic": "compression-set", "fact": "Stress relaxation benchmarks (ISO 3384 style, 25% compression, 23 C, 24 h to 20,000 h): force loss under 25% is excellent for critical seals, 25-50% good, over 50% poor; many cheap elastomers lose over 50% in under 1 hour; loss gets worse at higher temperature. No TPU-85A-specific relaxation numbers were found.", "value": "under 25% excellent; 25-50% good; over 50% poor", "source_url": "https://rogerscorp.com/blog/2025/stress-relaxation-and-why-its-important-in-elastomeric-seals" }, { "topic": "compression-set", "fact": "Printed-gasket guidance (secondary source): compression set rises in printed elastomers with voids, weak interlayer bonding and uneven infill; set above 35-50% after heat aging (70 C, 22 h) leaks sooner than set below 20%; suggested remedies are 2-4 mm wall thickness and avoiding service above 60-80 C. This is commentary, not test data.", "value": "set above 35-50% leaks sooner", "source_url": "https://www.mfgrobots.com/Article/mfg/3dprinting/49001.html" }, { "topic": "temperature", "fact": "Cold raises closing force: Texin flexural modulus is 59.0 MPa at -30 C vs 26.9 MPa at 23 C (2.2x). Closing force at a fixed stroke at about -20 C may be up to roughly 1.5-2x the 23 C value (own inference from this ratio). Hot lowers force only a little: Parker found compression force of O-rings fell just 10% (70A) to 22% (90A) from 24 C to about 126 C. TPU softens and sets at 60-70 C; see compression set.", "value": "2.2x modulus at -30 C", "source_url": "https://sushengpolymer.com/media/pdf/phFiH7_Texin-985.pdf" }, { "topic": "temperature", "fact": "Prusament lists temperature resistance of 68 C for PETG and 93 C for ASA (the page does not say HDT or Vicat). With enclosure surfaces at 60-70 C in sun, PETG latch bodies and flanges sustaining kilonewton-level preload will creep; ASA has about 25 C more margin. Materials for the flange matter as much as the gasket here.", "value": "PETG 68 C; ASA 93 C", "source_url": "https://prusament.com/materials/prusament-petg/" }, { "topic": "printed-tpu", "fact": "Print orientation: Ultrafuse TPU 85A tear strength is 80 kN/m printed flat (XY) but only 18-30 kN/m when the loaded section is built on edge or upright, and break stress drops from 34 to 10 MPa. Print gaskets flat and keep thin ribs in the XY plane (rib along the layers), not as vertical standing walls.", "value": "XY tear 80 kN/m vs 18-30 kN/m", "source_url": "https://www.dream3d.co.uk/wp-content/uploads/2022/12/Ultrafuse_TPU_85A_TDS_EN_v2.5.pdf" }, { "topic": "printed-tpu", "fact": "Printed seal leak behaviour (anecdotal, not IP-tested): a Hackaday enclosure with a silicone-tube seal stayed dry for 10 min, then 2 h, and 12 h, but leaked a little at 24 h; the author notes molded plastics have no layer gaps. A forum thread reports roughness at the seal face causing leaks and suggests ironing the sealing surface and 0.1 mm layers (from search-result excerpt). Parker's static-seal guideline is 32 microinch (0.8 micrometer) Ra maximum and 16 microinch (0.4 micrometer) for gas face seals; as-printed FDM surfaces are far rougher (general knowledge, no source retrieved), so a soft TPU 85A or a flat-printed ironed land is needed.", "value": "Parker: Ra 0.8 micrometer static, 0.4 micrometer gas face", "source_url": "https://Hackaday.io/project/174011-water-resistant-3d-printed-enclosures" }, { "topic": "printed-tpu", "fact": "Printed TPU gasket guidance from a printed-gasket guide: 25% and 40% are common test deflections (25% is the ASTM D395 default); voids at 80-95% infill can cut effective cross-section 10-30%. Use 100% infill or walls only for gaskets, not low-density infill, if long-term set matters.", "value": "25% default; 10-30% effective area loss from voids", "source_url": "https://www.mfgrobots.com/Article/mfg/3dprinting/49001.html" }, { "topic": "flange-spacing", "fact": "Flange/cover theory: bolt (latch) spacing is limited by flange bowing between fasteners; spacing depends on cover thickness and stiffness (E*t^3), gasket width, and the ratio Pmax/Pmin of gasket pressure. Engineers Edge correction factors: Pmax/Pmin 2, 3, 4, 5, 6 -> 1.02, 1.00, 0.98, 0.95, 0.94 (spacing barely changes, under 7% from 3 to 6); Pmin 10, 20, 30, 40, 50 psi -> 1.19, 1.00, 0.90, 0.84, 0.80. The equations themselves are images and the calculator is paywalled.", "value": "Pmax/Pmin 3 -> 1.00; Pmin 20 psi -> 1.00", "source_url": "https://engineersedge.com/general_engineering/gasket_cover_compression.htm" }, { "topic": "flange-spacing", "fact": "Own calculation of maximum latch pitch L from continuous-beam bow delta = w*L^4/(384*EI), so L = (384*EI*delta/w)^0.25, with allowed bow delta = 0.15 mm (about a third of a 0.36-0.48 mm stroke), E = 1.8 GPa assumed. Simply-supported worst case is L = (384*EI*delta/(5w))^0.25 (about 33% shorter). Lid edge sections: 3 mm plate 10 mm wide (EI about 40 kN.mm2): 28 mm at w = 3.7 N/mm. With a 2.4 x 20 mm skirt (EI about 9300 kN.mm2): 110 mm at w = 3.7, 87 mm at w = 9.3. With a 3.2 x 30 mm rim (EI about 35,800 kN.mm2): 154 mm at w = 3.7, 122 mm at w = 9.3.", "value": "3 mm flat edge: about 22-28 mm; 20 mm skirt: 87-110 mm; 30 mm rim: 122-154 mm", "source_url": "own calculation (no external source; E = 1.8 GPa is an unsourced assumption)" }, { "topic": "flange-spacing", "fact": "Required EI for a given pitch (own calculation, continuous beam, bow 0.15 mm): at L = 120 mm, w = 1.7 N/mm needs about 6100 kN.mm2; w = 3.7 needs about 13,300; w = 6.2 needs about 22,300; w = 9.3 needs about 33,500 kN.mm2. At L = 90 mm the requirement is 4.1 times smaller (L^4 scaling). Gasket line load w is therefore as important as latch count: halving w roughly shortens the needed rim stiffness by half.", "value": "L=120 mm, w=3.7 N/mm -> EI about 13,300 kN.mm2", "source_url": "own calculation (no external source)" }, { "topic": "flange-spacing", "fact": "Beam-on-elastic-foundation check (own calculation): a 3x3 mm bead at 15% squeeze acts as a spring of about 20.7 N/mm per mm of stroke per mm length. For a flat 3 mm lid edge (EI about 40 kN.mm2) the characteristic length 1/lambda is about 9 mm, so a single latch only clamps about 30 mm (pi/lambda) of gasket; for a 30 mm box rim (EI about 35,800 kN.mm2) it clamps about 160 mm. This is the reason a flat thin lid cannot be sealed from a few latches.", "value": "clamped length pi/lambda: 30 mm (flat edge) to 161 mm (30 mm rim)", "source_url": "own calculation (no external source)" }, { "topic": "flange-spacing", "fact": "SAE 830216 (Oren): the maximum allowable bolt spacing for flange sealing occurs when midway pressure goes to zero; gasket compliance matters, and gaskets that can compress further beyond their sealing stress allow varying degrees of flange deflection while still sealing. Rogers adds that over-stiff gaskets can warp thin latching panels and enclosure covers.", "value": "qualitative", "source_url": "https://saemobilus.sae.org/papers/design-considerations-deflection-a-rigid-flange-gasket-joint-830216" }, { "topic": "design-rule", "fact": "Compression stop guidance: stops are cut shorter than the gasket thickness; keep at least one gasket-thickness of clear distance between the fastener hole edge and the stop edge; stops limit gasket damage and prevent excessive cover bowing from over-tightened fasteners. Own recommendation: one stop pair per latch at the latch line, plus stops at corners; stop height = (1 - 0.20 to 0.25) x free gasket height, e.g. 2.25-2.4 mm for a 3 mm bead.", "value": "stop height 2.25-2.4 mm for 3 mm bead", "source_url": "https://www.engineersedge.com/general_engineering/gasket_compression_stop.htm" }, { "topic": "design-rule", "fact": "Own calculation of latch stroke needed: a 3 mm bead needs 0.20 mm (7%), 0.30 mm (10%), 0.45 mm (15%), 0.60 mm (20%) or 0.75 mm (25%); a 2.4 mm narrow rib needs 0.17-0.60 mm. Total tolerance stack (FDM warp, hinge play) is of the same order, so latches need adjustability, an integrated hard stop, or a series spring. Parker's 0.2 mm minimum squeeze rule is met by every case above 7% on a 3 mm bead.", "value": "0.2-0.75 mm stroke", "source_url": "https://nfc.arizona.edu/sites/default/files/2022-02/parker_o-ring_handbook.pdf" }, { "topic": "design-rule", "fact": "Rogers: target 25-35% compression for foam-type enclosure gaskets, choose a gasket slightly thicker than the final gap, define minimum and maximum gap first, and avoid bottoming out; over-compression warps thin enclosures or even prevents closing. Stockwell: soft cellular gaskets may not suit IP67/NEMA 6; very firm gaskets create rebound forces that bow housings and open ingress paths.", "value": "25-35% (foam); account for gap tolerance", "source_url": "https://rogerscorp.com/blog/2025/the-mechanics-of-enclosure-seal-design-gap-spacing-cfd-and-compressibility" }, { "topic": "design-rule", "fact": "Summary of recommended gasket design for a printed enclosure (own judgement from the sources): 100% infill TPU 85A, printed flat, bead height at least 2 mm (KRAIBURG), width 1.2-1.6 mm, 20-25% initial squeeze, hard stop at each latch, groove leaving 10-25% void, ironed or smooth sealing land, flange with at least a 15-20 mm deep skirt, latch pitch under about 100 mm. Validate with a spray/immersion test and an elevated-temperature (60-70 C) hold; no published data certifies any printed TPU gasket to IP67.", "value": "w 1.2-1.6 mm; h at least 2 mm; 20-25% squeeze", "source_url": "https://www.kraiburg-tpe.com/pl/node/1281" } ] }, { "key": "outdoor", "summary": "Outdoor-materials findings for a printed latch holding a TPU 85A gasket (sun-heated surface 60-70 C, -20 to +40 C ambient).\n\n1. Heat is the main limit. Dark enclosures in sun reach about 67.6 C inside in a hobbyist test. PETG and PETG-CF have Tg about 68-80 C and HDT 68-74 C, so a sustained-load PETG latch sits at or above its HDT in hot sun. ASA (HDT about 92-103 C, Tg about 98 C), PC filament (HDT 99-114 C) and carbon-nylons (HDT 170+ C dry) have margin.\n\n2. Creep is the second limit, and the data are thin. The only multi-material FDM creep test I could read (3 h, 25/40/60 C, 10/20 MPa) found ABS ruptured in about 3 min at 60 C and 20 MPa. PLA broke at 60 C and 10 MPa. PC survived every condition. Nylon crept most but did not rupture. I found no published creep numbers for printed ASA or PETG at 60 C beyond 3 h, and none for sustained clamp loss of a printed latch with a TPU gasket. Treat all sustained-load design stresses for printed ASA/ABS-class parts as unvalidated. Keep them low (my judgement: at most 3-5 MPa at 60 C) and test.\n\n3. UV ranking:\n- ASA: essentially unchanged (within about 3% tensile) in 100 h of lamp exposure and in 1000 h of QUV.\n- PETG: mixed results, from +9% in a mild test to about -36% in a UV-B test.\n- Unstabilised PC: lost about 30-34% tensile strength and yellowed strongly in 1000 h of QUV.\n- Unstabilised PP: degrades in months.\n\n4. Moisture:\n- PA6-CF drops about 22-24% in strength and stiffness after conditioning at 70% RH. Equilibrium water uptake is 3.33%.\n- Unfilled PA6 loses about 69% of its modulus.\n- PA12-type PAHT-CF takes up 0.88% water, so it is the better nylon choice.\n\n5. Preload decay has three parts: gasket set, latch creep and thermal mismatch.\n- 85A TPU datasheets show 35-75% compression set at 70 C, with 35-52% typical. A rigid latch would lose roughly that fraction of gasket force (my calculation).\n- A spring 4 times softer than the gasket cuts the set-induced loss to about 20% of that (my calculation, formula in the facts).\n- A printed flexure loses at least the PC injection-moulded creep ratio of 14% per 1000 h at 23 C, and much more when hot.\n\n6. Latch types:\n- Tolerant of creep: designs where a steel spring, steel threaded link, steel wire or metal insert carries the preload. Examples are the spring-backed over-center lever, the adjustable threaded draw hook and the wire-bail latch.\n- Not tolerant: pure printed snap-fits, printed toggle levers and friction cams. That is my engineering inference, because no direct data exist.\n\n7. Hardware: use A2/A4 stainless pins, screws and springs. Zinc-plated steel is rated about 12-72 h (96-120 h for yellow zinc) in salt spray and is not suited to outdoor springs. Music wire rusts when wet.\n\nGaps and caveats:\n- The web-search budget ran out mid-task. Some values come from search summaries of datasheets I could not open (flagged in the facts).\n- No source gave printed-latch clamp force in newtons.\n- Vendor datasheet HDT values are for annealed, dry specimens.", "key_facts": [ { "topic": "Sun-heated enclosure temperature", "fact": "In a hobbyist test of sealed enclosures in direct sun, the black enclosure peaked at 67.6 C inside, the grey at 51.4 C, and the black one ran about 40 C above outside air. This supports the 60-70 C design temperature. Informal source, from a search summary; the page timed out when fetched.", "value": "67.6 C (black), 51.4 C (grey)", "source_url": "https://community.element14.com/challenges-projects/design-challenges/experimenting-with-extreme-environments/b/blog/posts/exploring-hidden-extremes-of-sheltered-environment---extra-blog-4--greenhouse-in-the-box" }, { "topic": "ASA heat resistance", "fact": "PolyLite ASA (Polymaker): Tg 97.8 C, Vicat 105.3 C, HDT 100.2 C at 1.8 MPa and 102.6 C at 0.45 MPa. Specimens were printed at 70 C ambient and the HDT is likely for annealed/standard test bars.", "value": "Tg 97.8 C; HDT 100.2 C @1.8 MPa", "source_url": "https://cdn.shopify.com/s/files/1/0603/6609/files/PolyLite_ASA_TDS_V5.1.pdf" }, { "topic": "ASA heat resistance (second brand)", "fact": "Bambu ASA V3.0: Vicat 106 C, HDT 92 C at 1.8 MPa and 100 C at 0.45 MPa, tensile strength 37 MPa XY and 31 MPa Z. The datasheet PDF no longer opened, so the values come from a search summary. Brand variation is therefore about 92-100 C at 1.8 MPa.", "value": "HDT 92 C @1.8 MPa", "source_url": "https://polyalkemi.no/wp-content/uploads/2024/01/Bambu_ASA_Technical_Data_Sheet.pdf" }, { "topic": "ASA injection-moulded reference (cold toughness)", "fact": "Luran S 757R (ASA, injection moulded): notched Charpy 3 kJ/m2 at -30 C, Vicat 98 C, HDT 97 C at 1.8 MPa (annealed). Low notch toughness at -30 C means ASA is notch-sensitive in cold weather, so avoid sharp corners in the latch. From a search snippet; the datasheet page would not open.", "value": "3 kJ/m2 notched Charpy at -30 C", "source_url": "https://materialdatacenter.com/ms/en/Luran/INEOS+Styrolution/Luran®+S+757R/a92c97e7/345" }, { "topic": "ASA anisotropy", "fact": "Printed PolyLite ASA: tensile strength 43.8 MPa (XY) versus 32 MPa (Z); elongation at break 6.7% (XY) versus 1.65% (Z); modulus 2379 MPa (XY) versus 1965 MPa (Z). Print the main load path along the layers (XY). Ratio Z/XY strength = 0.73 (my calculation).", "value": "43.8 MPa XY, 32 MPa Z", "source_url": "https://cdn.shopify.com/s/files/1/0603/6609/files/PolyLite_ASA_TDS_V5.1.pdf" }, { "topic": "PETG / PETG-CF heat resistance", "fact": "Bambu PETG-CF datasheet: Tg 68 C, Vicat 85 C, HDT 68 C at 1.8 MPa and 74 C at 0.45 MPa; water absorption 0.30%; tensile strength 59 MPa XY and 38 MPa Z (this is the V2-type sheet; a newer V3 sheet reportedly lists lower tensile values of 35 and 29 MPa). Carbon fibre does not raise heat resistance. A sun-heated latch at 60-70 C sits at or above this HDT.", "value": "Tg 68 C; HDT 68 C @1.8 MPa", "source_url": "https://cdn.shopify.com/s/files/1/0380/5149/files/Bambu_PETG-CF_Technical_Data_Sheet.pdf" }, { "topic": "PETG heat resistance (Prusament)", "fact": "Prusament PETG V0 (flame-retardant variant, so the standard grade may differ slightly): HDT 74 C at 0.45 MPa and 68 C at 1.8 MPa, tensile yield 39.4 MPa. A generic PETG datasheet gives Tg about 80 C and HDT 73 C at 0.45 MPa. Values come from search summaries.", "value": "HDT 68 C @1.8 MPa; Tg about 80 C (generic)", "source_url": "https://cdn.shopify.com/s/files/1/1745/6181/files/prusament-petg-v0-technical-data-sheet.pdf" }, { "topic": "PETG behaviour near 60 C", "fact": "An academic study of additively manufactured PETG found its time-temperature superposition creep method was limited by the 60 C test temperature, above which the material stopped behaving in a simply predictable way. In practice 60 C is already close to the PETG creep cliff. From a search summary; I did not read the paper.", "value": "limit of predictable behaviour about 60 C", "source_url": "https://opus.cloud1.lib.uts.edu.au/handle/10453/166023" }, { "topic": "PC filament heat resistance", "fact": "PolyMax PC (Polymaker): Tg 113 C, Vicat 116.9 C, HDT 99.3 C at 1.8 MPa and 114.1 C at 0.45 MPa (V5.1). The V5.4 sheet also lists 114 C at 0.45 MPa. Bulk injection-moulded Makrolon 2405 PC has Tg 144 C, so filament PC is typically a modified or blended grade with lower heat resistance. From search summaries.", "value": "Tg 113 C; HDT 99.3 C @1.8 MPa", "source_url": "https://polyalkemi.no/wp-content/uploads/2021/09/PolyMax_PC_TDS_V5.1.pdf" }, { "topic": "PA6-CF heat resistance (dry)", "fact": "PolyMide PA6-CF (Polymaker): Tg 74.2 C, melting 218.5 C, HDT 173 C at 1.8 MPa and 215 C at 0.45 MPa. Specimens were annealed at 80 C for 6 h and dried for 48 h before testing, so the HDT is for dry material. The Tg of 74 C is within reach of a hot enclosure, and moisture lowers stiffness (see moisture entries).", "value": "HDT 173 C @1.8 MPa dry; Tg 74.2 C", "source_url": "https://cdn.shopify.com/s/files/1/0548/7299/7945/files/PolyMide_PA6_CF_TDS_V5.2.pdf" }, { "topic": "PAHT-CF (PA12-type) heat and moisture", "fact": "Bambu PAHT-CF: Tg 70 C, melting 225 C, Vicat 220 C, HDT 170 C at 1.8 MPa and 194 C at 0.45 MPa, saturated water absorption 0.88% (25 C, 55% RH), tensile strength 92 MPa XY and 47 MPa Z (dry, annealed). Composition is PA12 and other long-chain PA plus carbon fibre. Z/XY strength ratio 0.51 (my calculation), so interlayer loading is a weak point.", "value": "HDT 170 C @1.8 MPa; 0.88% water", "source_url": "https://uwaterloo.ca/rapid-prototyping-centre/sites/default/files/uploads/documents/bambu_paht-cf_technical_data_sheet_v2.pdf" }, { "topic": "ASA UV weathering, lamp exposure", "fact": "Sedlak et al. 2023 exposed printed samples to a 125 W mercury lamp for 20 h and 100 h. After 100 h ASA tensile strength changed 0.0%, -1.6% and -2.9% (three brands, 44-46 MPa reference); ABS changed -0.9% to -2.3%; PETG rose +8.6% to +9.7% (49.5-49.9 MPa reference); PLA ranged -0.5% to +16.6%. Mild, short test, so useful for ranking only. Percent values were calculated from the paper's tables.", "value": "ASA -2.9% to 0%; PETG +8.6% to +9.7% (100 h)", "source_url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC10146359/" }, { "topic": "ASA UV weathering, 1000 h QUV", "fact": "Stratasys ASTM G154 QUV test, 1000 h (8 h UV at 60 C plus 4 h condensation at 50 C), upright ZX coupons: ASA yield strength 30.5 to 30.3 MPa (-0.7%), stress at break 30.5 to 29.5 MPa (-3%), modulus 1.82 to 1.95 GPa, elongation 2.8 to 2.3%; colour change minor (delta-E 0.9 on one plaque, 9.2 on the other, mainly lightening). Best option among the polymers tested for outdoor load-bearing.", "value": "ASA -0.7% yield, -3% break after 1000 h QUV", "source_url": "https://stratasys.com/siteassets/abm-pages/aerospace/wp_fdm_uv-aging_a4_0123a.pdf" }, { "topic": "Polycarbonate UV weathering", "fact": "Same Stratasys 1000 h QUV test: natural PC yield strength 6370 psi (43.9 MPa) to 4230 psi (29.2 MPa), about -34% (my conversion); stress at break 5940 to 4200 psi (-29%); elongation 3.0 to 1.6%; colour change delta-E about 33 (strong yellowing). PC-ABS lost about 4% in strength but delta-E was about 31. Unstabilised PC can lose a third of its Z strength in one season-equivalent of UV; use a UV-stabilised grade or paint/overmould.", "value": "PC -34% yield, -29% break, delta-E 33", "source_url": "https://stratasys.com/siteassets/abm-pages/aerospace/wp_fdm_uv-aging_a4_0123a.pdf" }, { "topic": "Nylon-CF UV weathering", "fact": "Stratasys FDM Nylon 12CF (carbon-filled nylon 12) had the smallest colour change of all materials in the 1000 h QUV test (delta-E about 0.7-0.8) and its tensile strength rose from 4760 to 6500 psi (about 33 to 45 MPa). ABS-CF10 lost about 4% in yield strength with delta-E about 5.3-5.8. TPU 92A lost about 15% in tensile strength (2730 to 2330 psi). Why nylon 12CF gained strength is not explained in the paper.", "value": "Nylon 12CF delta-E about 0.8; UTS +37%", "source_url": "https://stratasys.com/siteassets/abm-pages/aerospace/wp_fdm_uv-aging_a4_0123a.pdf" }, { "topic": "PETG UV weathering (mixed evidence)", "fact": "A 2026 QUV study of FFF-printed ASA, PETG and PLA found ASA kept ductility and showed improved strength, while PETG showed a moderate strength decrease with negligible change in elongation. A 2021 UV-B study (secondary summary) reported PETG tensile strength -36% and compression strength -38.3% after a 24 h cycle, against PLA -5.3% and -6.3%. A 1000 h UV study summary reported a modest increase for PETG. Results depend strongly on UV type and dose, so PETG outdoors is uncertain but ASA is consistently stable.", "value": "PETG -36% (UV-B, 24 h) vs +9% (mild lamp, 100 h)", "source_url": "https://mt.ujep.cz/artkey/mft-202601-0007_effect-of-accelerated-aging-on-the-mechanical-properties-of-fff-manufactured-polymers.php" }, { "topic": "PETG UV and creep", "fact": "In a flexural creep study of pellet-printed PETG, UV exposure (100 to 200 h) was the only stressor (compared with temperature and humidity) that increased creep compliance. Exact compliance values were not retrievable (paywall).", "value": "UV increased creep compliance", "source_url": "https://opus.lib.uts.edu.au/handle/10453/151771" }, { "topic": "Polypropylene outdoors", "fact": "A peer-reviewed study of unstabilised polypropylene films in Saudi Arabia found they degraded within 2.5 months of exposure. Unstabilised PP photo-oxidises (yellowing, chalking, embrittlement). Vendor claims of 40-60% tensile loss in 12 months are unverified. PP is not recommended for a load-bearing outdoor latch unless UV-stabilised or carbon-black filled.", "value": "unstabilised PP film degraded in 2.5 months", "source_url": "https://pure.kfupm.edu.sa/en/publications/development-of-polypropylene-based-ultraviolet-stabilized-formula/" }, { "topic": "Creep at 60 C, multi-material FDM test", "fact": "Dogan 2022 (ASTM D2990, 3 h tests, CNC-machined specimens, Ultimaker filaments, 25/40/60 C and 10/20 MPa): no rupture at 25 or 40 C for any material. At 60 C, ABS ruptured in about 3 min at 20 MPa, PLA and tough PLA broke at 60 C even at 10 MPa, and CPE broke at 60 C/20 MPa after a longer time. PC showed the lowest creep in every condition and never failed. Nylon crept most (the test was stopped when the micrometer ran out of range) but did not rupture. Load affected creep more than temperature.", "value": "ABS rupture about 3 min @ 60 C/20 MPa; PC no failure", "source_url": "https://ojs30.sv-jme.eu/index.php/sv-jme/article/download/191/118/2454" }, { "topic": "Creep ranking, carbon-fibre FDM", "fact": "Dimitrellou et al. 2024 (FDM, PLA vs PC vs PAHT-CF) found the highest stage-II creep resistance for PAHT-CF, followed by PC, then PLA. A separate 2024 Open Engineering study concluded that fibre reinforcement generally improves creep stability, with GreenTEC Pro Carbon and add:north PC Blend HT LCF performing best, and noted that most filament datasheets give no creep data. Numeric creep rates were not retrievable (paywall).", "value": "PAHT-CF > PC > PLA", "source_url": "https://link.springer.com/10.1007/s11665-024-09144-9" }, { "topic": "Creep data gap for open-source materials", "fact": "Open Engineering 2024 notes that most FDM filament datasheets include no creep behaviour and proposes a simple reproducible creep test. No source gave 100+ h creep data for printed ASA or PETG at 60 C. A vendor-style claim that PETG shows creep strain of 5% of its elastic strain within 5 h and 10% after 20 h at 50% of ultimate strength has no stated temperature or standard and is unverified.", "value": "no ASA/PETG 60 C long-term creep data found", "source_url": "https://www.degruyterbrill.com/document/doi/10.1515/eng-2024-0084/html" }, { "topic": "Polycarbonate creep modulus (injection-moulded reference)", "fact": "Makrolon 2405 PC: tensile creep modulus 2200 MPa at 1 h and 1900 MPa at 1000 h (ISO 899-1, 23 C), a retention of 0.86 (my ratio). Applied to a displacement-controlled printed flexure this implies about a 14% force loss in 1000 h at room temperature only. Much more loss is expected at 60 C. Bulk PC has Tg 144 C, higher than filament PC.", "value": "2200 to 1900 MPa (1 h to 1000 h, 23 C)", "source_url": "https://www.okw.ch/it/PC/RW_Makrolon_2405_en.pdf" }, { "topic": "Polycarbonate thermal expansion (mismatch with steel)", "fact": "Makrolon 2405 coefficient of linear thermal expansion 0.65e-4 per K (65e-6/K), 23-55 C. Own calculation with an assumed steel value of about 12e-6/K (handbook value, unsourced): over 60 K, a 30 mm plastic stack growing against a steel screw changes length by about 0.095 mm, about 13% of a 0.75 mm gasket deflection (3 mm gasket at 25%). ASA and PETG expansion values were not sourced here.", "value": "about 0.095 mm per 30 mm stack per 60 K (own calculation)", "source_url": "https://www.okw.ch/it/PC/RW_Makrolon_2405_en.pdf" }, { "topic": "Nylon moisture and stiffness (PA6-CF)", "fact": "PolyMide PA6-CF: equilibrium water absorption 3.33%. Dry, annealed XY specimens: modulus 7453 MPa and tensile strength 105 MPa. After conditioning at 70% RH and ambient temperature for 15 days: modulus 5666 MPa (-24%) and strength 81.7 MPa (-22%) (my percentages). Z-direction values changed little: modulus 4354 to 4713 MPa, strength 67.7 to 64.4 MPa (-5%). Charpy impact in XY rose from 13.3 to 32.8 kJ/m2.", "value": "XY strength 105 to 81.7 MPa; modulus 7453 to 5666 MPa", "source_url": "https://cdn.shopify.com/s/files/1/0548/7299/7945/files/PolyMide_PA6_CF_TDS_V5.2.pdf" }, { "topic": "Unfilled nylon 6 moisture stiffness loss", "fact": "A Unitika PA6 datasheet lists tensile modulus 2700 MPa dry-as-moulded versus 840 MPa conditioned at 23 C/50% RH (ISO 527), a drop of about 69% (my calculation), and tensile yield 68 to 42 MPa. Datasheet values from a search summary (the page text did not load).", "value": "2700 to 840 MPa; 68 to 42 MPa", "source_url": "https://knowde.com/stores/unitika/products/nylon-6-a1030tf" }, { "topic": "Nylon creep modulus and reinforcement", "fact": "BASF Ultramid B3K (unreinforced PA6) 1000 h tensile creep modulus (strain up to 0.5%, 23 C) is 700 MPa (conditioned figure only). Glass-filled PA6-GF30 grade B3WG6 GPX lists 4100 MPa. Reinforcement raises 1000 h creep modulus about 6 times. From search summaries of BASF datasheets; conditioning of the GF30 figure was not stated.", "value": "PA6 700 MPa vs PA6-GF30 4100 MPa at 1000 h", "source_url": "https://download.basf.com/p1/8a8082587fd4b608017fd637941722b5/de/ULTRAMID%25C2%25AE_B3K" }, { "topic": "Polycarbonate humidity and UV", "fact": "A study of unstabilised bisphenol-A polycarbonate found molecular weight falls during UV exposure (embrittlement and surface erosion) and that humidity accelerates photo-yellowing. Many filaments are not UV-stabilised. From a search summary.", "value": "not quantified", "source_url": "https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7962193/" }, { "topic": "TPU 85A compression set at 70 C", "fact": "Elastollan C85A55 (Shore 85A polyester TPU): compression set (ASTM D395B, 25% deflection, 22 h) is 25% at 23 C and 35% at 70 C. Tensile modulus 20.7 MPa, 100% modulus 6.89 MPa, hydrolytically stable. Other 85A grades at 70 C/22 h: 40% (ColorRx 85A0RX) and 43% (Elastane 4725-85A), and 75% for Estane 2355-85ABR. Ultrafuse TPU 85A (a printed-filament grade) lists 52% at 70 C/24 h and 26% at 23 C/72 h (ISO 815). Grade selection matters. Extruded or printed parts can be worse because of voids and weak layer bonding.", "value": "35% (70 C/22 h, Elastollan) to 52% (Ultrafuse); 75% worst", "source_url": "https://sushengpolymer.com/media/pdf/yKRdOr_Elastollan-C85A55.pdf" }, { "topic": "TPU 85A filament compression set", "fact": "BASF Ultrafuse TPU 85A TDS: compression set 26% at 23 C/72 h and 52% at 70 C/24 h (ISO 815). The 70 C value is about double the room-temperature value and is the one that matters for a sun-heated gasket. Taken from a search summary of the datasheet.", "value": "52% at 70 C/24 h", "source_url": "https://www.dream3d.co.uk/wp-content/uploads/2022/12/Ultrafuse_TPU_85A_TDS_EN_v2.5.pdf" }, { "topic": "Preload loss from TPU set with a rigid latch (own calculation)", "fact": "Own calculation from the datasheets above. Compression set is the unrecovered fraction of the applied deflection. If a creep-free rigid latch holds a linear gasket at a fixed gap and the gasket sets 35-52% (70 C datasheet range), the gasket force falls by roughly the same fraction, about 35-52%. This is a proxy: constant-strain stress relaxation of printed TPU was not found in any source and may be larger.", "value": "about 35-52% force loss (own calculation, upper-bound style proxy)", "source_url": "https://sushengpolymer.com/media/pdf/yKRdOr_Elastollan-C85A55.pdf" }, { "topic": "Preload loss with a series spring (own calculation)", "fact": "Own calculation. For a gasket of stiffness kg in series with a latch spring of stiffness ks, and a gasket set of S (fraction of its compression), the force loss fraction is S x ks/(kg+ks). With ks = kg/4 the loss is 0.2 x S: 7% for S = 35% and 10% for S = 52%. The spring needs about 4x the gasket compression travel (3 mm for a 0.75 mm gasket compression). With ks much larger than kg (rigid latch) the loss equals S.", "value": "ks = kg/4 gives 7-10% loss instead of 35-52%", "source_url": "https://sushengpolymer.com/media/pdf/yKRdOr_Elastollan-C85A55.pdf" }, { "topic": "Plastic joint clamp-load loss mechanism", "fact": "Creep or stress relaxation of plastic well below its elastic limit makes it lose its ability to maintain load, and the threaded connection loosens. Any thickness lost reduces screw clamp load, and the screw spring rate is so low that very little thickness change gives a loose joint. Metal threaded inserts are not susceptible to creep. No numeric percentage preload retention for printed or moulded polyamide joints was found.", "value": "qualitative", "source_url": "https://uk.spirol.com/assets/files/ins-wp-how-to-maintain-joint-integrity-when-converting-from-metal-to-plastic-us.pdf" }, { "topic": "Gasket stress relaxation in flange joints (analogue)", "fact": "In an industry article on bolted flange gaskets, ePTFE lost 12.6% of bolt stress in 20 h without retorquing, and a retorque 15 min after installation cut loss in spiral wound gaskets nearly in half, to 7.5%. This is a steel flange context, not TPU, but it shows loss is front-loaded. Taken from a search summary.", "value": "12.6% loss in 20 h (ePTFE); 7.5% after early retorque", "source_url": "https://www.pumpsandsystems.com/gasket-relaxation-importance-retorques-bolted-flange-joints" }, { "topic": "Corrosion of zinc-plated vs stainless hardware", "fact": "Fastener guide salt-spray ratings: electroplated zinc 12-72 h, yellow zinc (chromate) 96-120 h, hot-dip galvanised 500+ h, zinc-nickel 500-1000 h, Dacromet/Geomet 500-1000+ h. 18-8 (304/A2) stainless is general-purpose and 316 (A4) is recommended for marine, salt and chemical exposure; stainless needs no coating (passivated). Salt-spray hours are only a ranking aid, not outdoor life. For latch pins and screws outdoors use A2 (inland) or A4 (coastal/de-icing salt), not zinc-plated steel.", "value": "zinc plated 12-72 h; yellow zinc 96-120 h", "source_url": "https://www.albanycountyfasteners.com/media/48/29/31/1764608481/fastener-materials-and-coatings-guide.pdf" }, { "topic": "Spring materials outdoors", "fact": "Lee Spring: music wire may lose strength above 250 F (121 C), rusts in humid or wet conditions and often needs zinc/phosphate/powder coating. 302/304 stainless suits moisture, chemicals, wash-down and outdoor use and is rated about 550-600 F (288-316 C). Tensile strength: music wire above 400,000 psi in small sizes; 302/304 about 275,000-300,000 psi (so a stainless spring is about 25-30% weaker per wire size). No relaxation data for either material were found. The 316-grade statement (better in salt water) comes from a second spring vendor's page.", "value": "music wire 121 C max; 302/304 about 288-316 C max", "source_url": "https://www.leespring.com/music-wire-versus-stainless-steel" }, { "topic": "Belleville / disc springs vs creep", "fact": "A vendor white paper claims a Belleville washer can cut preload loss in a steel bolted joint to under 1% by adding elasticity. A flange-engineering source argues Belleville washers are not effective against high-temperature creep and that thermal cycling is the main failure mechanism there. A 2008 ASME paper found Belleville washers or longer bolts with spacer tubes can reduce load loss in flange joints. None of these is a plastic-joint test, so treat disc springs as helpful but unproven for printed hosts.", "value": "under 1% (vendor claim, steel joint)", "source_url": "https://www.solonmfg.com/documents/Combatting%20Embedment%20Relaxation%20in%20Bolted%20Joints%20-February%202025%20Final%20Version.pdf" }, { "topic": "Freeze / thermal cycling evidence", "fact": "Little quantified data was found for freeze-thaw or thermal cycling of printed latches. Known points: ASA (injection moulded Luran S 757R) has notched Charpy 3 kJ/m2 at -30 C, and PC Makrolon 2405 shows a puncture energy of 65 J at -30 C. ASA is therefore notch-sensitive in cold weather, and PC stays tough. Differential expansion over a 60 K swing is about 0.095 mm per 30 mm stack for PC vs steel (own calculation). No source gave PETG or nylon low-temperature impact data.", "value": "ASA 3 kJ/m2 notched at -30 C; PC puncture 65 J at -30 C", "source_url": "https://www.okw.ch/it/PC/RW_Makrolon_2405_en.pdf" }, { "topic": "Real-world outdoor test status", "fact": "A long-term outdoor filament test (eight common filaments including Polymaker ASA and Snapmaker PETG) was started in August 2025 by Finnish operator Ari Sovijarvi. No results were published as of my search. Vendor claims that PETG yellows after 3-6 months in sun and that ASA retains 85-90% property after 12 months are unverified.", "value": "no results yet", "source_url": "https://www.fabbaloo.com/news/real-world-outdoor-filament-test-launched-to-evaluate-3d-print-material-durability" }, { "topic": "Material recommendation summary (own judgement)", "fact": "Own judgement from the data above: ASA is the best default printed latch body (stable under UV, Tg about 98 C, HDT 92-103 C) but keep sustained printed-part stress low because ABS-class printed material ruptured at 60 C/20 MPa in minutes. PETG and PETG-CF (Tg about 68-80 C) should not carry sustained load in hot sun. PC is the best for creep and heat but needs a UV-stabilised grade. PAHT-CF (PA12-type, 0.88% water) is better than PA6-CF (3.33% water, -22 to -24% when wet). Avoid PP. Put the clamp preload in a stainless steel spring or screw regardless of the plastic.", "value": "ASA first choice; steel carries the preload", "source_url": "https://stratasys.com/siteassets/abm-pages/aerospace/wp_fdm_uv-aging_a4_0123a.pdf" }, { "topic": "Research limitations", "fact": "The web-search budget was used up before the cold-impact, thermal-expansion, corrosion-detail and insert-pull-out searches could be run. Several datasheet values (Bambu ASA, PolyMax PC, Prusament PETG V0, Unitika PA6, BASF Ultramid, Luran S 757R) come from search summaries because the PDFs or pages could not be opened. No source gave measured sustained clamp force or preload decay for a printed latch on a TPU gasket.", "value": "n/a", "source_url": "https://www.degruyterbrill.com/document/doi/10.1515/eng-2024-0084/html" } ] } ], "mechanisms": [ { "id": "oc-adjustable-screw-hook", "name": "Over-center draw latch with steel threaded adjuster (re-tensionable hook)", "working_principle": "A flat printed lever pivots on a stainless pin (P1) in a printed base. A second pin (P2), offset e = 10 mm from P1, carries a steel threaded link (DIN 444-type eye-bolt, or an M4/M5 screw with lock nut) that reaches the keeper on the lid. Closing swings P2 through dead centre (keeper-P1 line) to about 0.7 mm over-centre against a printed lever stop, so the hook load itself holds the lever shut and no friction is needed. Clamp force is set by take-up beyond gasket contact times the series stiffness of gasket and latch, not by hand force. The screw trims take-up to the 0.2-0.75 mm a TPU bead needs and re-tensions after compression set. The printed hook root is out of the load path; only printed pivot bores, base ears and the wall mount carry load.", "mechanical_advantage": "Lever 60 mm, eccentric e = 10 mm (own calc). Static MA at the lock position (phi about 4 deg, 0.7 mm over-centre) = L/(e sin phi) = 60/0.7, about 86:1. Worst point of the closing stroke (1 mm engagement stroke, M_max = 0.385 x F x e x phi_c): about 35:1 geometric, about 22:1 after pivot friction (mu 0.25 steel pin in ASA). Screw: M4 x 0.7 gives 0.7 mm of hook take-up per turn; 1/8 turn = 0.09 mm = about 51 N of clamp force at 587 N/mm series stiffness.", "peak_clamp_force_N": 700, "sustained_clamp_force_N": { "low": 170, "typical": 225, "high": 280 }, "limiting_factor": "Printed ASA, not the steel: bearing of the two 4 mm pin joints in printed bores and, first of all, bearing of the base screws in a 3-4 mm enclosure wall (2 x M4, 28 mm2). Thickening the mount pad to 6 mm moves the limit to the lever pin bore (about 290 N typical). All limits are ASA creep at 60-70 C, so sustained is roughly one third of peak.", "force_basis": "calculated", "calculation": "DIMENSIONS (my choice, inside 70 x 35 x 30): flat lever plate 9 mm thick (pin axes along Z, printed flat), handle 60 mm from P1, e = 10 mm, A4 stainless 4 mm pins in double shear, lug boss OD 14 mm, base = two ears 5 mm each with 25 mm root width and 12 mm standoff, steel M5 eye-bolt, base screwed to a 3.5 mm wall with 2 x M4.\nALLOWABLES (working rule from the brief, ASA at 60-70 C, safety factor already inside): in-plane net section 3 / 4 / 5.5 MPa; pin bearing 6 / 8 / 10 MPa; across layers 2 MPa (avoided by orientation).\nLIMIT CHECKS, low / typical / high:\n- lever bore bearing 4 x 9 = 36 mm2 -> 216 / 288 / 360 N\n- base ear bearing 2 x (4 x 5) = 40 mm2 -> 240 / 320 / 400 N\n- lever lug net section (14-4) x 9 = 90 mm2 -> 270 / 360 / 495 N\n- ear root in-plane bending, sigma = 6 x (F/2) x 12 / (5 x 25^2) = 0.0115 F -> 260 / 348 / 478 N\n- wall bearing under 2 x M4, 4 x 3.5 x 2 = 28 mm2 -> 168 / 224 / 280 N <- governs\n- A4 pins (2 x 12.6 mm2 shear), M5 eye-bolt and an M4 heat-set insert (PETG M3 insert pulls out at about 1.17 kN per the CNC Kitchen test) are all several times stronger and do not govern.\nResult: sustained 170 / 225 / 280 N. With a 6 mm pad (48 mm2) the lever bore governs: 216 / 288 / 360 N.\nPEAK (short-term break, 23 C): wall bearing 28 mm2 x about 25 MPa = 700 N; lever bore 36 x 28 = about 1.0 kN; lug 90 x 14 = about 1.26 kN. Report 700 N (500-1000).\nHAND FORCE: moment at the worst point = (1.72 F geometric + 1.0 F pin friction) mm = 2.72 F mm; at F = 225 N and a 60 mm lever that is about 10 N.\nFIT TO LOAD: 6 latches x 225 N = 1.35 kN on the 700 mm path = 1.9 N/mm (bottom of the 2-4 N/mm window); 8 latches = 1.8 kN = 2.6 N/mm. It cannot deliver the 467-700 N per latch a solid 3 mm bead needs.\nBENCHMARKS: Southco E8 plastic adjustable draw latch is rated 1560 N working load (from the brief, not re-fetched); DE-STA-CO 341 steel 2000 lbf with 0.76 in max hook adjustment (fetched); Camloc 95L 220 N working vs 445 N max (fetched); steel Ganter GN 850-500 5000 N. The printed version is 5-7x lower than injection-moulded GF nylon because ASA is weak across layers and creeps hot.\nEVIDENCE STATUS: no printed sustained test found; the web-search budget was exhausted in this run, so no new tests of this mechanism were located. Confidence low-medium.", "operating_force_N": 10, "preload_retention": "Rigid steel link: structure stiffness k_l about 2000 N/mm (assumed) in series with the gasket share k_g about 830 N/mm per 100 mm of pitch (own calc: 4 N/mm over a 0.48 mm squeeze x 100 mm). Set loss = s x k_l/(k_l + k_g) = 0.71 s. Ultrafuse 85A set 52 % at 70 C gives 37 % loss; 26 % at 23 C gives 18 %; Texin moulded 40-80 % at 70 C gives 28-57 %. ASA bearing creep of 0.02-0.05 mm adds 12-30 N (assumed; PETG bolted joints lost 11.5 % preload in 7 days vs 3 % for PLA, https://filamentspecs.com/creep-resistance-3d-printed-parts/). Cold: with 2.2x gasket modulus at -30 C the force at fixed stroke rises about 63 % (587 -> 955 N/mm). Expect about 55-65 % of the as-set preload after the first hot weeks if never re-tensioned; about 0.2 turn of an M4 (83 N / 587 N/mm = 0.14 mm) restores a 37 % loss. The steel link does not creep; use a lock nut or thread-lock.", "adjustable_preload": true, "positive_compression_stop": false, "scores": { "seal_suitability": 7, "outdoor_durability": 7, "printability": 8, "usability": 8 }, "best_materials": "ASA is the default (HDT 100 C, 1000 h QUV -3 % break stress). UV-stabilised PC probably raises the sustained limits about 1.3-1.5x (my judgement, unmeasured) and has the best creep margin. PETG and PETG-CF are marginal for sustained load at 60-70 C (HDT 68 C). PA6-CF is out (3.33 % water uptake, -22 % strength, -24 % modulus). PAHT-CF is acceptable but still creeps. Metal parts A4/A2 stainless.", "hardware": "Two A4 stainless 4 mm clevis or dowel pins (or M4 shoulder screws) with e-clips, one A4 DIN 444-type M5 eye-bolt (or M4/M5 screw) with a lock or nyloc nut and a 12 mm OD washer, a stainless 4 mm keeper pin or printed keeper ledge loaded in compression, 2 x M4 heat-set inserts (or screws with washers) for the base, optional compression spring. Flagged: this design depends on purchased hardware for the load path.", "design_guidelines": [ "Pin axes along Z; lever, link and base ears printed flat so every load is in the XY layer plane. Never load a hook root or ear across layers (ASA keeps only 29 % of flat strength in the CNC Kitchen hook test).", "4 mm A4 pins, bores printed at 4.2-4.3 mm; lever 9 mm thick, boss OD at least 14 mm (3.5x the pin), base ears 5 mm each, ear root at least 25 mm wide with a standoff of 12 mm or less.", "4-5 perimeters (1.6-2 mm wall) around every bore, 100 % infill in the lug and ear zones, 0.15-0.2 mm layers; internal fillets R 2 mm or more (ASA notched Charpy is only 3 kJ/m2 at -30 C).", "Over-center geometry: e = 10 mm, lock offset 0.6-0.8 mm (about 4 deg) against a printed lever stop; screw range at least 2 mm so one latch covers tolerance plus set.", "Add a printed hard stop beside every latch at 0.75-0.8x the free bead height so over-tightening cannot crush the gasket; adjust to the stop with the lock nut, not by feel.", "Mount pad on the enclosure at least 6 mm thick with two M4 inserts 25-30 mm apart; the wall bearing is the weakest link otherwise. Corner and end latches may see +20-30 % load.", "Use A4 hardware with anti-seize on the eye-bolt thread; re-tension about 0.2 turn after the first hot week and check yearly." ], "failure_modes": [ "Wall or ear bearing creep: the pin bores and screw holes slowly ovalise at 60-70 C, so preload drifts down and the lever eventually walks out of over-centre.", "Over-tightened screw crushes the TPU rib or cracks the ear root; cold makes it worse because the gasket force can be about 60 % higher at fixed stroke.", "Compression set of the 85A bead (up to 52 % at 70 C) loses 30-40 % of preload; without re-tensioning the enclosure weeps.", "Vibration or thermal cycling lifts the lever out of the over-center lock (Ganter notes shock and vibration reduce holding capacity); needs a lever stop and a positive catch.", "Stainless thread galling or seizure, or dirt fouling in the eye-bolt thread.", "Brittle cracking at sharp inner corners in ASA below -20 C." ], "existing_designs": [ { "title": "MakerWorld Self-Locking Toggle Latch 1054989", "url": "https://makerworld.com/en/models/1054989-self-locking-toggle-latch", "note": "closest printed starting point: 3 mm steel/stainless pins and a 2 mm TPU pad; fixed hook, no adjuster, no force data (carried from the brief, page not re-fetched, HTTP 403)" }, { "title": "M3 Toggle Latch High Performance (STLFinder)", "url": "https://www.stlfinder.com/model/m3-toggle-latch-high-performance-wkO8uZca/4063366", "note": "M3 hardware; claims more than 10 kg (about 98 N); no adjuster (carried from the brief, HTTP 403)" } ], "sources": [ { "title": "DE-STA-CO 341 draw latch", "url": "https://destaco.com/productdetails.341.html", "note": "fetched: 2000 lbf max holding capacity, 0.76 in max hook adjustment, 2.5 in draw movement" }, { "title": "Camloc 95L tension draw latches (EFC)", "url": "https://efc-intl.com/printitems/metal-access-fasteners/camloc-95l-series-tension-draw-latches", "note": "fetched: 220 N working load vs 445 N max, self-compensating spring-steel drawhook" }, { "title": "Southco E8 adjustable draw latches", "url": "https://southco.com/en_gb_int/E8", "note": "1560 N working load, about 7.9 mm adjustment; carried from the brief, page returns 403" }, { "title": "Ganter GN 850-500 (ehorst)", "url": "https://www.ehorst.de/en/Verschluss-Spanner-mit-Zuganker-GN-850-1-500-TG-mit-Gegenhalter-1398999.html", "note": "5000 N holding force; carried from the brief" }, { "title": "CNC Kitchen: comparing PLA, PETG and ASA (hook tests, oven test)", "url": "https://cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament", "note": "fetched: ASA hook lying 57 kg vs standing 17 kg; 30 C chamber 20 kg; ASA fails 120 C loaded" }, { "title": "CNC Kitchen: threaded inserts and embedded nuts", "url": "https://www.cnckitchen.com/blog/helicoils-threaded-insets-and-embedded-nuts-in-3d-prints-strength-amp-strength-assessment", "note": "M3 heat-set insert in PETG pulls out at 119 kg; carried from the brief, not re-fetched" }, { "title": "Texin 985 datasheet (85A TPU)", "url": "https://sushengpolymer.com/media/pdf/phFiH7_Texin-985.pdf", "note": "compression curve, set 40-80 % at 70 C, modulus 2.2x at -30 C; values taken from the brief" }, { "title": "Ultrafuse TPU 85A TDS", "url": "https://www.dream3d.co.uk/wp-content/uploads/2022/12/Ultrafuse_TPU_85A_TDS_EN_v2.5.pdf", "note": "compression set 26 % at 23 C, 52 % at 70 C; values taken from the brief" }, { "title": "Creep resistance of 3D printed parts (filamentspecs)", "url": "https://filamentspecs.com/creep-resistance-3d-printed-parts/", "note": "fetched: bolted PETG lost 11.5 % clamp force in 7 days vs 3 % for PLA; no ASA data" }, { "title": "Adjustable draw latch US 4540206", "url": "https://patents.justia.com/patent/4540206", "note": "threaded link in compression when latched; carried from the brief, page returns 403" } ], "review": { "id": "oc-adjustable-screw-hook", "verdict": "corrected", "peak_clamp_force_N": 600, "sustained_clamp_force_N": { "low": 130, "typical": 185, "high": 240 }, "scores": { "seal_suitability": 6, "outdoor_durability": 6, "printability": 8, "usability": 7 }, "issues": [ "The arithmetic reproduces to under 1 %: lever bore 36 mm2, base ears 40 mm2, lug 90 mm2, ear root coefficient 0.0115, wall 28 mm2, MA 60/1.72, series stiffness 587 N/mm, set loss 0.71 s, cold +63 %. The dispute is with the allowables and the omissions, not the maths.", "Lug net section and ear-root bending are checked at nominal stress with no stress concentration. A pin lug has Kt of about 2.5 and a filleted ear root about 1.5-2. With an effective Kt of only 1.5 they drop to 240 N and 232 N typical, within 5 % of the 224 N wall-bearing limit. Five failure modes then sit within about 1.4x of each other, so system capacity is below the single smallest limit.", "The keeper and lid-side path (keeper pin, ears, flange fixing) carries the same F but is never checked. The text says only the pivots, ears and wall carry load.", "Prying moment on the base is ignored. The pivot sits 12-15 mm off the wall, so F x 12-15 mm puts about 80-120 N of tension on one insert or screw at 185-225 N. The 'several times stronger' claim for inserts cites a 1.17 kN M3-in-PETG pull-out on flat coupons at room temperature. That is a peak value, not hot or sustained, and not ASA. Hot, sustained pull-out is probably 150-250 N, so the margin is about 1.5-2x, not several.", "Creep relaxation is assumed to be only 0.02-0.05 mm (12-30 N). If bearings and the lug sit at the working-rule stresses, about 1 % creep strain on a 15 mm lug alone is 0.15 mm, or about 90 N at 587 N/mm. 0.1-0.2 mm total (60-120 N) is more realistic, on top of the 37 % gasket-set loss. Scheduled re-tensioning is therefore mandatory, not optional. This does not change the capacity number but weakens the seal and durability scores.", "Hand force is overstated. The 1 mm engagement stroke belongs to a 587 N peak. At 225 N the stroke is 0.38 mm, giving geometric moment 1.07 F and about 8 N hand force. This is conservative and harmless.", "Camloc 95L: the page labels 445 N as tensile strength, not 'max load' (mild misquote). The Camloc is a stamped steel latch at 220 N working load, so a printed ASA latch matching it at 225 N sustained is optimistic.", "The US 4540206 patent (checked on Google Patents) describes a threaded link in compression when latched. The design here uses a tension eye-bolt, so the patent does not corroborate it, and it has no force numbers.", "A printed hard stop beside the latch does not relieve a rigid latch. Over-tightening against the stop still loads the printed parts past the allowable. The stop protects the gasket, not the latch.", "The E8 benchmark (1560 N, '5-7x lower') could not be fetched, so that comparison is unverified." ], "confidence": "low", "reviewer_notes": "Recomputed independently in Python. Limit-state results (low/typ/high, N): wall bearing 168/224/280, lever bore 216/288/360, ears 240/320/400, lug 270/360/495, ear root 261/348/478. These match the analyst. Pin bending (my addition): 534 N.mm at 225 N, about 85 MPa on a 4 mm A4 pin, so the pin is fine (about 3x margin on 316 yield). I then applied Kt 1.5 to lug and ear root (180/240/330 and 174/232/319), a 0.9 factor for several co-governing limits, and a 0.9 factor for the unchecked keeper side. The typical is then 224 x 0.81, about 185. The low and high are 130 and 240. The result is 18 % below the analyst, so this is a trim rather than a refutation. The sustained values rest on the brief's unvalidated ASA rule (3-5 MPa in-plane, 8-10 MPa bearing). Dogan 2022, which I decoded, used milled specimens for 3 h: ABS survived 10 MPa at 60 C and ruptured at 20 MPa in about 3 min. It supports the order of magnitude but not months of life. Peak is trimmed from 700 to 600 N because 25 MPa bearing on 4 mm screws in a 3.5 mm printed wall is the optimistic end. Hot-case caveat: gasket set and softening unload a rigid latch to about 0.5-0.6 of its as-set force, so the hot allowable is conservative for the initial assembly load. Cold +63 % force at fixed stroke is verified (2.2x modulus is in the Texin sheet). Scores: seal 7 to 6 (depends on maintenance re-tensioning and hits only the bottom of the 2-4 N/mm window at 6 latches). Durability 7 to 6 (no outdoor or creep test of this mechanism exists). Usability 8 to 7. Rank by delivered end-of-life force, assuming re-tensioning: the screw latch is first or second with the spring latch. The ranking is more robust than the absolute numbers, which are about +/-2x.", "dead_or_misquoted_sources": [ "https://southco.com/en_gb_int/E8 (HTTP 403 to automated fetch; the 1560 N and 7.9 mm figures are unverified)", "https://makerworld.com/en/models/1054989-self-locking-toggle-latch (HTTP 403; unverified)", "https://www.stlfinder.com/model/m3-toggle-latch-high-performance-wkO8uZca/4063366 (HTTP 403; the 10 kg claim is unverified)", "https://efc-intl.com/printitems/metal-access-fasteners/camloc-95l-series-tension-draw-latches (opens; 445 N is listed as tensile strength, not 'max load')", "https://patents.justia.com/patent/4540206 (403 on Justia; the Google Patents copy opens, shows a compression link, and has no force numbers)", "https://www.cnckitchen.com/blog/helicoils-threaded-insets-and-embedded-nuts-in-3d-prints-strength-amp-strength-assessment (opens and the numbers are right, but they are M3 in PETG on flat coupons, with wall thickness and temperature not stated; not valid as a hot, sustained, ASA margin)", "https://filamentspecs.com/creep-resistance-3d-printed-parts/ (opens; 11.5 % PETG vs 3 % PLA is right, but the page warns the figures are study-specific, gives no temperature, and has no ASA data)", "https://www.dream3d.co.uk/wp-content/uploads/2022/12/Ultrafuse_TPU_85A_TDS_EN_v2.5.pdf (PDF text not machine-readable here; set values 26 %/52 % not re-checked)" ] } }, { "id": "oc-fixed-hook-pinned", "name": "Over-center draw latch, printed body, steel pivot pins, fixed hook", "working_principle": "Printed lever, link and base pivot on 3 mm (or M4) stainless pins. The hook is a printed claw or a bent stainless-wire hook with fixed take-up. The lever swings through dead centre (keeper-P1 line) to about 0.5-0.7 mm over-centre and locks without friction. Clamp force is the fixed geometric interference times the series stiffness of hook, frame and gasket, so it scatters with every tolerance and falls as the TPU takes set. Pivot axes along Z, with lever, link and hook lying in the XY plane. A bent wire hook, or a 2 mm TPU pad between hook and mating side (MakerWorld 1054989), adds a little elasticity.", "mechanical_advantage": "Lever 60 mm, e = 10 mm, engagement stroke 1.5 mm (own calc, includes tolerance padding): geometric MA at the worst point = 60/2.11 = 28:1; about 21:1 after pin friction (3 mm pins, mu 0.25). Static MA at lock (0.6 mm over-centre) about 100:1. There is no adjuster: the hook force is whatever the interference gives.", "peak_clamp_force_N": 500, "sustained_clamp_force_N": { "low": 110, "typical": 155, "high": 210 }, "limiting_factor": "The printed hook neck (tension plus offset bending) and the 3 mm pin bearing in ASA at 60-70 C. A second weakness is not strength but scatter: with about 530 N/mm of series stiffness, 0.3 mm of tolerance moves the force by 160 N, as large as the allowable.", "force_basis": "calculated", "calculation": "DIMENSIONS (my choice): hook neck 12 mm wide x 8 mm thick (lying in XY), load line offset a = 3 mm from the neck centre line, inner fillet R 3 mm; lever plate 8 mm; 3 mm A4 pins (bearing 3 x 8 = 24 mm2); base on a 3.5 mm wall with 2 x M3 (3 x 3.5 x 2 = 21 mm2).\nALLOWABLES: net section 3 / 4 / 5.5 MPa; bearing 6 / 8 / 10 MPa (brief working rule).\nHOOK NECK: sigma = F/(t w) + 6 F a/(t w^2) = F/96 + 18 F/1152 = 0.0260 F. At 3 / 4 / 5.5 MPa: 115 / 154 / 211 N <- governs.\nPIN BEARING: 24 mm2 -> 144 / 192 / 240 N. WALL BEARING: 21 mm2 -> 126 / 168 / 210 N.\nResult: sustained about 110 / 155 / 210 N. If the offset grows to 6 mm the neck allowable drops to 70 N, so keep the load line in the neck.\nPEAK: neck at about 16 MPa nominal (37 MPa XY ultimate over Kt of about 2.3) = 615 N; pin 24 x 27 = 650 N; wall 21 x 25 = 525 N. Report 500 N (400-900 in the brief). Standing orientation: 29 % of lying (CNC Kitchen ASA hook 17 vs 57 kg), so about 150 N peak and about 45 N sustained, which is why orientation is a hard rule.\nHAND FORCE: (2.11 F geometric + 0.75 F friction) mm = 2.86 F mm; at 155 N and 60 mm that is about 7 N.\nFIT TO LOAD: 8 latches x 155 N = 1.24 kN = 1.8 N/mm (700 mm path) as set; after hot set (-33 %) about 830 N = 1.2 N/mm, below the 2-4 N/mm window.\nSCATTER: k_series = 1500 x 830/2330 = 534 N/mm (k_l = 1500 N/mm assumed); +/-0.3 mm of take-up gives +/-160 N, which is +/-100 % of the nominal 155 N.\nBENCHMARKS: Southco 37 lever-assist (GF nylon, stainless pins) 350 N clamping force, 475-520 N top variant (listings disagree; carried from the brief, datasheet copy could not be parsed); MakerWorld Draw Latch survived about 187 N but stretched out of position; M3 toggle latch claims above 10 kg.\nEVIDENCE STATUS: no printed sustained test found; the web-search budget was exhausted in this run. Confidence low-medium.", "operating_force_N": 7, "preload_retention": "Poor. k_l about 1500 N/mm vs gasket 830 N/mm per 100 mm pitch: set loss = s x k_l/(k_l + k_g) = 0.64 s, so 33 % at 70 C with Ultrafuse set 52 %, 17 % at 23 C (26 % set); Texin moulded set of 40-80 % at 70 C gives 26-51 %. ASA hook and pin creep adds about 0.03 mm x 534 N/mm = 16 N (10 %). Cold: +54 % at -30 C for the same stroke (534 -> 824 N/mm). Expect about 55-65 % of preload after the first hot summer and no way to restore it except by re-making the hook position (shims, slotted keeper). To end up with 110 N at end of life you must assemble at 165 N or more, which is already at the typical sustained limit. Not adjustable.", "adjustable_preload": false, "positive_compression_stop": false, "scores": { "seal_suitability": 4, "outdoor_durability": 7, "printability": 8, "usability": 8 }, "best_materials": "ASA default; UV-stabilised PC probably 1.3-1.5x higher sustained (my judgement). PETG and PETG-CF marginal at 60-70 C (HDT 68 C). PA6-CF avoid outdoors. Bent A4 stainless wire hook instead of a printed claw removes the weakest link and adds elasticity.", "hardware": "Two or three A4 stainless 3 mm pins (or M3/M4 shoulder screws) with e-clips, optional bent 2-2.5 mm A4 wire hook, optional 2 mm TPU support pad, 2 x M3/M4 heat-set inserts or screws with washers for the base, stainless keeper pin.", "design_guidelines": [ "Print lever, link and hook lying flat (pin axes along Z). Never print the hook standing: ASA keeps 29 % of lying strength.", "Hook neck at least 12 x 8 mm, load line within 3 mm of the neck centre line, inner fillet R 3 mm or more; or replace the claw by a bent A4 wire hook.", "3 mm pins give 24 mm2 of bearing; 4 mm pins with a 9 mm lever give 36 mm2 and about 40 % more load, so use 4 mm if the envelope allows.", "Give the keeper a slotted or stepped position (0.25 mm steps) so tolerance can be trimmed at assembly; add a printed hard stop beside each latch at 0.75-0.8x the free bead height.", "Add a steel series spring or accept that a 2 mm TPU pad carries its own 52 % compression set at 70 C. Do not count the TPU pad as the spring.", "4-5 perimeters, 100 % infill in lug zones, 0.15-0.2 mm layers, internal fillets R 2 mm or more.", "Wall pad at least 6 mm thick under the base with inserts, otherwise the 3.5 mm wall bearing (about 170 N typical) is the weakest link. Space latches at 100 mm pitch or less, with stiffened rim.", "Mark and check the set point after the first hot week; replace shims or hook if force has fallen." ], "failure_modes": [ "Fixed take-up scatter: a tolerance stack that is too tight crushes the rib or breaks the hook neck; too loose leaves the lid leaking.", "Compression set of the 85A bead (up to 52 % at 70 C) loses a third of the preload with no way to re-tension.", "Hook neck cracks from combined tension and offset bending, usually at the inner fillet, faster in cold ASA.", "Pin bore and screw hole creep ovalises the pivots at 60-70 C.", "Pin retention fails (e-clip lost) or the pin works out through vibration.", "Screw tearing out of the housing (designers report this as the usual printed-latch failure); wall count matters more than infill." ], "existing_designs": [ { "title": "MakerWorld Self-Locking Toggle Latch 1054989", "url": "https://makerworld.com/en/models/1054989-self-locking-toggle-latch", "note": "steel/stainless 3 mm pins and a 2 mm TPU pad; no force values (carried from the brief, HTTP 403)" }, { "title": "MakerWorld Draw Latch 2266330", "url": "https://makerworld.com/en/models/2266330-draw-latch", "note": "survived about 42 lb (187 N) without breaking but stretched out of position; lower bound only (carried from the brief, HTTP 403)" }, { "title": "M3 Toggle Latch High Performance (STLFinder)", "url": "https://www.stlfinder.com/model/m3-toggle-latch-high-performance-wkO8uZca/4063366", "note": "claims more than 10 kg (about 98 N) (carried from the brief, HTTP 403)" } ], "sources": [ { "title": "CNC Kitchen: comparing PLA, PETG and ASA (hook tests)", "url": "https://cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament", "note": "fetched: ASA hook lying 57 kg vs standing 17 kg (29 %); PETG 55 vs 25; PLA 73 vs 40" }, { "title": "Southco 37 series datasheet copy", "url": "https://static.chipdip.ru/lib/031/DOC015031575.pdf", "note": "350 N heavy-duty clamping force; carried from the brief, the PDF text layer could not be read here" }, { "title": "Southco 37 catalogue (Marek)", "url": "https://www.marek.eu/katalog-obrazku/produkt-8066/66871-37-l-en.pdf", "note": "475 N top variant; carried from the brief, the PDF text layer could not be read here" }, { "title": "MakerWorld Draw Latch 2266330", "url": "https://makerworld.com/en/models/2266330-draw-latch", "note": "42 lb test; carried from the brief" }, { "title": "Texin 985 datasheet (85A TPU)", "url": "https://sushengpolymer.com/media/pdf/phFiH7_Texin-985.pdf", "note": "set 40-80 % at 70 C, modulus 2.2x at -30 C; values taken from the brief" }, { "title": "Ultrafuse TPU 85A TDS", "url": "https://www.dream3d.co.uk/wp-content/uploads/2022/12/Ultrafuse_TPU_85A_TDS_EN_v2.5.pdf", "note": "set 26 % at 23 C and 52 % at 70 C; values taken from the brief" }, { "title": "Creep resistance of 3D printed parts (filamentspecs)", "url": "https://filamentspecs.com/creep-resistance-3d-printed-parts/", "note": "fetched: bolted PETG lost 11.5 % preload in 7 days vs 3 % for PLA" }, { "title": "CNC Kitchen: carbon fibre nylon PA6 vs PA12", "url": "https://www.cnckitchen.com/blog/carbon-fiber-nylon-in-3d-printing-pa6-vs-pa12-tested", "note": "fetched: M4 at 0.8 Nm for 1 week, PA6-CF needed re-tightening almost daily, ASA and PLA about once" } ], "review": { "id": "oc-fixed-hook-pinned", "verdict": "corrected", "peak_clamp_force_N": 450, "sustained_clamp_force_N": { "low": 70, "typical": 110, "high": 150 }, "scores": { "seal_suitability": 3, "outdoor_durability": 6, "printability": 8, "usability": 7 }, "issues": [ "The hook-neck calculation is a straight-beam formula with no stress concentration: sigma = F/96 + 18F/1152 = 0.0260 F (arithmetic correct). A claw hook is a curved beam with h/ri of about 4-5 at the throat, so the inner-fibre factor is near 2 and the fillet Kt adds to that. With an effective factor of 1.5 the neck allows 77/102/141 N, not 115/154/211. The printed claw governs at about 100 N.", "A bent A4 wire hook, which the analyst suggests, removes the neck limit. Capacity is then set by 3 mm pin bearing (144/192/240 N) and wall bearing (126/168/210 N), about 140-150 N after derating. This is a different design from the printed claw that was computed, so the typical should follow the printed claw.", "The Southco 37 benchmark is misfiled. The datasheet (chipdip copy, which I decoded) describes a flexible EPDM-rubber over-center latch with glass-filled nylon and stainless pins, nominal clamp force 110/190/350 N and 475 N for the top variant, rated -40 to 80 C. The rubber body is a series spring, so this supports the spring-backed class, not a rigid fixed hook. The '475-520 N' range is also off: 475 N is the top variant and 520 N appears nowhere.", "Delivered end-of-life force is the real issue. The as-set force decays to about 0.63 x as-set minus creep, so about 55-60 %. At 110 N as-set, 8 latches deliver about 520 N at end of life on a 700 mm path, which is 0.75 N/mm. That is far below the 2-4 N/mm design window. Seal score 4 to 3.", "Scatter of +/-0.3 mm gives +/-160 N at 534 N/mm. This is as large as the capacity, so one latch can crush the rib while its neighbour leaks. A hard stop only transfers that load into the latch. The stiff series spring or adjuster is not optional.", "The CNC Kitchen PA6/PA12 article does not give separate ASA and PLA re-tightening counts. It says only that PA12 needed one re-tighten, similar to PLA and ASA. The brief's claim is loosely supported.", "The 187 N Draw Latch result (MakerWorld 2266330) could not be fetched, and its material and 'stretched out of position' outcome mean it is a weak anchor." ], "confidence": "low", "reviewer_notes": "Recomputed: neck coefficient 0.0260 (matches); pin 3x8 bearing 144/192/240; wall 2xM3 21 mm2 126/168/210 (match); series stiffness 1500x830/2330 = 534 N/mm (match); set loss 0.52 x 1500/2330 = 33 % (match), cold +54 % (match). Hand force with the correct stroke at 155 N is about 4.3 N (analyst 7 N; conservative). The only substantive change is the missing Kt/curved-beam effect at the claw, which drops the governing limit from 154 N to about 102 N; I report 110 N typical (70-150), which includes a small credit for the wire-hook variant. Peak is trimmed from 500 to 450 N for consistency with the 20-25 MPa bearing peak used in the other mechanisms. The CNC Kitchen hook ratio (ASA 57 kg flat vs 17 kg standing, 29 %) and the PC Blend figures (74-77 kg flat, 22-35 kg standing) are verified. Scores: seal 4 to 3 (see end-of-life calc), durability 7 to 6 (no outdoor data), usability 8 to 7 (no adjustment, a tolerance-sensitive keeper).", "dead_or_misquoted_sources": [ "https://static.chipdip.ru/lib/031/DOC015031575.pdf (opens; text decoded here: 110/190/350 N nominal clamp, EPDM + glass-filled nylon + stainless pins, -40 to 80 C; the analyst said it could not be read)", "https://www.marek.eu/katalog-obrazku/produkt-8066/66871-37-l-en.pdf (opens; 475 N top variant verified; no 520 N value found)", "https://makerworld.com/en/models/2266330-draw-latch (HTTP 403; the 187 N claim is unverified)", "https://makerworld.com/en/models/1054989-self-locking-toggle-latch (HTTP 403; unverified)", "https://www.stlfinder.com/model/m3-toggle-latch-high-performance-wkO8uZca/4063366 (HTTP 403; unverified)", "https://www.cnckitchen.com/blog/carbon-fiber-nylon-in-3d-printing-pa6-vs-pa12-tested (opens; ASA and PLA re-tighten counts are not reported separately)", "https://www.dream3d.co.uk/wp-content/uploads/2022/12/Ultrafuse_TPU_85A_TDS_EN_v2.5.pdf (not machine-readable here; not re-checked)" ] } }, { "id": "oc-spring-loaded-compensating", "name": "Spring-backed over-center latch (steel spring in series; stored-energy or ratchet-stop gasket compensating)", "working_principle": "The same printed lever and pins as an over-center draw latch, but the closing load passes through a stainless coil spring, disc stack or spring-steel hook in series with the gasket. The spring is about 5x softer than the gasket, so compression set, thermal movement and plastic creep change the preload only slightly. Variants: a sprung carriage that follows an ageing gasket and is held by a toothed or ramped stop (ITW US 8376418); a stored-energy spring that is cocked on opening and pulls the lid in past the balance point (ITW US 9370294, a toggle arm holds the cocked spring and releases it over-centre); a self-compensating spring-steel drawhook (Camloc 95L). Needs about 3 mm of hook travel for about 0.5 mm of gasket squeeze and a hard stop beside the latch.", "mechanical_advantage": "Lever 60 mm, e = 12 mm, engagement stroke 2.5 mm (my calc, the spring needs the extra travel): geometric MA at the worst point = 60/2.98 = 20:1; about 15:1 after pin friction. Static MA at lock about 100:1. The force the user feels is spring rate x deflection: with the 175 N/mm spring below, 200 N needs 1.14 mm of spring deflection plus 0.24 mm of gasket squeeze.", "peak_clamp_force_N": 600, "sustained_clamp_force_N": { "low": 150, "typical": 200, "high": 250 }, "limiting_factor": "The same printed pivot and mount limits as the screw-adjusted latch (4 mm pins, 3.5 mm wall), reduced by about 10 % because the sprung carriage, guide ribs and spring housing take envelope and add stress raisers. The latch needs more stroke (about 3 mm) than the other types. The steel spring itself is not the limit.", "force_basis": "calculated", "calculation": "SPRING (own design): 302/304 or 316 stainless compression coil, wire d = 3.0 mm, mean diameter D = 11 mm, 3 active coils, G = 69 GPa (assumed). Rate k_s = G d^4/(8 D^3 Na) = 69000 x 81/(8 x 1331 x 3) = 175 N/mm. At 250 N: deflection 1.43 mm, Wahl factor K = 1.45 (index 3.67), shear tau = K x 8 F D/(pi d^3) = 376 MPa. Solid height 5 x 3 = 15 mm, so the free length is about 20 mm and the carriage stop is set at 1.8-2.0 mm of deflection (about 315-350 N cap). The cap protects the printed parts from over-closing. Confirm the allowable with the spring maker (stainless is 25-30 % weaker than music wire per Lee Spring).\nSERIES STIFFNESS: structure (hook, pins, ears, wall) k_l = 2000 N/mm (assumed) in series with the spring -> 161 N/mm; in series with the gasket (830 N/mm per 100 mm pitch) -> 135 N/mm. Take-up for 200 N: 200/135 = 1.5 mm; add 1.0 mm for set and tolerance, giving the 2.5 mm engagement stroke and about 3 mm of hook travel.\nPRINTED PARTS: same as the screw-adjusted latch, with a 7 mm lever (carriage and spring seat take the rest of the Z envelope): pin bearing 4 x 7 = 28 mm2 at 6 / 8 / 10 MPa -> 168 / 224 / 280 N; wall bearing 28 mm2 gives the same. Knock-down factor 0.9 for guide ribs and tooth roots -> sustained 150 / 200 / 250 N.\nPEAK: structure limited, about 600 N (wall 28 mm2 x 25 MPa = 700 N less the 0.9 knock-down and the carriage tab shear). In service the stop caps the load at about 330 N, so the latch runs with a safety factor of about 1.8 against break.\nHAND FORCE: (2.98 F geometric + 1.0 F friction) mm = 3.98 F mm; at 200 N and 60 mm that is about 13 N.\nFIT TO LOAD: 8 latches x 200 N = 1.6 kN = 2.3 N/mm, and after hot set (-8 %) 2.1 N/mm, inside the 2-4 N/mm window. 6 latches give 1.7 N/mm, so 8 or more latches (or higher spring preset where the lever allows) are needed.\nEVIDENCE STATUS: the patents give no force or stroke values; no printed test found. The web-search budget was exhausted in this run. Confidence low-medium.", "operating_force_N": 13, "preload_retention": "Best of the four. Set loss = s x k_eff/(k_eff + k_g) with k_eff = 161 N/mm (175 N/mm spring in series with a 2000 N/mm structure) against k_g = 830 N/mm: 8.4 % at 70 C with Ultrafuse set of 52 % (vs 37 % for the rigid steel link and 33 % for the fixed printed hook), 4 % at 23 C. Printed pivot creep of 0.03 mm costs 135 N/mm x 0.03 = 4 N (about 2 %). Cold: +10 % at -30 C for fixed stroke (135 -> 148 N/mm) vs +54-63 % for the rigid latches. Tolerance scatter of +/-0.3 mm moves the force +/-40 N (+/-20 %), against about +/-175 N (+/-78 %) for the rigid steel link. Stress relaxation of the stainless spring at 70 C is not quantified in my sources; assumed negligible next to gasket set.", "adjustable_preload": true, "positive_compression_stop": false, "scores": { "seal_suitability": 9, "outdoor_durability": 6, "printability": 6, "usability": 7 }, "best_materials": "ASA default for lever, base and carriage; UV-stabilised PC probably 1.3-1.5x sustained (my judgement). PETG/PETG-CF marginal at 60-70 C. PA6-CF avoid (water uptake, moves guide clearances). Spring 302/304 or 316 stainless, not music wire (rusts, though it is stronger and tolerates 121 C).", "hardware": "Stainless 302/304/316 compression spring or Belleville stack (about 175 N/mm, free length about 20 mm), 4 mm A4 pins, steel washer under the spring on a printed seat, A4 hook or eye-bolt, optional printed ratchet teeth, 2 x M4 inserts for the base. Flagged: the spring rate and cap travel need measuring on the finished part.", "design_guidelines": [ "Choose the spring about 5x softer than the gasket share (k_s about 0.2 x k_g, about 175 N/mm for a 100 mm pitch) so set loss falls to about 8 %.", "Provide about 3 mm of hook travel for 0.5 mm of gasket squeeze and a carriage stop at 1.8-2.0 mm of spring deflection so the printed parts cannot be over-loaded.", "Over-center: e = 12 mm, lock offset 0.8 mm, lever stop; the sprung carriage guide with 0.3 mm clearance, a bore 14.5 mm for an 14 mm OD spring, and drain/dirt holes.", "Put a steel washer between spring and printed seat; seat face at least 150 mm2 (about 1.7 MPa at 250 N).", "Ratchet-stop variant: teeth at 0.5 mm pitch printed in the XY layer plane with tooth roots filleted; allow a manual release.", "Printed hard stop beside each latch at 0.75-0.8x the free bead height.", "Same pivot rules as the screw latch: pins along Z, 4-5 perimeters around bores, internal fillets R 2 mm or more, 6 mm mount pad with inserts.", "Shield the spring from grit and ice with a printed hood; test at -20 C for sticking." ], "failure_modes": [ "Ratchet teeth or the sprung carriage jam with ice, grit or warped guides.", "Spring set or corrosion if non-stainless steel is used; stainless spring losing force at high stress.", "The latch over-travels past the cap: the carriage tab shears or the spring coil-binds and loads the printed parts directly.", "Pivot and wall bearing creep as in the screw latch, but the spring masks it for a long time, so the failure is silent until the lever stop wears.", "Insufficient travel: a stiff spring chosen for compactness gives back the 30-50 % set loss of a rigid latch.", "Stored-energy variant snaps shut on fingers and is harder to release in the cold." ], "existing_designs": [], "sources": [ { "title": "Stored energy gasket-compressing latch US 9370294 (ITW)", "url": "https://patents.google.com/patent/US9370294", "note": "fetched: spring cocked on opening, toggle arm holds it, released over-centre; no force, rate or travel numbers" }, { "title": "Gasket-compensating latch mechanism US 8376418 (ITW)", "url": "https://patents.justia.com/patent/8376418", "note": "spring-biased carriage with toothed stop; carried from the brief, page returns 403" }, { "title": "Camloc 95L tension draw latches (EFC)", "url": "https://efc-intl.com/printitems/metal-access-fasteners/camloc-95l-series-tension-draw-latches", "note": "fetched: self-compensating spring-steel drawhook, 220 N working vs 445 N max" }, { "title": "Southco A2/A7 over-center lever latches", "url": "https://southco.com/en_au_int/latches/compression-latches/lever-latches/a2a7-over-center-lever-latches", "note": "350 N clamp, EPDM, stainless pins; carried from the brief (search text, page 403)" }, { "title": "Camloc catalogue excerpt (Scribd)", "url": "https://www.scribd.com/doc/109459302/Camloc-Ram-h", "note": "self-compensating spring-steel drawhook line; carried from the brief" }, { "title": "Music wire versus stainless steel (Lee Spring)", "url": "https://www.leespring.com/music-wire-versus-stainless-steel", "note": "music wire rusts, tops out about 121 C; stainless 25-30 % weaker; carried from the brief" }, { "title": "Texin 985 datasheet (85A TPU)", "url": "https://sushengpolymer.com/media/pdf/phFiH7_Texin-985.pdf", "note": "set and modulus ratios taken from the brief" }, { "title": "Ultrafuse TPU 85A TDS", "url": "https://www.dream3d.co.uk/wp-content/uploads/2022/12/Ultrafuse_TPU_85A_TDS_EN_v2.5.pdf", "note": "52 % set at 70 C; value taken from the brief" } ], "review": { "id": "oc-spring-loaded-compensating", "verdict": "corrected", "peak_clamp_force_N": 550, "sustained_clamp_force_N": { "low": 120, "typical": 170, "high": 220 }, "scores": { "seal_suitability": 8, "outdoor_durability": 5, "printability": 6, "usability": 7 }, "issues": [ "The spring maths reproduces: k = 69000 x 81/(8 x 1331 x 3) = 175 N/mm, Wahl 1.449, tau = 376 MPa at 250 N, set loss 8.4 % versus 36.7 % for a 2000 N/mm rigid link, cold +10 % versus +63 %. Even with the tangent gasket stiffness at 15-25 % squeeze (about 1210 N/mm per 100 mm, not 830) the spring latch loses only about 6 %. The preload-retention advantage is real and does not depend on the ASA allowables.", "The solid-height stress is about 1.3 GPa (875 N), above any static allowable. The carriage stop at 1.8-2.0 mm deflection is a safety-critical part, and a printed stop that creeps would let the spring coil-bind and overstress itself. A steel stop, or a stop inside the printed load path with margin, is needed.", "Both patents are appliance door locks. US 8376418 positions its toothed stop with a solenoid and a bi-stable cardioid track, and US 9370294 has an electrical switch. Neither gives force, rate or travel numbers. The ratchet with manual release and the hand-cocked variants are the analyst's extrapolation. No printed precedent exists, so seal 9 to 8 and confidence stays low.", "The 0.9 knock-down is arbitrary and probably too kind. Under the same Kt and keeper-side omissions as the screw latch, plus the added guide, carriage-tab and spring-seat limit states, my chain gives 224 x 0.9 x 0.9 x 0.9, about 165-175 N. Whether the 14 mm OD spring, carriage and e = 12 mm lever fit in 70x35x30 is not demonstrated.", "Printed parts carry the full spring force continuously at 60-70 C, because there is no unloading from gasket set as in a rigid latch. The hot creep allowable is therefore the right design case, and the 200 N claim needs the lower figure.", "Exposed spring, sliding carriage and printed guide (0.3 mm clearance) are the parts most exposed to ice, grit and ASA warp. Durability 6 to 5.", "At 170 N sustained, 6 latches give 1.5 N/mm and 8 latches 1.9 N/mm on 700 mm. It still needs 8 or more latches to reach the bottom of the 2-4 N/mm window.", "Stored-energy variant: the lid can snap shut on fingers and is hard to release in cold. Not a force issue, but a usability negative." ], "confidence": "low", "reviewer_notes": "Independent recomputation: series stiffness 135 N/mm (match), take-up for 200 N 1.48 mm (match); tolerance scatter +/-0.3 mm = +/-40 N (match); hand force at 200 N with s_peak 1.48 mm and e = 12 mm = 2.30 F geometric + 1.0 F friction, about 11 N (analyst 13 N, within error). Spring stress 376 MPa at 250 N and 496 MPa at the 330 N cap are fine for 302/304 (Lee Spring: stainless 275-300 ksi vs more than 400 ksi for music wire, music wire rusts above 121 C and in humid air, verified). End-of-life delivered force: this latch keeps about 92 % of as-set, versus about 63 % for the screw latch before re-tension and 63 % for the fixed hook with no recovery, so it delivers the most force at end of life even though the structural caps are similar. Sustained is trimmed to 170 N (-15 %). Peak is trimmed to 550 N. It is the only mechanism whose key advantage (stiffness ratio) is a first-principles result, so its rank for seal is the most robust of the four. Absolute force is as uncertain as for the others. Lee Spring and the ITW patents (checked on Google Patents) support only the principle. The Southco 37 (EPDM body, 110-475 N nominal clamp, to 80 C) is verified and is the closest commercial analogue to a spring-backed latch.", "dead_or_misquoted_sources": [ "https://patents.justia.com/patent/8376418 (HTTP 403 on Justia; the Google Patents copy opens: solenoid-actuated bi-stable stop for an appliance door, no numbers)", "https://patents.google.com/patent/US9370294 (opens; appliance door with an electrical switch, no force, rate or travel values)", "https://southco.com/en_au_int/latches/compression-latches/lever-latches/a2a7-over-center-lever-latches (HTTP 403; the 350 N claim is unverified, although the Southco 37 sheet shows 350 N for another model)", "https://efc-intl.com/printitems/metal-access-fasteners/camloc-95l-series-tension-draw-latches (opens; 445 N is labelled tensile strength, not 'max load'; the self-compensating drawhook is confirmed)", "https://www.scribd.com/doc/109459302/Camloc-Ram-h (not checked)", "https://www.dream3d.co.uk/wp-content/uploads/2022/12/Ultrafuse_TPU_85A_TDS_EN_v2.5.pdf (not machine-readable here; the 52 % set is not re-checked)" ] } }, { "id": "oc-fully-printed", "name": "Fully printed over-center draw latch (assembled hooks-over-pivots or print-in-place)", "working_principle": "Lever, link and hook are all printed; the pivots are printed posts that C-shaped hooks snap over (assembled), or clearance-gapped joints printed in place. The lever passes dead centre and locks without friction, but clamping force depends on the elastic stretch of the printed hook and pivot posts. Light preload only: the 85A bead needs a stiffer path, and printed pivots creep and wear.", "mechanical_advantage": "Lever 50 mm, e = 8 mm, engagement stroke 1.0 mm (my calc): geometric MA at the worst point = 50/1.54 = 32:1; about 11:1 after friction (mu 0.35 printed-on-printed, 9 mm posts). Static MA at lock (0.5 mm offset) about 100:1. The load is limited by the printed posts, not by the MA.", "peak_clamp_force_N": 250, "sustained_clamp_force_N": { "low": 25, "typical": 60, "high": 95 }, "limiting_factor": "Bending of the printed pivot posts (in-plane 3-5.5 MPa, across layers only 2 MPa) and creep stretching of the C-hooks. The print-in-place version is further limited by small posts and 0.3-0.4 mm gaps.", "force_basis": "estimated", "calculation": "ASSEMBLED VERSION (my choice): integral posts d = 9 mm lying with the axis in the layer plane, supported by two ears 6 mm each with a 17 mm span, lever 12 mm, C-hook back wall 3 mm, ASA, 5 perimeters.\nPost bending: Z = pi d^3/32 = 71.6 mm3; M = F L/4 = 4.25 F mm; sigma = 0.0594 F. At 3 / 4 / 5.5 MPa (in-plane) the post allows 51 / 67 / 93 N. If the post stands (axis Z, bending across layers, 2 MPa): 34 N.\nPRINT-IN-PLACE posts d = 5 mm, span 10 mm: Z = 12.3 mm3, sigma = 0.203 F -> 15-27 N in-plane, 10 N standing (gaps and fused layers are not accounted for). Sustained estimate for the family: low 25 (PIP or standing post), typical 60, high 95 N.\nPEAK: C-hook opening and ear root, not post bending (post alone would carry far more): about 250 N (100-400). The MakerWorld Draw Latch survived about 187 N and stretched out of position, so it is a lower bound for PLA-class parts, and ASA sustained of about 0.27 x 187 = 50 N (ratio from the 4 MPa / 15 MPa nominal stresses above) matches the 60 N typical.\nHAND FORCE: (1.54 F geometric + 3.15 F friction) = 4.7 F mm; at 60 N and 50 mm that is about 6 N.\nFIT TO LOAD: 8 latches x 60 N = 480 N = 0.7 N/mm on a 700 mm path, a third of the 2 N/mm window. It only works at 30 mm pitch (60 N / 30 mm = 2 N/mm), roughly the rim-bending pitch of a flat 3 mm lid edge (28 mm), i.e. 20+ latches, or with a much narrower, softer rib.\nEVIDENCE STATUS: no sustained printed test found; the web-search budget was exhausted in this run, so the printed-latch values rest on the brief's anecdotes (Draw Latch, 187 N). Confidence low.", "operating_force_N": 6, "preload_retention": "Poor and uncertain. Printed latch structure k_l about 300 N/mm (assumed; the compliance is what lets the lever close): set loss = 0.52 x 300/(300 + 830) = 14 % at 70 C, 7 % at 23 C. The dominant loss is plastic creep of the C-hooks and posts, which is unquantified; the MakerWorld Draw Latch stretched out of position at about 187 N, and PETG bolted joints lost 11.5 % preload in a week. My estimate is 20-50 % loss in the first hot season. Cold: +17 % at -30 C (220 -> 258 N/mm). Not adjustable.", "adjustable_preload": false, "positive_compression_stop": false, "scores": { "seal_suitability": 2, "outdoor_durability": 5, "printability": 9, "usability": 6 }, "best_materials": "ASA first; UV-stabilised PC for the best creep and heat margin (my judgement, probably 1.3-1.5x). PETG is too soft hot (HDT 68 C) and creeps. PA6-CF is out for moisture; PAHT-CF acceptable but still creeps. Avoid unstabilised PP outdoors (months). 3 mm A4 steel pins to harden the pivots turn this into the fixed-hook latch.", "hardware": "None required. Optional 3 mm A4 pins to harden pivots (that makes it the pinned fixed-hook latch).", "design_guidelines": [ "Walls of at least 1.2 mm per wall class, 5 perimeters, ASA or PC, 0.15-0.2 mm layers, link and hook printed on their sides (in-plane loads).", "Posts at least 9 mm for assembled latches, lying with the axis in the layer plane; never standing.", "Print-in-place gap 0.3-0.4 mm for a 0.4 mm nozzle, widened to 0.5 mm outdoors for grit; expect lower strength than assembled.", "Internal fillets R 2 mm or more; thick C-hook back walls (3 mm or more); ears at least 6 mm.", "Keep the load in the back of the C-hook, not on the opening lips.", "Use only with a thin, soft rib or at 30 mm pitch or less; add a printed hard stop at 0.75-0.8x the free bead height.", "Upgrade path: drill for 3 mm A4 pins and turn the latch into the fixed-hook pinned version." ], "failure_modes": [ "C-hook lips open or stretch (the lever creeps out of dead centre) under months of load or a hot afternoon.", "Post shear or bending crack at the root, especially if printed standing or in cold ASA.", "Print-in-place joints fuse or bind, or grit and ice jam the gaps.", "Printed pivots wear and gain play, so the over-center offset is lost.", "UV embrittlement of thin sections in unstabilised materials (PC, PETG).", "Too little force for the gasket: weeps at 85A rib squeeze." ], "existing_designs": [ { "title": "MakerWorld Draw Latch 2266330", "url": "https://makerworld.com/en/models/2266330-draw-latch", "note": "survived about 42 lb (187 N) but stretched out of position (carried from the brief, HTTP 403)" }, { "title": "Sturdy print-in-place draw latch (Printables)", "url": "https://www.printables.com/model/130254-sturdy-print-in-place-draw-latch", "note": "designer says it is weaker than metal latches (carried from the brief, HTTP 403)" }, { "title": "Wider sturdy latch with optional reinforced mount (Printables)", "url": "https://www.printables.com/model/1388482-wider-sturdy-latch-with-optional-reinforced-mount", "note": "wider print-in-place variant (carried from the brief)" }, { "title": "MakerWorld Waterproof Latch Sealed Boxes, Print-in-Place 2435156", "url": "https://makerworld.com/models/2435156", "note": "5 mm walls; splash-proof without gasket, almost waterproof with TPU 95A, no test data (carried from the brief)" }, { "title": "Replacement for Pentair LXLATCH (STLFinder)", "url": "https://www.stlfinder.com/model/replacement-for-pentair-lxlatch-NuK4TAoL/5223236", "note": "original moulded latches broke after about 10 years in sun; reprint in ABS/PETG/PC (carried from the brief)" }, { "title": "MakerWorld Tough Case 2385298", "url": "https://www.makerworld.com/en/models/2385298", "note": "only printed-latch-plus-85A-TPU design found: PETG snap latches, no force or IP data (carried from the brief)" } ], "sources": [ { "title": "MakerWorld Draw Latch 2266330", "url": "https://makerworld.com/en/models/2266330-draw-latch", "note": "187 N lower bound; carried from the brief" }, { "title": "Sturdy print-in-place draw latch (Printables)", "url": "https://www.printables.com/model/130254-sturdy-print-in-place-draw-latch", "note": "carried from the brief; fetch returned 403" }, { "title": "Replacement for Pentair LXLATCH (STLFinder)", "url": "https://www.stlfinder.com/model/replacement-for-pentair-lxlatch-NuK4TAoL/5223236", "note": "field evidence: moulded latches lasted about 10 years in sun; carried from the brief" }, { "title": "CNC Kitchen: comparing PLA, PETG and ASA (hook tests)", "url": "https://cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament", "note": "fetched: ASA lying 57 kg vs standing 17 kg" }, { "title": "Creep resistance of 3D printed parts (filamentspecs)", "url": "https://filamentspecs.com/creep-resistance-3d-printed-parts/", "note": "fetched: bolted PETG lost 11.5 % preload in 7 days vs 3 % for PLA; no ASA data" }, { "title": "Ultrafuse TPU 85A TDS", "url": "https://www.dream3d.co.uk/wp-content/uploads/2022/12/Ultrafuse_TPU_85A_TDS_EN_v2.5.pdf", "note": "52 % set at 70 C; value taken from the brief" } ], "review": { "id": "oc-fully-printed", "verdict": "corrected", "peak_clamp_force_N": 200, "sustained_clamp_force_N": { "low": 15, "typical": 40, "high": 65 }, "scores": { "seal_suitability": 2, "outdoor_durability": 4, "printability": 8, "usability": 6 }, "issues": [ "The typical of 60 N relies on printed posts lying with their axis in the layer plane. That makes the lever, link and C-hook planes contain Z, so their loads, including lever bending along the arm, run across layers. This contradicts the analyst's own rule of pin axes along Z and loads in-plane. The self-consistent orientation (axis along Z) gives the analyst's own post figure of 34 N for a 9 mm post at 2 MPa (about 25 N with a root fillet), and about 10 N for a 5 mm print-in-place post. A realistic family typical is about 40 N.", "The 187 N Draw Latch result is the only anchor and could not be fetched. The material is unknown, and the model 'stretched out of position', so it was creeping or yielding at 187 N. The 0.27 ratio is derived from the same allowables, so the claim that it 'matches' 60 N is circular.", "At 40 N sustained, 8 latches give 320 N on 700 mm, which is 0.46 N/mm, about 4-8x below the 2-4 N/mm window. The pitch needed to reach 2 N/mm is 20 mm, which is not practical. It is unsuitable for 85A TPU ribs and only works with a very thin, soft bead.", "Printed-on-printed pivots at 60-70 C with mu 0.35 wear and ovalise, and an ASA print-in-place joint with a 0.3-0.4 mm gap tends to fuse or warp. Durability 5 to 4, printability 9 to 8.", "Peak 250 N is not supported by anything fetched. Across-layer post bending at about 12-15 MPa peak gives 200-250 N, and in-plane about 500 N. C-hook lips yield first. I report 200 N (100-350)." ], "confidence": "low", "reviewer_notes": "Recomputed: post section modulus 71.6 mm3, bending coefficient 0.0594 sigma/N, allowable 34/51/67/93 N at 2/3/4/5.5 MPa (matches). Print-in-place post (5 mm, 10 mm span) 10/15/20/27 N. Friction hand force 4.7 F mm / 50 mm lever gives about 5 N at 40 N, fine. Preload retention: kl 300 N/mm gives set loss 13.8 % at 52 % set, and cold +17 % (match), but creep of the C-hook is unquantified and likely dominates. The orientation conflict is the substantive correction, because the stated high-end values need in-plane loading of a post whose lever and hook cannot also be loaded in-plane. Hardware-free printing is the real advantage, but it cannot supply gasket force. Scores: seal stays at 2, durability 5 to 4, printability 9 to 8, usability 6 unchanged.", "dead_or_misquoted_sources": [ "https://makerworld.com/en/models/2266330-draw-latch (HTTP 403; the 187 N / 42 lb figure is unverified)", "https://www.printables.com/model/130254-sturdy-print-in-place-draw-latch (HTTP 403; unverified)", "https://www.printables.com/model/1388482-wider-sturdy-latch-with-optional-reinforced-mount (not fetched)", "https://makerworld.com/models/2435156 (not fetched)", "https://www.stlfinder.com/model/replacement-for-pentair-lxlatch-NuK4TAoL/5223236 (HTTP 403; the ten-year field note is unverified)", "https://www.makerworld.com/en/models/2385298 (HTTP 403; the PETG snap latch with 85A TPU gasket is unverified)", "https://filamentspecs.com/creep-resistance-3d-printed-parts/ (opens; the 11.5 % / 3 % figures are study-specific, with no ASA data and no temperature)", "https://www.dream3d.co.uk/wp-content/uploads/2022/12/Ultrafuse_TPU_85A_TDS_EN_v2.5.pdf (not machine-readable here; not re-checked)" ] } }, { "id": "bail-wire-latch", "name": "Stainless wire bail latch with printed retainers", "working_principle": "A bent 304/316 stainless wire bail pivots in two printed holders on the base. Its short arm forms an over-center cam that drops into a printed catch on the lid. The wire flexes elastically as the bail goes over center. That flex is the clamp force, so the energy is stored in steel and not in plastic. Force is set by wire deflection, so it is spring-controlled and self-limiting. It is not stroke-controlled. Printed parts only hold the wire ends and form the cam seat and catch, and they see a low stress of about 3 MPa.", "mechanical_advantage": "Handle-to-cam lever ratio about 3:1 (45 mm handle, 15 mm cam arm), plus over-center holding. The clamp force is NOT hand force x lever ratio. It is wire stiffness x deflection, about 53 N/mm per leg for 3 mm wire with a 35 mm free length. The lever ratio only sets how little hand force is needed.", "peak_clamp_force_N": 250, "sustained_clamp_force_N": { "low": 25, "typical": 60, "high": 120 }, "limiting_factor": "Wire bending stiffness and allowable stress in a package that fits the 70x35x30 mm envelope. Bail legs of 3 mm wire and 25-35 mm length cap out at about 120-170 N. Beyond that the printed holder or catch breaks, or the wire takes a set. It is not a latch for a 1.4-2.8 kN lid unless there are 25-45 of them.", "force_basis": "estimated", "calculation": "NO MEASURED DATA: the web-search tool refused new searches (budget exhausted) and the printable-model pages returned HTTP 403, so this is a first-principles estimate. ASSUMPTIONS: 304 spring-temper wire, d = 2-3 mm. UTS at 2.5-3 mm is assumed ~1,500-1,700 MPa (own value). Lee Spring only quotes 275-300 ksi for fine wire: https://www.leespring.com/music-wire-versus-stainless-steel (fetched and confirmed; also confirms 302/304 usable to about 288-316 C and music wire to about 121 C and rusting). Bail leg is a cantilever of free length L = 35 mm (25 mm for a stiff variant), E = 190 GPa. The sustained bending allowable is taken as 600-1,100 MPa (about 0.4-0.7 of UTS, no set, no stress relaxation at 70 C). F_leg = sigma x (pi d^3/32)/L. RESULTS at 800 MPa: d=3.0, L=35 gives 61 N per leg, 121 N for two legs. d=2.5 gives 70 N for two legs. d=2.0 gives 36 N. d=3.0, L=25 gives 170 N (spring rate 290 N/mm). At 600-1,100 MPa, d=3/L=35 spans 91-167 N. SPRING RATE: k = 3EI/L^3 = 53 N/mm per leg (106 N/mm for two) for d=3, L=35, and deflection at the limit is 1.15 mm, comfortably larger than the 0.2-0.75 mm gasket stroke. GASKET STIFFNESS from Texin 985 (4.31-2.07 MPa between 10 and 20 % squeeze, 1.2 x 2.4 mm rib): 11.2 N/mm per mm of rib, which is 336 N/mm per latch at 30 mm pitch and 1,120 N/mm at 100 mm pitch. So the wire is 3-10x softer than the gasket. PRELOAD LOSS from set = 0.52 x ks/(kg+ks) = 11 % (30 mm pitch) to 4 % (100 mm pitch). PRINTED PART CHECK: wire in a 3 mm hole through a 6 mm wall carries 60 N at 3.3 MPa bearing, well below the 8-10 MPa working rule. PEAK: wire yield at about 1,100-1,300 MPa is roughly 230 N (3 mm wire), and printed holder/catch bearing at about 20 MPa short term over 18 mm2 is about 360 N. The hook root of the catch breaks first, so peak is taken as 250 N. WHAT IT MEANS FOR THE GASKET: line load = latch force / pitch. 60 N at 30 mm pitch is 2 N/mm and 120 N at 30 mm pitch is 4 N/mm. For the 700 mm reference path, 1.4-2.8 kN would need about 12-47 bail latches, which is not practical. Useful only for small boxes or light 1.2 mm ribs at 30-40 mm pitch. Hand force to close at 60 N is about 60/3 = 20 N plus the over-center snap.", "operating_force_N": 20, "preload_retention": "Best of the four. Steel spring wire stores the preload with negligible creep at 60-70 C. Gasket set costs an estimated 4-11 % of force (see formula) versus 30-58 % for a rigid fixed-stroke latch. The only plastic in the load path is the wire holders and catch at about 3 MPa, so holder creep adds little. Cold stiffening of the gasket (1.5-2x at -20 C) is damped by the wire spring and stays within the wire limit as long as the wire is sized so that 2x the 23 C force is still below 170 N.", "adjustable_preload": false, "positive_compression_stop": false, "scores": { "seal_suitability": 3, "outdoor_durability": 8, "printability": 7, "usability": 8 }, "best_materials": "Printed holders and catch in ASA (default). UV-stabilised PC raises holder margin if the bail is stiff (about 1.3-1.5x, own judgement). Wire: 304 or 316 spring-temper stainless. Do not use music wire outdoors since it rusts. Avoid PETG for the catch at 60-70 C (HDT 68-75 C).", "hardware": "1 bail of 2.5-3 mm 304/316 spring-temper stainless wire per latch (bent in a jig, 2-3 bends), optional stainless wire clip or cotter, optional M3 stainless screw retaining the wire end. A wire-bending jig is needed.", "design_guidelines": [ "Use 3 mm wire for sealing duty and 2-2.5 mm only for light-duty panel clips. Keep the free leg length 25-35 mm. A shorter leg raises force and stiffness together, so 25 mm gives about 170 N at 290 N/mm and the tolerance window is lost.", "Choose the wire leg length so the working deflection is 1-1.5 mm for a 0.4-0.5 mm gasket stroke. That puts the operating point in the soft part of the wire's range and keeps tolerance (+/-0.2 mm FDM) from swinging the force more than about 30 %.", "Print wire holders and catch lying flat (pin axis along Z). Wire hole 0.2-0.3 mm over wire diameter, at least 6 mm wall around the wire, 4+ perimeters, 0.2 mm layers, 100 % infill locally. Put a 1.5-2 mm fillet at the catch hook root.", "Add a separate printed hard stop beside each latch at about 0.75-0.8 x free bead height. The bail alone has no travel limit. Pitch of 30-50 mm for a flat 3 mm lid edge (rim bending limit about 28 mm), up to 110 mm only if the lid has a 20 mm skirt.", "Give the cam seat a detent notch or lock bump so vibration cannot walk the bail open. A bail that has not gone over center fully is the commonest failure.", "Use stainless (A2/A4 or 304/316) for everything metal. Do not mix with zinc-plated parts that are only good for 12-120 h salt spray (https://www.albanycountyfasteners.com/media/48/29/31/1764608481/fastener-materials-and-coatings-guide.pdf, cited from the brief; the PDF was not readable when fetched).", "Drain and seal wire holes against water ingress if they go through the wall. Prefer holders on the outside of the sealed boundary.", "Test the actual bail with a force gauge at the catch: spec 40-80 N at 1 mm deflection, repeat after 1 week at 60 C." ], "failure_modes": [ "Not enough force: 25-120 N per latch is below the 233-467 N per latch the reference lid needs with 6 latches, so the seal leaks or the lid bows between latches.", "Catch hook root cracks or creeps open at 60-70 C because the catch carries all clamp load in a small printed section, with a layer-line weak plane if printed standing.", "Wire takes a permanent set if overstretched (sustained above about 900-1,100 MPa) or if over-center is forced with a tool.", "Bail walks open under vibration or thermal movement if there is no detent.", "Cold: ASA is brittle near -30 C (3 kJ/m2 notched Charpy), so sharp internal corners at holders and catch can crack on a cold snap.", "Wire bearing hole wears or cuts into the print over thousands of cycles; stainless on plastic abrasion is slow but real." ], "existing_designs": [ { "title": "Steel-wire panel latch (Printables 1395495, 3dgo mirror)", "url": "https://3dgo.app/models/printables/1395495", "note": "1.6 mm wire; tension bar 2 mm PLA / 2.5 mm ASA per brief. Page returned HTTP 403 to my fetch so I could not confirm; light panel clip class (about 5-20 N)." }, { "title": "Sturdy print-in-place panel latch (Printables 1042802)", "url": "https://printables.com/model/1042802-sturdy-print-in-place-panel-latch-for-2020-extrusi", "note": "Lead only, from the brief; not a bail and not verified (403 from this environment)." } ], "sources": [ { "title": "Music wire versus stainless steel (Lee Spring)", "url": "https://www.leespring.com/music-wire-versus-stainless-steel", "note": "Fetched and verified: 275-300 ksi for 302/304 vs >400 ksi for music wire; music wire above 121 C weakens and rusts; stainless to about 288-316 C." }, { "title": "Texin 985 datasheet (D575 compressive stress curve)", "url": "https://sushengpolymer.com/media/pdf/phFiH7_Texin-985.pdf", "note": "From the brief, used for gasket stiffness (own calculation). Not re-fetched." }, { "title": "CNC Kitchen: ASA/PETG/PLA hook tests", "url": "https://www.cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament", "note": "Fetched and verified: ASA lying 57 kg vs standing 17 kg, PETG 55 vs 25 kg; ASA softens at 110 C, fails 120 C." }, { "title": "Steel-wire panel latch (Printables 1395495 via 3dgo)", "url": "https://3dgo.app/models/printables/1395495", "note": "Not verified (403)." } ], "review": { "id": "bail-wire-latch", "verdict": "corrected", "peak_clamp_force_N": 200, "sustained_clamp_force_N": { "low": 20, "typical": 50, "high": 90 }, "scores": { "seal_suitability": 3, "outdoor_durability": 7, "printability": 7, "usability": 7 }, "issues": [ "Peak is internally inconsistent: with the analyst's own formula F = 2*sigma*Z/L (3 mm wire, Z = 2.65 mm3, L = 35 mm), 1,100-1,300 MPa gives 167-197 N for both legs, not ~230 N (that needs ~1,500 MPa, i.e. near UTS). Peak lowered to 200 N.", "'Printed parts see only ~3 MPa' contradicts the analyst's own cam-hook analysis. A catch hook of 12x7 mm with a 2.25 mm throat gives 0.115 MPa/N (Winkler), so 60 N is ~7 MPa and 120 N is ~14 MPa, against the 3-5 MPa cautious in-plane limit. A 16x8 mm hook gives 0.075 MPa/N, i.e. 4.5 MPa at 60 N and 9 MPa at 120 N. 120 N is reachable only with a bulky post-type catch of about 12x10 mm section, which is hard to fit in the 70x35x30 envelope. High lowered to 90 N, typical to 50 N.", "The wire-flex force is the peak at the over-centre toggle. The holding force at the locked position is lower than stiffness x deflection, and no source or calculation covers that drop. The 60 N 'sustained' figure therefore carries an unquantified downside.", "Stroke tolerance: two 3 mm legs at 106 N/mm times FDM tolerance of +/-0.2 mm gives +/-21 N, which is +/-40 % of a 50 N latch. There is no adjustment or hard stop, so latch-to-latch spread is large. Some latches will leave a gap and others will not reach over-centre.", "Wire strength inputs are assumptions. The 1,500-1,700 MPa UTS for 3 mm 304 spring temper is unsourced. Lee Spring quotes 275-300 ksi for 302/304 without tying it to a diameter. A cold-bent bail without stress relief has a lower elastic limit at the bends. The 800 MPa sustained stress is a reasonable no-set design stress, and stainless wire relaxation at 70 C is negligible, which is the real strength of this design.", "Target force cannot be met: at ~50 N and a 25-30 mm pitch (rim-bending limit) the line load is 1.7-2 N/mm. The 700 mm reference path would need ~28-56 latches. Only suitable for small boxes (perimeter below ~300 mm) with a light 1.2 mm rib.", "Both existing-design links (3dgo/Printables 1395495, Printables 1042802) return 403, so no printed bail has measured data. force_basis stays 'estimated', and the 'best of four' preload-retention claim rests only on the formula loss = set x ks/(kg+ks). I recomputed that as 12 % at 30 mm pitch and 4.5 % at 100 mm pitch.", "Gasket stiffness uses the Texin curve with no shape-factor or printed-fill correction. With the stated +/-2x uncertainty, 'wire is 3-10x softer than the gasket' really means 1.5-10x." ], "confidence": "medium", "reviewer_notes": "Independent recomputation. Wire: Z = pi d^3/32 = 2.651 mm3, I = 3.976 mm4, k = 3EI/L^3 = 52.9 N/mm per leg at L = 35 mm (checks). F = sigma Z/L: 61 N per leg at 800 MPa (checks), 45 N at 600 MPa, 83-98 N at 1,100-1,300 MPa per leg, so ~167-197 N for the pair at yield. L = 25 mm gives 170 N at 800 MPa and 290 N/mm (checks). Gasket stiffness from the Texin 10-20 % stress difference (2.24 MPa) over 0.24 mm stroke x 1.2 mm width = 11.2 N/mm per mm of rib, which is 336 N/mm at 30 mm pitch (checks). Set loss: 0.52 x 106/(336+106) = 12.5 % (analyst 11 %). Printed-side check with a Winkler curved-beam model (not the 1.3 factor) shows the catch is the limit, so I trimmed sustained and peak. Steel is not the limit; the printed catch is. Sources: the Lee Spring page is confirmed (302/304 275-300 ksi, music wire >400 ksi and rusts, music wire weakens above 121 C, stainless good to 288-316 C). CNC Kitchen hook test is confirmed (ASA lying 57 kg vs standing 17 kg = 30 %). I decoded the Texin 985 PDF locally: D575 values 0.345/1.03/2.07/3.10/4.31/5.52/16.5 MPa, flexural modulus 26.9 vs 59.0 MPa, compression set 16/19 % (23 C) and 40/80 % (70 C) are all confirmed. WebSearch budget was exhausted, so I could not look for independent wire-bail force data; all model pages return 403. Scores: usability trimmed 8 to 7 (tolerance-sensitive snap, 25+ latches); durability trimmed 8 to 7 (catch hook creep or cold cracking at 60-70 C / -30 C and wire-hole wear are untested); seal 3 stands.", "dead_or_misquoted_sources": [ "https://3dgo.app/models/printables/1395495 - HTTP 403 to me too; unverifiable (analyst correctly flagged it).", "https://printables.com/model/1042802-sturdy-print-in-place-panel-latch-for-2020-extrusi - HTTP 403; unverifiable, and it is a panel latch, not a bail.", "https://www.albanycountyfasteners.com/media/48/29/31/1764608481/fastener-materials-and-coatings-guide.pdf - not machine-readable to my fetch, so the 12-72 h / 96-120 h salt-spray figures are not re-checked (the analyst said the same).", "https://www.leespring.com/music-wire-versus-stainless-steel - confirmed, but the 275-300 ksi figure is a generic 302/304 range, not a diameter-specific one; 'fine wire' is the analyst's inference." ] } }, { "id": "cam-lever-steel-stud", "name": "Eccentric cam clamping lever on a steel stud with steel contact plate", "working_principle": "A printed lever with an eccentric cam pivots on a steel pin that passes through the eye of a steel stud. Swinging the lever 90-180 degrees makes the cam bear on a hardened washer or contact plate on the lid. The stud is pulled by the cam throw and clamps the lid. A fine-thread setting nut sets the preload and the cam end position. The clamp stays on after release because the cam reaches an over-center or friction-locked position.", "mechanical_advantage": "About 19-21:1, taken from the manufacturer force table for steel GN 927.2: 75 N gives 1,450 N (19.3:1, 33 mm arm), 125 N gives 2,600 N (20.8:1, 47 mm), 200 N gives 4,300 N (21.5:1, 62 mm), 350 N gives 7,000 N (20.0:1, 76 mm). Printed version with a 50 mm lever and 2.5 mm effective cam offset (friction included) gives about 20:1. A cam throw of e = 2 mm gives about 3-4 mm of stud travel over 180 degrees, far more than the 0.2-0.75 mm the gasket needs, so a series spring fits in the stroke.", "peak_clamp_force_N": 1400, "sustained_clamp_force_N": { "low": 300, "typical": 450, "high": 700 }, "limiting_factor": "Bearing of the steel pivot pin in the printed lever ears (4-5 mm pin, 2 x 6-8 mm ears, about 8-10 MPa sustained). Next: the printed cam face (flat-spots unless a steel plate or insert is used) and the stud anchor in the base (insert pull-out or Z-direction load across layers). Steel stud and pin are never the limit: class 8.8 M5 proof load is 8.2 kN.", "force_basis": "calculated", "calculation": "NO PRINTED CAM-LEVER TEST EXISTS in anything I could reach; the web-search tool refused new searches (budget exhausted). The steel path is verified from the manufacturer table; the printed limits are my own calculation. STEEL REFERENCE (fetched and confirmed by me): GN 927.2 table 75/125/200/350 N hand force gives 1,450/2,600/4,300/7,000 N; recommended safety factors 1.2-1.5 static, 1.8-2.4 pulsating, 3-4 alternating; friction coefficients plastic/steel 0.15, plastic/plastic 0.25, steel/steel 0.2 (https://elesa.com/en/elesab2bstoreca/Clamping-handles--Cam-levers--GN9272-A--d1). GN 927.7 family reaches 8 kN and type A has an adjustable contact plate set by a fine-thread knurled nut (https://ctemag.com/?p=107957, fetched and confirmed). PRINTED PIVOT BEARING (own calc, ASA, working rule 8-10 MPa): M4 pin, 2 ears x 6 mm: 4 x 12 = 48 mm2 gives 384-480 N. M5 pin, 2 x 8 mm: 5 x 16 = 80 mm2 gives 640-800 N. EAR NET SECTION (14 mm boss, 5 mm hole, 2 x 8 mm ears, in-plane XY load): 144 mm2, so 4.9 MPa at 700 N, at the 3-5 MPa cautious limit. CAM FACE: Hertz line contact between printed cam (R = 9 mm, 12 mm wide, E* about 2 GPa) and a flat steel plate gives 42 / 54 / 64 MPa peak at 300 / 500 / 700 N. That is far above the 8-10 MPa sustained limit, so a bare printed cam will flat-spot and creep. Use a steel contact plate and a steel cam insert or dowel. ANCHOR: stud threads into an M5 heat-set insert in a thick base ledge. Insert pull-out is 119 kg (about 1.17 kN) for M3 in PETG at room temperature, short term, in flat 4-perimeter 100 % infill coupons (https://www.cnckitchen.com/blog/helicoils-threaded-insets-and-embedded-nuts-in-3d-prints-strength-amp-strength-assessment, fetched and confirmed). Derate to about 0.3-0.4 for sustained load at 60-70 C: an M5 insert in a 6+ mm ledge supports about 400-700 N. If the ledge load crosses layers (box printed upright, stud pulling along Z), allow only about 2 MPa across layers. COMBINED SUSTAINED RANGE: 300 / 450 / 700 N (low = M4 pin, typical = M5 pin with 2 x 7 mm ears, high = M5 pin, 2 x 8 mm ears, steel plate). PEAK about 2-3x sustained, and the short-term pin bearing (about 30 MPa x 80 mm2 = 2.4 kN) is not the limit; ear tension and the anchor are, so take 1.4 kN (range 0.9-1.8 kN). HAND FORCE = clamp / 20: 450 N needs about 22-25 N at a 50 mm lever. SERIES SPRING: gasket stiffness from Texin 985 is 11.2 N/mm per mm of rib, which is 1,120 N/mm at 100 mm pitch. A spring or Belleville stack with ks = kg/4 = 280 N/mm deflects 1.6 mm at 450 N and cuts set loss to 0.52 x 280/(1,120+280) = 10 %, versus 30-58 % for the rigid stud. COLD: a rigid 300 N preload at 23 C becomes 450-600 N at -20 C (Texin modulus 2.2x at -30 C), which is the sustained ceiling, so the series spring is also the cold protection. LATCH COUNT: 4 latches x 450 N = 1.8 kN covers the 1.4 kN low end; 6 latches x 450 N = 2.7 kN covers about the 2.8 kN high end, marginal with the +20-30 % corner load.", "operating_force_N": 23, "preload_retention": "Rigid as drawn: a steel stud of fixed length loses 30-58 % of force to 85A compression set after hot sun (52 % set for printed Ultrafuse at 70 C) plus a few percent from ear creep. A series spring (Belleville stack or stainless spring on the stud under the setting nut, ks about gasket/4) brings the loss to about 10 %. The setting nut re-adjusts preload in seconds, so the best practice is to check after the first hot week and each season.", "adjustable_preload": true, "positive_compression_stop": true, "scores": { "seal_suitability": 8, "outdoor_durability": 7, "printability": 6, "usability": 8 }, "best_materials": "ASA lever and base (default). UV-stabilised PC raises pin-bearing and heat creep margin about 1.3-1.5x (own judgement, unmeasured). PETG and PETG-CF are marginal at 60-70 C (HDT 68 C) and should be avoided for the lever. PA-CF mainly adds stiffness but takes up water (PA6-CF 3.33 % water) and creeps, so avoid PA6-CF outdoors.", "hardware": "1x M4-M6 A2/A4 stainless stud (eye or cross-drilled) and fine-thread (M5x0.5 or M6x0.75) setting nut, 1x 4-5 mm A4 stainless pivot pin with retaining clip, hardened stainless washer or 1.5-2 mm steel plate as cam contact, optional steel dowel as cam insert, 2-4 stainless Belleville washers or a stainless spring, an M5 heat-set insert (brass) or stainless captive nut for the anchor, optional spring-ball detent.", "design_guidelines": [ "Print the lever flat, pin axis along Z, so the cam, ears and arm lie in the XY plane. Use 4+ perimeters and 0.2 mm layers or finer, with 100 % infill in the cam body.", "Ears: 2 x 7-8 mm thick, 14+ mm boss width around a 5 mm pin, at least 4.5 mm edge distance. Use a ground stainless pin with a 0.1-0.15 mm clearance fit and a retaining E-clip or push-nut. M4 pin with 2 x 6 mm ears gives only 380-480 N.", "Put a hardened washer or 1.5-2 mm steel plate under the cam, and make the cam radius at least 9 mm and 12 mm wide. A bare printed cam sees ~50 MPa Hertz stress and will flat-spot. Round the cam edges to 1 mm radius so the steel plate is not edge-loaded.", "Add a series spring (2-4 Belleville washers or a stainless spring) with a rate about a quarter of the gasket stiffness per latch (about 250-300 N/mm at 100 mm pitch, 1.5 mm deflection at 450 N). Tune cam throw e = 1.5-2 mm so at least 2 mm of stroke exists.", "Add a printed hard stop beside each latch at about 0.75-0.8 x free bead height (brief), and a lever end-stop so the cam cannot go past its over-center point. Provide a detent or spring ball to keep the lever closed under vibration.", "Anchor the stud in a thick (6+ mm) horizontal ledge with a heat-set insert whose axis is parallel to the load, or hook the anchor so the pull is carried in compression. If the box is printed upright, the load crosses layers: allow only about 30 % (29 % per CNC Kitchen hook tests), and use a separate lying-printed bracket screwed to the box wall.", "Set the setting nut so that the lever just reaches its stop at the target squeeze of 15-22 % and not at maximum. Mark the nut position. Re-check after the first hot week.", "Pitch limit: with a flat 3 mm lid edge latch pitch is limited to about 28 mm by rim bending (own calc), about 110 mm with a 20 mm skirt. Stiffen the rim before adding latch strength.", "Use A2/A4 stainless or yellow-zinc or better. Plain zinc is only 12-72 h salt-spray, per the brief." ], "failure_modes": [ "Printed cam flat-spots or creeps under the steel plate edge, losing preload, and lets the lever back off.", "Pivot-pin bearing creep in the ears at 60-70 C: ears elongate, lever slumps, preload drops. Ear tension cracks along layer lines if the ears are printed standing.", "Fixed-length stud loses 30-58 % of its force after hot sun due to TPU compression set, and rises by 1.5-2x in the cold, so a latch set at 450 N in summer exceeds the ear limit in winter if it has no series spring.", "Anchor insert pulls out of a thin ledge (hot, long-term) or the wall shears across layers.", "Over-center lever opens in vibration if there is no detent.", "ASA ears crack at sharp corners near -30 C (3 kJ/m2 notched Charpy)." ], "existing_designs": [ { "title": "Elesa GN 927.2 cam levers (steel, manufacturer table)", "url": "https://elesa.com/en/elesab2bstoreca/Clamping-handles--Cam-levers--GN9272-A--d1", "note": "Verified: force table, safety factors, friction coefficients. Steel product, not printed." }, { "title": "GN 927.7 clamping levers (CTE Magazine)", "url": "https://ctemag.com/?p=107957", "note": "Verified: up to 8 kN, type A adjustable contact plate via fine-thread nut. Steel." }, { "title": "ELESA metal cam clamp datasheet (RS)", "url": "https://docs.rs-online.com/df90/A700000013422799.pdf", "note": "LAC.44 3,500 N per brief. Not re-fetched." }, { "title": "No printed cam-lever on a steel stud found", "url": "https://www.printables.com/model/355435-cam-latch-for-boxes", "note": "Closest printed relative is a hook cam latch; its page returned HTTP 403 to my fetch. See cam-hook-printed." } ], "sources": [ { "title": "Elesa GN 927.2 cam levers", "url": "https://elesa.com/en/elesab2bstoreca/Clamping-handles--Cam-levers--GN9272-A--d1", "note": "Fetched and confirmed: 75/125/200/350 N hand force gives 1,450/2,600/4,300/7,000 N; safety factors; friction coefficients." }, { "title": "GN 927.7 clamping levers (CTE Magazine)", "url": "https://ctemag.com/?p=107957", "note": "Fetched and confirmed: up to 8 kN; adjustable contact plate." }, { "title": "ISO metric thread proof loads (Optimas)", "url": "https://international.optimas.com/technical-resources/iso-metric-thread-proof-loads", "note": "Fetched and confirmed: class 8.8 proof loads M3 2.92, M4 5.10, M5 8.23, M6 11.6 kN. No A2-70 values on the page." }, { "title": "CNC Kitchen: threaded inserts and embedded nuts in 3D prints", "url": "https://www.cnckitchen.com/blog/helicoils-threaded-insets-and-embedded-nuts-in-3d-prints-strength-amp-strength-assessment", "note": "Fetched and confirmed: M3 in PETG: direct screw 118 kg, heat-set insert 119 kg, side-pocket nut 86 kg, bottom-pocket nut about 166 kg; room temperature, short term." }, { "title": "CNC Kitchen: ASA/PETG/PLA hook tests", "url": "https://www.cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament", "note": "Fetched and confirmed: ASA lying 57 kg vs standing 17 kg (29 %)." }, { "title": "Texin 985 datasheet", "url": "https://sushengpolymer.com/media/pdf/phFiH7_Texin-985.pdf", "note": "From the brief; gasket stiffness and cold modulus. Not re-fetched." } ], "review": { "id": "cam-lever-steel-stud", "verdict": "corrected", "peak_clamp_force_N": 1000, "sustained_clamp_force_N": { "low": 220, "typical": 350, "high": 550 }, "scores": { "seal_suitability": 7, "outdoor_durability": 7, "printability": 6, "usability": 8 }, "issues": [ "450 N typical sits on the upper edge of the printed-ear bearing rule: M5 pin, 2x7 mm ears = 70 mm2 gives 6.4 MPa nominal at 450 N. A clearance-fit pin concentrates that by ~1.3x. At the cautious 6 MPa the ceiling is 420 N, and the anchor and flange paths cut it further. Typical lowered to 350 N, high to 550 N.", "Unchecked load paths. Only insert pull-out was checked at the anchor. A base lug that carries 400 N at an 8 mm arm, 14 mm wide x 6 mm thick, sees ~38 MPa bending (about 10 MPa needs 12 mm thickness or a gusset). The lid-side contact plate on a 3-4 mm flange has the same problem unless the washer sits directly over the supported rim. These bending paths, not the steel and not the pin, probably set the real limit within the 70x35x30 envelope.", "The anchor derating is judgement stacked on an M3-in-PETG coupon. The CNC Kitchen article (119 kg heat-set insert, 118 kg direct screw, 86 kg side nut, 166 kg bottom nut) states 4 perimeters / 100 % infill flat coupons but gives no temperature or duration. The 'room temperature, short term' label is assumed. Scaling to M5 and the 0.3-0.4 hot-sustained factor are unmeasured (my estimate 300-500 N).", "Hand force: the Elesa 19-21:1 ratio is verified, but it is for steel levers (33-76 mm arm) at 75-350 N hand force. For a printed plastic-on-steel cam (R = 9 mm, mu = 0.15 at cam and pin, e = 2.5 mm, geometric torque max 0.65 F e) I get ~15:1, so about 27 N at the lever for 400 N, not 20 N. Still within the 20-50 N comfort band.", "Peak lowered from 1,400 to 1,000 N. Short-term pin bearing (30 MPa x 70 mm2 = 2.1 kN) and net ear tension are not the limit, but the anchor, lug and flange bending are, and the only polymer-lever precedent (Elesa LAC glass-fibre PA, 3.5-7 kN rated) is moulded PA-GF, roughly 4x stronger than printed ASA before anisotropy knock-downs.", "A rigid stud is not viable outdoors: 30-58 % force loss to 85A set at 70 C and 1.5-2x force rise at -20 C (flex modulus 26.9 to 59.0 MPa, verified). The series spring (Belleville stack) and a hard stop are mandatory, not optional. They add stainless hardware beyond 'printed latch': stud, pin, plate, insert, nut and springs. The printed share is the lever and bracket only.", "The printed cam face is not usable bare. My Hertz check (R = 9 mm, 12 mm wide, E* ~2 GPa) gives 42 / 52 / 64 MPa at 300 / 450 / 700 N. A steel plate plus steel cam dowel is required. This is the analyst's own conclusion, but it means the 'printed' mechanism really is a hybrid.", "No printed cam-lever-on-stud has any force or hot-soak test. The 8-10 MPa bearing and 2 MPa interlayer figures are the brief's judgement. Hot creep of the ears should be confirmed with a 1-week 65 C force-gauge soak before adopting." ], "confidence": "low", "reviewer_notes": "Independent recomputation. Steel: Elesa GN 927.2 table (hand 75/125/200/350 N gives clamp 1,450/2,600/4,300/7,000 N, ratios 19.3/20.8/21.5/20.0) is confirmed. Elesa says the lever arm is not stated and my fetch read it as inferred (33/47/62/76 mm), consistent with the analyst. Safety factors 1.2-1.5 static, 1.8-2.4 pulsating, 3-4 alternating, and friction (plastic/steel 0.15, plastic/plastic 0.25, steel/steel 0.2) are confirmed. GN 927.7 'up to 8 kN' with type A adjustable plate and fine-thread nut is confirmed (CTE Magazine). Optimas class 8.8 proof loads M3/M4/M5/M6 = 2.92/5.10/8.23/11.6 kN are confirmed; the page has no A2-70 values. Printed side: bearing M4 2x6 = 48 mm2 (288/384/480 N at 6/8/10 MPa), M5 2x7 = 70 mm2 (420/560/700 N), M5 2x8 = 80 mm2 (480/640/800 N). The analyst's bearing arithmetic is right; I disagree on what limits the system. Hertz numbers reproduce (54 MPa at 500 N). Series-spring set loss 0.52 x 280/(1,120+280) = 10 % (checks). Useful new source: the Elesa LAC datasheet that the analyst cites from the brief as 'metal' is in fact a GLASS-FIBRE REINFORCED POLYAMIDE lever body with a zinc or AISI 303 pin, ring-nut adjustable. Fmax is 3,500 N for LAC.44 (M5/M6), 4,000 N for LAC.63 and 7,000 N for LAC.80, with a 0.5 / 0.75 / 1.0 mm column x. That strongly supports the 'polymer lever + steel pin + adjustable nut' architecture and the sub-1 mm stroke, but it is a moulded PA-GF part with a rated maximum, not a sustained printed ASA rating. Net: architecture is the best of the four for force and adjustability, but 450 N sustained is optimistic by ~20 % and the lug/flange paths are unchecked, so I report 350 N. WebSearch budget was exhausted; no independent printed cam-lever data could be sought.", "dead_or_misquoted_sources": [ "https://docs.rs-online.com/df90/A700000013422799.pdf - MISDESCRIBED as 'ELESA metal cam clamp'. It is the Elesa LAC technopolymer (glass-fibre PA) cam clamp with a steel or 303 stainless pin. LAC.44 Fmax 3,500 N is confirmed from the table, but it is a moulded polymer part's rated maximum.", "https://www.cnckitchen.com/blog/helicoils-threaded-insets-and-embedded-nuts-in-3d-prints-strength-amp-strength-assessment - numbers confirmed (118/119/86/166 kg, M3 PETG, 4 perimeters, 100 % infill), but the article does not state temperature or test duration, so 'room temperature, short term' is an assumption.", "https://www.printables.com/model/355435-cam-latch-for-boxes - HTTP 403 to me too; cited only as a hook-style relative.", "https://elesa.com/en/elesab2bstoreca/Clamping-handles--Cam-levers--GN9272-A--d1 - confirmed, but it states no cam stroke and no explicit lever length; the 33/47/62/76 mm arms are inferred from the calculation example." ] } }, { "id": "cam-hook-printed", "name": "Printed cam-lever hook latch (zx82net / cam-latch-for-boxes style)", "working_principle": "Two printed parts. A lever with an eccentric cam end pivots on a base pin (M3/M4 screw or steel pin). A hook on the lever engages a catch bar on the lid, and swinging the lever over center pulls the lid down by the cam throw. The final position is a fixed geometric stroke, so force is stroke-controlled: it depends on how stiff the printed chain and the gasket are.", "mechanical_advantage": "About 8-12:1 (50 mm lever, 4-6 mm effective cam offset including friction). Hand force to close at 80 N clamp is about 8-12 N plus the over-center snap. The ratio is not the limit: the hook section is.", "peak_clamp_force_N": 450, "sustained_clamp_force_N": { "low": 40, "typical": 80, "high": 140 }, "limiting_factor": "Bending plus tension in the printed hook jaw (curved-beam root) at the long-term in-plane stress for ASA at 60-70 C of about 3-8 MPa. After that, creep of hook and cam, and fixed-stroke tolerance (+/-0.2 mm FDM vs. 0.2-0.75 mm gasket window). Pivot pins are not the limit.", "force_basis": "estimated", "calculation": "NO PUBLISHED FORCE TEST for this printed latch type; the web-search tool refused new searches (budget exhausted) and the model pages (Printables, Thingiverse, MyMiniFactory, MakerWorld) returned HTTP 403, so the leak-test and creep-warning statements below are from the brief and are not re-checked. HOOK ROOT (own calc, curved-beam factor 1.3, throat 4.5 mm, load offset from section centroid e = r_in + t/2): sigma/F = 1.3 x (e/Z + 1/A). Jaw b x t = 10x5 mm gives 0.174 MPa per N: 29 N at 5 MPa. b x t = 12x7 mm gives 0.092: 33 N at 3 MPa, 54 N at 5 MPa, 87 N at 8 MPa. b x t = 16x8 mm gives 0.058: 52 N at 3 MPa, 87 N at 5 MPa, 138 N at 8 MPa. The stress levels are the working rule from the brief (3-5 MPa cautious, up to 5-8 MPa optimistic, in-plane ASA at 60-70 C). A typical maker-sized hook (8x5 mm) is 20-40 N. Envelope-filling hook (16x8 mm) gives 40 / 85 / 140 N. SUSTAINED taken as 40 / 80 / 140 N, which matches the 60-150 N maker range in the brief. PIVOT: M4 pin, 2 x 6 mm ears: 48 mm2 x 8-10 MPa = 380-480 N, so not limiting. PEAK: short-term in-plane ASA tension of about 35 MPa over the 16x8 hook gives about 600 N; with stress concentrations and layer faults take 450 N (range 250-600 N). Proxy: CNC Kitchen's printed hook test failed ASA printed lying at 57 kg (about 559 N) and standing at 17 kg (about 167 N) and PETG 55 vs 25 kg (geometry not the same as this hook; https://www.cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament, fetched and confirmed). PRELOAD RETENTION (own estimate): the chain is rigid, so gasket set (30-58 % at 70 C) is not compensated, plus hook creep. A hook arm 40 mm long at 5 MPa and E about 1.3 GPa at 60 C strains about 0.4 % elastic, and creep may double it: 0.16 mm of lost stroke, similar to the 0.2-0.75 mm gasket window. Expect to keep only 30-60 % of the force after a hot season. COLD: a rigid latch at 80 N at 23 C may see 120-160 N at -20 C (Texin modulus 2.2x), and ASA is brittle (3 kJ/m2 Charpy at -30 C), so set the 23 C preload at 50-60 N. GASKET LINE LOAD: 80 N at 50 mm pitch is 1.6 N/mm, which is just under the 1.7 N/mm needed for Garlock's 1.4 MPa seal stress on a 1.2 mm rib. To get 2.8 kN on the reference lid would need about 20-35 latches. Hand force at 80 N is about 8-12 N.", "operating_force_N": 12, "preload_retention": "Poor. Fixed stroke, no spring and no adjustment, so gasket compression set (30-58 % loss at 70 C) and hook/cam creep (PETG and PLA creep more; designer warns PLA loosens the seal) both go straight into lost force. Expect 30-60 % of the original force left after a hot season. Cold has the opposite effect: force rises 1.5-2x at -20 C.", "adjustable_preload": false, "positive_compression_stop": true, "scores": { "seal_suitability": 3, "outdoor_durability": 5, "printability": 9, "usability": 8 }, "best_materials": "ASA (default), 100 % infill on the lever and hook. UV-stabilised PC probably raises the sustained limit by 1.3-1.5x (own judgement). PETG is marginal at 60-70 C. PLA is unsuitable (creeps, fails near 60-65 C). PETG-CF has HDT 68 C, so the carbon fibre does not help heat.", "hardware": "M3 or M4 stainless screws and nuts or heat-set inserts as pivots (optionally a 4 mm stainless pin), optional M3 stainless set screw as adjustable catch, TPU 85A gasket. Optional stainless torsion or leaf spring to give a small spring preload.", "design_guidelines": [ "Print the lever and hook lying flat so layers run in the plane of the hook, pin axis along Z. Use 100 % infill, 4+ perimeters and 0.2 mm layers or finer for the lever and the catch.", "Make the hook jaw at least 12x7 mm (16x8 mm if the envelope allows). Throat radius 2.5 mm min. Use 2 mm fillets at the hook root and avoid sharp inside corners, since ASA is notch-sensitive in the cold.", "Use steel pins or M4 screws through bushed holes. Pivots are not the limit at 80 N, but a steel pin avoids wear.", "Keep the 23 C preload at 50-60 N or less so the cold peak (1.5-2x) stays within the hook limit. Do not rely on the lever force to compress the gasket: fit a printed hard stop beside the latch at about 0.75-0.8 x free bead height.", "Add an adjustable catch (M3 or M4 set screw or eccentric) if you need to compensate for +/-0.2 mm FDM tolerance and compression set. Without it, expect large latch-to-latch variation.", "Add a detent bump on the cam so it cannot back off. Use a thin TPU or steel spring clip for outdoor vibration.", "Latch pitch 30-50 mm for a flat 3 mm lid edge (rim limit about 28 mm), because 80 N at 50 mm is only 1.6 N/mm. Stiffen the rim with a skirt before adding more latches.", "Use small boxes (perimeter below about 400 mm) and a light gasket (1.2 mm rib, 1.7-2 N/mm), or combine with an adjustable stud design for larger lids." ], "failure_modes": [ "Hook jaw creeps open or cracks along layer lines at 60-70 C because it carries bending plus tension at 3-8 MPa.", "Cam surface creeps or flat-spots so the lever backs off and the seal loosens.", "Fixed stroke: tolerance spread of +/-0.2 mm swings the force from near zero to the limit. Some latches leak, others overload.", "Cold overload: force rises 1.5-2x at -20 C and ASA is brittle near -30 C, so the hook root cracks.", "Not enough total force: 40-140 N per latch is well under the 233-467 N per latch needed on the reference lid.", "Over-center lever springs open in vibration if there is no detent." ], "existing_designs": [ { "title": "zx82net Customizable Rugged Waterproof Box (MyMiniFactory)", "url": "https://www.myminifactory.com/object/3d-print-zx82net-customizable-rugged-waterproof-box-146437", "note": "Cam latch, TPU or cord seal. Per brief: reviewer submerged it 10 cm for 10 min, dry with thick seal, about 10 ml in with thin seal. Page returned 403 to my fetch; not verified." }, { "title": "zx82net box (Thingiverse 3338826)", "url": "https://www.thingiverse.com/thing:3338826", "note": "Per brief: designer recommends PETG over PLA since PLA creeps. 403 to my fetch; not verified." }, { "title": "Cam latch for boxes (Printables 355435)", "url": "https://www.printables.com/model/355435-cam-latch-for-boxes", "note": "Per brief: M4 mounting, 100 % infill on the latch, locking arms break first. 403 to my fetch; not verified." }, { "title": "Cam latch for boxes, stronger remix (MakerWorld 87535)", "url": "https://makerworld.com/en/models/87535-cam-latch-for-boxes", "note": "Stronger-cam remix per brief; not verified." }, { "title": "Waterproof Box (MakerWorld 454290)", "url": "https://makerworld.com/en/models/454290-waterproof-box", "note": "Cam latch plus printed TPU or silicone seal, 8x M3x20, 3 perimeters >30 % infill, tested PLA/PETG only per brief. 403 to my fetch; not verified." } ], "sources": [ { "title": "CNC Kitchen: ASA/PETG/PLA hook tests and oven test", "url": "https://www.cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament", "note": "Fetched and confirmed: lying vs standing hook failure loads; PETG softens 80 C, ASA 110 C." }, { "title": "Creep resistance of 3D printed parts (FilamentSpecs)", "url": "https://filamentspecs.com/creep-resistance-3d-printed-parts/", "note": "Fetched and confirmed: bolted joint preload loss about 11.5 % PETG vs about 3 % PLA over 7 days (do not transfer to other sizes)." }, { "title": "zx82net box (MyMiniFactory)", "url": "https://www.myminifactory.com/object/3d-print-zx82net-customizable-rugged-waterproof-box-146437", "note": "From the brief. Not verified (403)." }, { "title": "zx82net box (Thingiverse 3338826)", "url": "https://www.thingiverse.com/thing:3338826", "note": "From the brief. Not verified (403)." }, { "title": "Texin 985 datasheet", "url": "https://sushengpolymer.com/media/pdf/phFiH7_Texin-985.pdf", "note": "From the brief. Gasket line load and cold modulus." } ], "review": { "id": "cam-hook-printed", "verdict": "corrected", "peak_clamp_force_N": 350, "sustained_clamp_force_N": { "low": 25, "typical": 55, "high": 100 }, "scores": { "seal_suitability": 3, "outdoor_durability": 4, "printability": 9, "usability": 8 }, "issues": [ "The curved-beam factor of 1.3 is too optimistic for a tight-throat hook. A Winkler solution (inner radius 2.25 mm, load through the centre of curvature, plus direct tension) gives 0.115 MPa/N for a 12x7 hook (analyst 0.092) and 0.075 MPa/N for 16x8 (analyst 0.058), i.e. 25-30 % higher stress. At 3/5/8 MPa the capacity is 26/44/70 N for 12x7 and 40/66/106 N for 16x8, so typical drops from 80 to ~55 N and high from 140 to ~100 N.", "Peak: 35 MPa ASA in-plane at the inner fibre gives 305 N (12x7) to 465 N (16x8). With layer faults and notch effects I use 350 N (range 200-550). The CNC Kitchen hook failing at 559 N is a different geometry, so it is only a loose proxy.", "Fixed-stroke force is unpredictable. The printed lever/hook chain has stiffness of the same order as the gasket (~100-400 N/mm vs 336 N/mm at 30 mm pitch), so +/-0.2 mm FDM tolerance is +/-20-80 N, i.e. +/-40-100 % of the 55 N typical. With no spring and no adjustment, some latches leak and others overload the hook. This is the main reason it ranks last on seal suitability.", "Preload retention: no steel in the load path, so gasket set (30-58 % at 70 C) and ASA creep at 4-8 MPa both come straight out of the force. The 'keeps 30-60 %' figure is a guess. Cold gives 1.5-2x (modulus 26.9 to 59.0 MPa, verified), and 55 N at 23 C may reach 80-110 N at -20 C next to a brittle ASA hook root.", "Requirement mismatch: 55 N at 30 mm pitch = 1.8 N/mm, but at 50 mm pitch it is only 1.1 N/mm, below the 1.7 N/mm needed for the 1.4 MPa Garlock threshold on a 1.2 mm rib. The 700 mm reference lid would need ~25-50 latches. Only useful on small boxes (perimeter below ~300 mm) with a light rib.", "None of the five printed-design pages (MyMiniFactory, Thingiverse, Printables 355435, MakerWorld 87535, MakerWorld 454290) could be opened. The 10 cm / 10 min dunk test and 'PETG not PLA' creep warning are therefore brief-only hearsay. The dunk test used a soft cord/TPU seal at low load, which does not show sealing at the 1.7-4 N/mm line load.", "Pivot and ear bearing (M4, 2x6 mm = 48 mm2, 288-480 N at 6-10 MPa) is correctly not the limit. The analyst's statement about the hook root and layer orientation (print lying flat, pin along Z) is right and matches the CNC Kitchen lying/standing ratio (ASA 57 vs 17 kg = 30 %, PETG 55 vs 25 kg = 45 %)." ], "confidence": "medium", "reviewer_notes": "Independent recomputation using exact Winkler curved-beam stress for a rectangular hook section (b x t, r_i = 2.25 mm; centroid radius r_c = r_i + t/2; neutral axis r_n = t / ln(r_o/r_i); sigma_i = F r_c (r_n - r_i) / (A e_c r_i) + F/A). Results in MPa/N: 10x5 = 0.199, 12x7 = 0.115, 16x8 = 0.075 (a larger inner radius of 3 mm barely changes it, 0.076). Analyst values of 0.174 / 0.092 / 0.058 are 15-30 % low. Using the same 3/5/8 MPa working rule: 12x7 gives 26/44/70 N and 16x8 gives 40/66/106 N. That is where my 25/55/100 comes from (envelope-filling hook at ~4-5 MPa). Pivot bearing is not limiting (checked 48 mm2 x 6-10 MPa). Texin and CNC Kitchen hook-test numbers confirmed. The CNC Kitchen oven test also confirmed (PLA starts to give at 60 C, PETG 80 C, ASA 110 C; failure ~5-10 C later). The filamentspecs page confirms 11.5 % (PETG) vs 3 % (PLA) preload loss over 7 days but gives no bolt size, torque or temperature and has no ASA data, so it should not be transferred. All printed-design links returned HTTP 403, so existing-design claims stay unverified. WebSearch budget was exhausted, so no extra hot-soak or cam-latch force data could be searched for. Outdoor durability trimmed 5 to 4 because there is no steel spring to absorb creep and set. Printability stays 9 and usability 8 (12 N, one motion).", "dead_or_misquoted_sources": [ "https://www.myminifactory.com/object/3d-print-zx82net-customizable-rugged-waterproof-box-146437 - HTTP 403 to me too; dunk-test numbers unverified.", "https://www.thingiverse.com/thing:3338826 - HTTP 403; PETG-over-PLA creep advice unverified.", "https://www.printables.com/model/355435-cam-latch-for-boxes - HTTP 403; M4 mounting / 100 % infill / 'locking arms break first' unverified.", "https://makerworld.com/en/models/87535-cam-latch-for-boxes - HTTP 403; 'stronger cam' claim unverified.", "https://makerworld.com/en/models/454290-waterproof-box - not re-tested; analyst reports 403.", "https://filamentspecs.com/creep-resistance-3d-printed-parts/ - numbers confirmed but the page gives no bolt size, torque or temperature and no ASA data; not transferable to a hook or cam." ] } }, { "id": "swing-bolt-wing-nut", "name": "Swing bolt / eye bolt with wing nut or knob in a printed clevis", "working_principle": "A stainless M4-M5 swing bolt pivots on a pin in a printed clevis on the base. It swings into a slot on the lid flange, and a wing nut or knob on a steel washer tightens it. The clamp force is the screw preload F = T/(K d), so it is torque-controlled, continuously adjustable and can be re-tensioned any time. That makes it the best direct answer to TPU compression set, as long as the printed clevis ears and the slot seat carry the load.", "mechanical_advantage": "Screw MA with friction: F = T/(K d). For K = 0.2, d = 5 mm and a 35 mm wing span the ratio is 35:1 (hand force at the wing tips to clamp force). The ideal thread ratio is about 140:1 (2 pi r/pitch for 17.5 mm and 0.8 mm), but friction takes it to 35:1. It is not a lever or over-center.", "peak_clamp_force_N": 1500, "sustained_clamp_force_N": { "low": 300, "typical": 500, "high": 800 }, "limiting_factor": "Bearing of the steel pin in the printed clevis ears (4-5 mm pin, 2 x 6-8 mm ears at about 8-10 MPa sustained) and the slot seat under the washer. Hand torque is NOT limited by the bolt: a firm hand on a wing nut easily gives 1.5-2 N m, i.e. 1.5-2 kN on M5, above the clevis peak. The anchor of the clevis to the box (load across layers if it is integral with an upright-printed box) can limit even earlier.", "force_basis": "calculated", "calculation": "No test of a printed swing-bolt closure exists; the web-search tool refused new searches (budget exhausted) and the MDPI pin-bearing paper returned HTTP 403, so the printed limits are my own calculation from the working rules in the brief. PRELOAD (own calc, F = T/(K d)): K = 0.2: M3 at 0.5 N m gives 833 N, M4 at 0.5 N m gives 625 N, M4 at 1 N m gives 1,250 N, M5 at 0.5 N m gives 500 N, M5 at 1 N m gives 1,000 N, M5 at 1.5 N m gives 1,500 N. For stainless-on-stainless dry threads K = 0.3 gives 33 % less (M5 at 0.5 N m = 333 N). Class 8.8 proof loads are M3 2.92, M4 5.10, M5 8.23, M6 11.6 kN (https://international.optimas.com/technical-resources/iso-metric-thread-proof-loads, fetched and confirmed; no A2-70 numbers there). The DIN 444 M5 swing bolt in the one catalog page I could read is class 4.6 zinc-plated steel with a 5 mm eye and no stated load rating (https://www.aspenfasteners.com/m5-0-8-x-35mm-din-444-type-b-metric-precision-swing-eye-bolts-steel, fetched and confirmed), so zinc 4.6 is not an outdoor part: use A2/A4 stainless. Steel is never the limit. CLEVIS EARS (own calc, ASA, in-plane load): M4 pin, 2 x 6 mm: 48 mm2 x 8-10 MPa = 380-480 N. M5 pin, 2 x 7 mm: 70 mm2 gives 560-700 N. M5 pin, 2 x 8 mm: 80 mm2 gives 640-800 N. Net tension in ears (14 mm boss, 5 mm hole, 2 x 8 mm): 4.9 MPa at 700 N. SLOT SEAT: load crosses layers (lid printed flat, compression Z) and washer area matters. DIN 125 M5 washer (10 mm OD) has about 50 mm2 and sees 12 MPa at 600 N, too high. A DIN 9021 (15 mm OD) washer or a printed boss with 130 mm2 gives about 4.6 MPa at 600 N. ANCHOR: if the clevis is integral with an upright-printed box, the lug root (2 ears x 7 mm x 12 mm = 168 mm2) is loaded across layers: 168 x 2 MPa = about 340 N, and in the CNC Kitchen hook tests standing ASA failed at 29 % of lying (https://www.cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament, fetched and confirmed). So for 300-800 N the clevis must be a separate bracket printed flat and anchored by screws or inserts, or hooked under a ledge. SUSTAINED 300 / 500 / 800 N (low = M4 pin 2 x 6 mm or integral clevis, typical = M5 pin 2 x 7 mm, high = M5 pin 2 x 8 mm with big washer). PEAK about 1.2-2 kN: short-term bearing at about 30 MPa over 70 mm2 is 2.1 kN, and the slot seat across layers at 15-20 MPa over 100 mm2 is 1.5-2 kN; take 1,500 N. HAND EFFORT: to clamp 400 N on M5 at K 0.2 needs T = 400 N mm, i.e. 11 N at each wing tip with a 35 mm span; 500 N needs about 14 N per wing. OVER-TIGHTENING: a printed stop near the latch protects the gasket from over-squeeze but not the clevis: stop contact only transfers extra preload through the clevis. So cap the torque with a small knob (20 mm or less, about 0.3-0.7 N m by hand, 300-700 N on M5) or a slip-clutch knob. GASKET SET: rigid bolt loses 30-58 % of force at 70 C; a Belleville stack with ks = kg/4 (280 N/mm at 100 mm pitch, 1.6 mm deflection at 450 N) cuts it to about 10 %, or re-torque. COLD: 300 N at 23 C could be 450-600 N at -20 C on a rigid bolt. LATCH COUNT: 4 x 500 N = 2.0 kN covers the 1.4 kN low end; 6 x 500 N = 3.0 kN covers about the 2.8 kN high end including +20-30 % at corners.", "operating_force_N": 14, "preload_retention": "Rigid as built: 30-58 % of force is lost to gasket compression set after hot sun, but the preload is fully recoverable by re-tightening the nut, which is the reason it scores well for sealing. With a Belleville stack or spring under the nut the loss is about 10 %. Wing nuts back off under vibration unless a nyloc nut, spring washer or thread locker is used. Printed ear creep (3-8 MPa at 60-70 C) is a smaller second loss.", "adjustable_preload": true, "positive_compression_stop": false, "scores": { "seal_suitability": 8, "outdoor_durability": 8, "printability": 7, "usability": 4 }, "best_materials": "ASA clevis and knob (default). UV-stabilised PC for the clevis gives about 1.3-1.5x on sustained bearing (own judgement, unmeasured). PETG is marginal at 60-70 C. Avoid PA6-CF outdoors (3.33 % water uptake, -22 % XY strength). Steel: A2/A4 stainless bolt, wing nut and washers, not zinc 4.6.", "hardware": "1x DIN 444 A2/A4 stainless swing bolt M4-M5 (eye bolt with pin) per latch, A2/A4 stainless wing nut or knob (DIN 315 style) with nyloc or spring, DIN 9021 stainless washer (15 mm OD for M5) at the slot seat, 4-5 mm stainless pivot pin with E-clip, optional Belleville stack, M3-M4 screws or inserts for the clevis bracket.", "design_guidelines": [ "Make the clevis a separate bracket printed lying flat, pin axis along Z, ears loaded in the XY plane, 4+ perimeters, 0.2 mm layers. Do not make it integral with an upright-printed box: the load then crosses layers (about 29 % strength).", "Ears: 2 x 7-8 mm thick, 14+ mm boss width, 5 mm pin, 4.5 mm edge distance min, 2 mm fillets. M4 pin with 2 x 6 mm ears gives only 380-480 N. Fit a stainless pin with a retaining clip, not a printed pin.", "Anchor the bracket so the pull is carried in compression (hook it under a ledge) or in screw tension into heat-set inserts in a thick (6+ mm) boss. Check M3 insert pull-out of 119 kg (about 1.17 kN) for PETG at room temperature, short term, and derate to 0.3-0.4 for hot, sustained load.", "Slot in the lid flange: 5.5-6 mm wide, entry chamfer, seat face flat. Use a DIN 9021 (15 mm) washer, 4-5 MPa max across layers, or a wider printed boss.", "Limit hand torque: knob 20 mm or less, or a printed slip-clutch. 0.5 N m on M5 at K 0.2 is 500 N, 1.5 N m would give 1.5 kN and break the clevis.", "Add a printed hard stop beside each latch at about 0.75-0.8 x free bead height to stop gasket over-squeeze, plus a Belleville stack under the nut with ks = kg/4 (about 250-300 N/mm at 100 mm pitch) to keep the force through compression set.", "Re-tighten after the first hot week and each season; mark the nut position with paint. Use nyloc or a spring washer against vibration, and thread-locker only for non-service nuts.", "Pitch limit about 28 mm for a flat 3 mm lid edge (rim bending), about 110 mm with a 20 mm skirt: stiffen the rim before buying a stronger latch. Use 4-6 swing bolts for the reference lid, 6-8 if the rim is soft." ], "failure_modes": [ "Clevis ears creep or elongate at 60-70 C: the pin sinks into the ear, the bolt slumps and preload drops. Ears crack along layer lines if printed standing.", "Integral clevis on an upright-printed box tears out across layers at about 340 N or less.", "Over-tightening by hand (1.5-2 N m gives 1.5-2 kN on M5) overloads ears or slot seat, which fail suddenly.", "Wing nut backs off in vibration, or the slot-seat washer sinks into the lid flange (creep in compression across layers).", "Cold: preload rises 1.5-2x at -20 C on a rigid bolt; ASA ears crack from sharp corners at -30 C.", "Zinc 4.6 DIN 444 bolts rust in months (12-72 h salt spray) and seize. Stainless-on-stainless threads can gall; use anti-seize." ], "existing_designs": [ { "title": "DIN 444 type B swing eye bolts (Aspen Fasteners)", "url": "https://www.aspenfasteners.com/m5-0-8-x-35mm-din-444-type-b-metric-precision-swing-eye-bolts-steel", "note": "Verified: M5 x 35, 5 mm eye, class 4.6 zinc-plated, no load rating on the page. Steel part, not printed." }, { "title": "MakerWorld Tough Case (PETG snap latches + 85A TPU gasket)", "url": "https://www.makerworld.com/en/models/2385298", "note": "From the brief, closest printed latch plus 85A gasket design; snap latches, not a swing bolt. Not verified (403 from this environment)." }, { "title": "No printed swing-bolt closure with a force test found", "url": "https://mdpi.com/2073-4360/15/7/1660", "note": "Only a pin-bearing coupon study per the brief (189 MPa ultimate bearing, 3.6 kN fracture at W/D 3, short term, ABS/PLA). Page returned 403 to my fetch; do not use for sustained design." } ], "sources": [ { "title": "ISO metric thread proof loads (Optimas)", "url": "https://international.optimas.com/technical-resources/iso-metric-thread-proof-loads", "note": "Fetched and confirmed: class 8.8 proof loads M3 2.92, M4 5.10, M5 8.23, M6 11.6 kN." }, { "title": "DIN 444 type B swing eye bolts (Aspen Fasteners)", "url": "https://www.aspenfasteners.com/m5-0-8-x-35mm-din-444-type-b-metric-precision-swing-eye-bolts-steel", "note": "Fetched and confirmed: dimensions, class 4.6 zinc, no load rating." }, { "title": "CNC Kitchen: threaded inserts and embedded nuts in 3D prints", "url": "https://www.cnckitchen.com/blog/helicoils-threaded-insets-and-embedded-nuts-in-3d-prints-strength-amp-strength-assessment", "note": "Fetched and confirmed: M3 in PETG pull-out values (118 / 119 / 86 / 166 kg)." }, { "title": "CNC Kitchen: ASA/PETG/PLA hook tests", "url": "https://www.cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament", "note": "Fetched and confirmed: ASA standing 17 kg vs lying 57 kg." }, { "title": "CNC Kitchen: carbon fibre nylon preload creep", "url": "https://www.cnckitchen.com/blog/carbon-fiber-nylon-in-3d-printing-pa6-vs-pa12-tested", "note": "Fetched and confirmed: M4 at 0.8 N m, PA6 needed re-tightening almost daily; PA12 once in about half a week, similar to PLA and ASA." }, { "title": "Creep resistance of 3D printed parts (FilamentSpecs)", "url": "https://filamentspecs.com/creep-resistance-3d-printed-parts/", "note": "Fetched and confirmed: bolted PETG joints lost about 11.5 % preload in 7 days vs about 3 % for PLA." }, { "title": "Pin-bearing strength of AM polymer parts (Polymers 2023)", "url": "https://mdpi.com/2073-4360/15/7/1660", "note": "Brief's search summary only; the page returned 403, so unverified." }, { "title": "Texin 985 datasheet", "url": "https://sushengpolymer.com/media/pdf/phFiH7_Texin-985.pdf", "note": "From the brief; gasket stiffness and cold modulus." } ], "review": { "id": "swing-bolt-wing-nut", "verdict": "corrected", "peak_clamp_force_N": 1100, "sustained_clamp_force_N": { "low": 250, "typical": 400, "high": 600 }, "scores": { "seal_suitability": 7, "outdoor_durability": 7, "printability": 7, "usability": 4 }, "issues": [ "The sustained force is whatever the user's hand makes it. F = T/(K d) on M5 gives 333-667 N at 0.5-1.0 N m with K = 0.3 (dry A2/A4 on A2), and 500-1,000 N with K = 0.2. K scatter of 0.15-0.3 alone gives a 2x spread. A hand-tight wing nut therefore lands at or above the printed-clevis sustained limit. Without a torque-limiting knob, slip clutch or Belleville stack, 'sustained' force is not controllable. 'Easily 1.5-2 N m by hand' is overstated for a 35 mm wing span (needs ~45-55 N per tip) but 0.5-1 N m is easy.", "500 N typical is slightly high. The pin-bearing ceiling is M5, 2x7 mm = 70 mm2 x 8 MPa = 560 N (700 N at 10 MPa), and the bracket anchor and wall or lug bending must also carry it. A 14x6 mm lug at an 8 mm arm sees ~38 MPa at 400 N; it needs a ~12 mm thick section, a gusset or a screwed-on bracket. M3 screw or insert anchors into a 3-4 mm wall are not shown to carry 500 N hot. Typical lowered to 400 N, high 600 N (analyst 800 N).", "Peak 1,500 N is not supportable without testing. Hand torque is the real limiter; 1 N m on M5 at K = 0.2 gives ~1 kN, which already reaches the printed limit. Peak set to 1,100 N (range 800-1,500 N).", "Most of the 'latch' is bought stainless hardware: A2/A4 DIN 444 swing bolt, wing nut or knob, washer, pin and optional Belleville stack. The printed part is only the clevis bracket and the slot seat. Plain DIN 444 from the cited catalog is class 4.6 zinc (confirmed), which is not outdoor-grade and must be replaced by A2/A4. No load rating exists on that page.", "Preload retention: a rigid bolt loses 30-58 % of force to 85A set. The recovery is manual re-tightening, which does not meet the 'indefinite, no creep open' definition of sustained force. Wing nuts also back off in vibration and stainless-on-stainless threads gall. A Belleville stack (ks ~ kg/4 gives ~10 % loss) is needed to make the number maintenance-free.", "Clevis ears: net tension at 700 N is 4.9 MPa (144 mm2) nominal, with a pin-hole Kt of ~2.5 on top. Integral clevis on an upright-printed box tears at ~340 N or less (interlayer 2 MPa, standing ASA 30 % of lying), so the separate lying-printed bracket is mandatory. Correctly flagged by the analyst but it limits where this can be used.", "Usability 4 is fair: 4-6 wing nuts, several turns each, and a 14 N per wing tip effort at 500 N. Not a quick-release closure.", "The MDPI pin-bearing paper (189 MPa / 3.6 kN) is short-term ABS/PLA coupon data, and it could not be opened, so it must not be used for sustained design." ], "confidence": "low", "reviewer_notes": "Independent recomputation. Preload F = T/(K d): M5 at 0.5/1.0/1.5 N m gives 500/1,000/1,500 N at K = 0.2, 333/667/1,000 N at K = 0.3, 667/1,333/2,000 N at K = 0.15; M4 at 0.5 N m gives 625 N at K = 0.2 (analyst arithmetic is correct). Bearing M4 2x6 = 48 mm2 (384-480 N at 8-10 MPa), M5 2x7 = 70 mm2 (560-700 N), M5 2x8 = 80 mm2 (640-800 N) also correct. My changes come from (a) the user-controlled torque issue, (b) the unchecked lug/wall/anchor bending, and (c) the fact that the brief's bearing rule is itself an untested judgement. Sources: Optimas M3/M4/M5/M6 = 2.92/5.10/8.23/11.6 kN (confirmed; no A2-70 values). Aspen DIN 444 M5x35: class 4.6, zinc plated, 5 mm eye (5.00-5.03), min tensile 400 MPa, no load rating (confirmed). CNC Kitchen carbon-fibre nylon page: M4 at 0.8 N m, ~1 week, PA6 re-tightened almost daily, PA12 once after ~half a week, and PA12 creep similar to PLA and ASA - consistent with the analyst's wording, but the page gives no re-tighten counts for ASA or PLA, so the brief's 'ASA and PLA needed about one' is not on the page, and the test is at room temperature. filamentspecs: 11.5 % vs 3 % preload loss in 7 days, conditions unstated. CNC Kitchen hook tests confirmed (ASA 57 vs 17 kg). MakerWorld Tough Case 2385298 returned HTTP 403, so the only printed-latch-plus-85A-TPU precedent has no verifiable force or IP data. WebSearch budget was exhausted, so no additional swing-bolt or wing-nut torque data could be sought. Seal suitability trimmed 8 to 7 (user-set force, no stop, K scatter). Outdoor durability trimmed 8 to 7 (hand over-tightening and a hot printed clevis at the limit; stainless galling).", "dead_or_misquoted_sources": [ "https://mdpi.com/2073-4360/15/7/1660 - HTTP 403 to me too; 189 MPa bearing and 3.6 kN fracture figures unverified, and they are short-term ABS/PLA coupon data.", "https://www.makerworld.com/en/models/2385298 - HTTP 403; Tough Case PETG snap-latch / 85A gasket model could not be opened.", "https://www.cnckitchen.com/blog/carbon-fiber-nylon-in-3d-printing-pa6-vs-pa12-tested - the page does not give re-tighten counts for ASA or PLA (brief says about one); it only says PA12 creep was similar to PLA and ASA. Room temperature, M4, 0.8 N m.", "https://filamentspecs.com/creep-resistance-3d-printed-parts/ - 11.5 % vs 3 % confirmed, but no bolt size, torque or temperature stated and no ASA data.", "https://www.aspenfasteners.com/m5-0-8-x-35mm-din-444-type-b-metric-precision-swing-eye-bolts-steel - confirmed, but it is a class 4.6 zinc part with no load rating, so it supports geometry only, not strength or outdoor suitability." ] } }, { "id": "baseline-screws", "name": "Baseline: lid screws into heat-set inserts or captive nuts", "working_principle": "A steel M3/M4 screw with a hardened washer pulls the lid into a brass heat-set insert (or a nut in a bottom pocket) in a printed boss. Preload is set by tightening torque and held by thread friction, so it self-locks and can be re-tightened. The steel is never the weak link. The boss around the insert and the washer seat on the lid are. Adding a metal compression-limiter sleeve moves the clamp load into steel and makes the squeeze a fixed dimension.", "mechanical_advantage": "Screw thread: M3 pitch 0.5 mm, M4 pitch 0.7 mm. Ideal MA = 2*pi*r/p = 157 for M3 at a 12.5 mm screwdriver-handle radius. With the nut-factor relation F = T/(K*d), K ~0.2 (own assumption), the effective hand-to-preload ratio is about 20:1 (17 N at 12.5 mm radius gives ~0.21 N*m, ~350 N on M3). Self-locking.", "peak_clamp_force_N": 1170, "sustained_clamp_force_N": { "low": 250, "typical": 350, "high": 500 }, "limiting_factor": "Printed boss and washer bearing seat, not the screw. Insert pull-out in the printed boss caps the peak at ~1.17 kN (PETG, 23 C). The sustained limit is the plastic bearing/pull-out stress at 60-70 C, so the practical limit is about 350 N per screw. Preload also decays over days to weeks: gasket compression set and plastic creep remove roughly 35-55 % of a fixed-travel preload after hot sun unless a spring is added or the screw is re-tightened.", "force_basis": "measured", "calculation": "[Web search budget was exhausted this run, so no new targeted searches were possible. I re-fetched and confirmed the CNC Kitchen, filamentspecs and Hackaday pages; other inputs come from the brief.]\n1) Washer bearing area (assumed hardware): M3 with DIN 9021 washer, OD 9 / ID 3.4 mm: 54 mm2. M4 with ISO 7089 washer, OD 9 / ID 4.3 mm: 49 mm2. Use ~50 mm2.\n2) Bearing limit under the washer (compression normal to layers, bearing allowable 5-10 MPa at 60-70 C per the brief's working rule): 50 mm2 x 5 / 7 / 10 MPa = 250 / 350 / 500 N.\n3) Insert pull-out, MEASURED (CNC Kitchen, PETG, M3, 4 perimeters, 100 % infill, n=3, hole axis along Z, i.e. the pessimistic orientation): Ruthex insert 119 kg = 1167 N, torque-out 3 Nm. Direct screw 118 kg (1158 N), strip torque 1 Nm. Helicoil 120 kg. Side-pocket nut 86 kg = 844 N. Bottom-pocket nut 166 kg = 1628 N. SF 2 on the insert: 583 N at 23 C. Hot derate 0.5-0.7 (own judgement, PETG is near its HDT of 68 C; ASA should do better): 290-410 N. Side-pocket nut with SF 2: 420 N.\n4) Steel: M3 class 8.8 proof 2.92 kN, M4 5.10 kN. Not limiting.\n5) Result: peak = 1170 N (insert pull-out). Sustained 250 / 350 / 500 N. The low value is cautious plastic stress in hot ASA or PETG. The high value needs a large washer or sleeve, ASA or PC, and a bottom-pocket nut or deep insert.\n6) Torque needed: T = K*F*d = 0.2 x 350 N x 3 mm = 0.21 N*m (M3), or 0.28 N*m (M4). This is far below the 3 Nm insert torque-out. A hand on a 12.5 mm handle radius needs ~17 N.\n7) Preload retention (own calc). Chain stiffness excluding the gasket: lid under washer 1.8 GPa x 50 mm2 / 4 mm = 22 kN/mm, boss annulus 1.8 GPa x 59 mm2 / 8 mm = 13 kN/mm, steel screw 126 kN/mm. In series this is ~8 kN/mm. Design-rib gasket, 3 N/mm over a 100 mm pitch at 0.48 mm squeeze: ~0.63 kN/mm secant. Loss = set x km/(kg+km) = 0.93 x set. Compression set 16-19 % at 23 C (Texin) gives ~15-18 % loss. Set at 70 C of 35 % (Elastollan C85A55) to 52 % (Ultrafuse) gives ~33-48 % loss. Plastic creep adds on top: PETG bolted joints lost 11.5 % preload in 7 days at room temperature against 3 % for PLA (filamentspecs).\n8) Cold: with the screw position fixed, force scales with the series stiffness. Gasket modulus x2.2 at -30 C gives ~2.0x the closing force (own calc), so do not set preload at the hot end of the range.\n9) Fit to the requirement: 350 N typical equals 100 mm pitch x 3.5 N/mm. With a 2.8 kN total this means 8 latches at typical capacity and 6 latches only at the high end.", "operating_force_N": 17, "preload_retention": "Poor to fair for the fixed rigid joint. Expect ~15-18 % loss after cool-weather settling and ~35-55 % after hot sun (gasket set at 70 C plus plastic creep), mostly in the first days. A re-tighten after the first hot cycle restores it, and later losses are smaller as the gasket set saturates. TPU stress relaxation is not included (unmeasured). A steel compression sleeve stops the plastic seat creeping but does not stop gasket set.", "adjustable_preload": true, "positive_compression_stop": true, "scores": { "seal_suitability": 7, "outdoor_durability": 8, "printability": 9, "usability": 3 }, "best_materials": "ASA is the default for the boss and lid flange. UV-stabilised PC probably raises the sustained limits ~1.3-1.5x (own judgement, unmeasured). Avoid PETG for sustained load at 60-70 C: HDT 68 C and 11.5 % preload loss in a week at room temperature. Avoid PA6-CF outdoors (3.33 % water uptake, -22 % XY strength). PAHT-CF is acceptable but still creeps.", "hardware": "Flagged: the screw, insert and washer are not printed. A2/A4 stainless M3-M4 pan or cap screws, brass heat-set inserts (Ruthex-type with deep knurling) or A2 nuts in bottom pockets, A2/A4 DIN 9021 washers, and optional stainless or brass compression-limiter sleeves. The positive stop only holds with the sleeve or a printed standoff.", "design_guidelines": [ "Boss: OD >= 12 mm for M3 and >= 14 mm for M4. Keep >= 3 mm of wall around the insert, which is 7-8 perimeters of 0.4 mm. Use 100 % infill in the boss and 4+ perimeters elsewhere. Tie the boss to the wall with 2-3 ribs of 1.6-2 mm and a root fillet R >= 2 mm.", "Print the boss with its hole axis along Z. This is the orientation CNC Kitchen tested (119 kg in PETG), and it gives round holes. Do not rely on a horizontal-axis boss.", "Insert hole: follow the maker's sheet. For Ruthex M3 use 4.0 mm drilled, or ~4.2 mm in CAD for an as-printed hole (printed holes come out 0.1-0.25 mm small). Print a calibration coupon per printer and material. Leave 2-3 mm of blind depth below the insert. Melt in at 210-240 C and press flush with a straightener.", "Choose inserts with deep knurling. CNC Kitchen saw a shallow-knurl eBay insert rotate in softer ASA.", "Lid hole: 3.4 mm clearance for M3 and 4.5 mm for M4, counterbored for a washer with OD >= 9 mm. Fit a stainless or brass compression sleeve of length = flange thickness minus the design squeeze. This gives a hard stop beside each screw. Also add a printed stop at 0.75-0.8x the free bead height.", "Set the torque limit to 0.3 N*m for M3 and 0.4-0.5 N*m for M4 (~400-500 N). Never use the direct-screw strip torque (1 Nm) as a target. Re-tighten after the first hot day and again after the first week.", "Place the screws outside the gasket line, or add an O-ring or sealing washer if they sit inside it. A through-hole in the lid is a leak path.", "Screw pitch is set by rim bending, not by screw strength: ~28 mm on a flat 3 mm lid edge, ~110 mm with a 20 mm skirt (brief's calc). Stiffen the rim before adding screws.", "Add a 2-3 mm chamfer or fillet at every internal corner. ASA is brittle at -30 C (3 kJ/m2 notched)." ], "failure_modes": [ "Insert pull-out or layer delamination in the boss under hot sustained load.", "Layers split under bolt and washer clamping. A bolt-clamped PLA lid did this in the Hackaday log.", "Washer indents into the lid flange and preload is lost.", "Preload decays from gasket compression set and plastic creep. This is the main field failure.", "Over-torque strips the direct-screw version at ~1 Nm.", "Water enters through the lid screw hole.", "The boss root cracks in the cold at sharp corners.", "Zinc-plated hardware rusts (12-72 h salt spray). Use A2/A4 stainless.", "Users leave screws loose." ], "existing_designs": [ { "title": "Hackaday.io project 12125, log 41900: PLA instrument housing with bolt-clamped lid", "url": "https://hackaday.io/project/12125/log/41900", "note": "Cautionary example. The printed layers split under bolt and washer clamping and the author tried an epoxy coating. Not a sealed or outdoor design. Verified by fetch." } ], "sources": [ { "title": "CNC Kitchen: helicoils, threaded inserts and embedded nuts (PETG M3)", "url": "https://www.cnckitchen.com/blog/helicoils-threaded-insets-and-embedded-nuts-in-3d-prints-strength-amp-strength-assessment", "note": "Verified by fetch: 118/119/120 kg direct/Ruthex/Helicoil, side-pocket nut 86 kg, bottom-pocket ~166 kg, torque-out 1/3/1/2 Nm, 4 perimeters 100 % infill." }, { "title": "CNC Kitchen: threaded inserts, cheap vs expensive (PLA M3)", "url": "https://www.cnckitchen.com/blog/threaded-inserts-for-3d-prints-cheap-vs-expensive", "note": "Verified by fetch: Ruthex 181 kg at 4.0 mm, eBay 157 kg, cheap moulded 39 kg, direct screw 142 kg. Torque-out 3-4 Nm for inserts, ~1 Nm direct. Shallow-knurl insert rotated in ASA." }, { "title": "CNC Kitchen: are our heat-set insert datasheets wrong?", "url": "https://www.cnckitchen.com/blog/are-our-heat-set-insert-datasheets-wrong", "note": "Verified by fetch: ~1400 N average at 3.6 mm hole (PLA). About 4.2 mm CAD recommended for as-printed M3 holes. Printed holes ~0.25 mm small." }, { "title": "filamentspecs: creep resistance of 3D printed parts", "url": "https://filamentspecs.com/creep-resistance-3d-printed-parts/", "note": "Verified by fetch: bolted-joint preload loss ~11.5 % PETG vs ~3 % PLA in 7 days. Bolt size, torque and temperature are not stated on the page." }, { "title": "CNC Kitchen: carbon fiber nylon, PA6 vs PA12 tested (bolt creep)", "url": "https://www.cnckitchen.com/blog/carbon-fiber-nylon-in-3d-printing-pa6-vs-pa12-tested", "note": "Verified by fetch: M4 at 0.8 N*m, ~1 week. PA6 needed re-tightening almost daily and PA12 once. The page says PA12 behaved like PLA and ASA but gives no ASA-specific count, so the brief's 'ASA ~1 re-tighten' is comparative only." }, { "title": "CNC Kitchen: comparing PLA, PETG and ASA (Prusament)", "url": "https://www.cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament", "note": "Verified by fetch: hook test lying/standing PLA 73/40 kg, PETG 55/25 kg, ASA 57/17 kg. Oven: PETG fails ~85 C, ASA ~120 C." }, { "title": "Optimas: ISO metric thread proof loads", "url": "https://international.optimas.com/technical-resources/iso-metric-thread-proof-loads", "note": "From brief, not re-fetched. M3/M4/M5 class 8.8 proof 2.92/5.10/8.23 kN." }, { "title": "Texin 985 datasheet (TPU 85A compression set)", "url": "https://sushengpolymer.com/media/pdf/phFiH7_Texin-985.pdf", "note": "From brief, not re-fetched. Compression set 16-19 % at 23 C and 40-80 % at 70 C." } ], "review": { "id": "baseline-screws", "verdict": "corrected", "peak_clamp_force_N": 900, "sustained_clamp_force_N": { "low": 120, "typical": 250, "high": 400 }, "scores": { "seal_suitability": 6, "outdoor_durability": 8, "printability": 9, "usability": 3 }, "issues": [ "Sustained 350 N typical is too high. It takes the PETG/23 C insert pull-out (1167 N), halves it for SF 2, then applies only a 0.5-0.7 hot derate. That skips two factors the brief's own working rule includes: ASA delaminates earlier than PETG (standing hook 17 vs 25 kg, ratio 0.68) and long-term creep. The brief's rule (3-5 MPa against ~40 MPa short term) is a total factor of about 0.12. Applied to 1167 N it gives about 100-200 N for an M3 insert. The washer-bearing check is fine and not limiting (50 mm2 x 8-10 MPa = 400-500 N).", "Insert-limit cross-check: the M3x5.7 Ruthex has a knurl OD of ~4.6 mm, so ~80 mm2 of lateral area. 1167 N is ~14 MPa average at room temperature. At a 2-3 MPa hot sustained allowable that is 160-250 N. An M4x8 insert has about 1.7x the area, so ~300-430 N. Typical 250 N is a compromise. A rigid screw is displacement-controlled, so creep relaxes the preload instead of rupturing the boss, which supports the upper end.", "Peak 1170 N is a measured number for a different object: an insert in a flat PETG test bar at 23 C, n=3, not a latch and not ASA. Using ASA/PETG = 0.68-1.0 gives 800-1170 N, so 900 N is a safer figure. The 'measured' label applies to the component only, not to the latch.", "Claim 'hole axis along Z, i.e. the pessimistic orientation' is not on the cited CNC Kitchen pages. Both the PETG helicoil page and the PLA insert pages leave the pull-out orientation unstated (the PETG page says only 'flat test pieces, 4 perimeters, 100 % infill'). Treat the orientation as inferred, not tested.", "The 11.5 % PETG vs 3 % PLA preload loss is second-hand. filamentspecs takes it from the control groups of an MDPI Polymers 2021 accelerated-aging study (compression creep). The page states no bolt size, torque or temperature. 'Bolted joints at room temperature' is the analyst's gloss, and MDPI returned HTTP 403, so the primary was not checked.", "Preload-loss range is truncated at the hot end. It uses Elastollan 35 % and Ultrafuse 52 % set at 70 C, but the brief's Texin 985 sheet (re-read) gives 40 % and 80 % at 70 C/22 h. A rigid joint can therefore lose 33-74 %, not 33-48 %. Retained force after hot sun without a re-tighten is roughly 25-65 % of the assembly preload. The 250 N figure is capacity at assembly, not what is still clamping in August.", "Torque-controlled preload scatters about +/-30 % because the nut factor K is assumed at 0.2 (real range 0.15-0.3). Without a metal sleeve there is no hard stop, so the 'positive compression stop = true' flag only holds with the sleeve.", "Seal score cut from 7 to 6: the rigid joint loses most of its force in hot sun and needs a re-tighten routine, and the preload scatter is large. Usability 3 stands (6-11 screws to open)." ], "confidence": "medium", "reviewer_notes": "Independent recalculation. Hand force: M3 at 0.21 N*m is 17 N at 12.5 mm radius, checked. K = 0.2 gives 350 N, but the correct preload for this boss is ~250 N, i.e. about 0.15 N*m. Washer area (OD 9 / ID 3.4): 54 mm2, checked. Joint stiffness chain: lid 22.5, boss 13.3, screw 126 kN/mm in series gives 7.8 kN/mm, checked. Gasket secant 300 N / 0.48 mm = 0.625 kN/mm, so loss = 0.93 x set, checked. Hold-down count: 2.8 kN / 250 N = 11 screws at 63 mm pitch, which is fine against rim bending only if the rim is stiffened. At the 8-latch reference the screws cover the low load window (175 N each) but not the high one (350 N each). Sources opened: CNC Kitchen PETG insert page confirmed (118/119/120 kg, side nut 86, bottom nut ~166, torque-out 1/3/1/2 Nm, n=3 pull-out, 4 perimeters 100 % infill). CNC Kitchen cheap-vs-expensive page confirmed (Ruthex 181, eBay 157, cheap 39, direct 142 kg PLA; shallow-knurl eBay insert rotated in ASA). CNC Kitchen datasheet page confirmed (~1400 N, 4.2 mm CAD hole, knurl OD ~4.6 mm). Optimas confirmed (M3 2.92, M4 5.10, M5 8.23 kN). Texin 985 PDF decoded locally and confirmed (D575 table, set 16/19 % at 23 C, 40/80 % at 70 C, flexural 26.9 vs 59.0 MPa, Vicat 80 C). Ultrafuse TDS confirmed (26 % and 52 %). Elastollan C85A55 confirmed (25 % and 35 %, Vicat 110 C). Hackaday log confirmed in substance, but it is a PLA profiler cap/collar with eye bolts, not a lid. CNC Kitchen carbon-nylon page: no ASA re-tighten count, only 'PA12 once, similar to PLA and ASA', so the analyst's own caveat is right. No new web searches were possible (search budget exhausted); all checks used WebFetch and local PDF decoding.", "dead_or_misquoted_sources": [ "https://www.cnckitchen.com/blog/helicoils-threaded-insets-and-embedded-nuts-in-3d-prints-strength-amp-strength-assessment : numbers correct, but the pull-out orientation (hole axis along Z) is not stated on the page", "https://filamentspecs.com/creep-resistance-3d-printed-parts/ : 11.5 % / 3 % are secondary figures from an MDPI Polymers 2021 aging study (compression creep, controls); the page gives no bolt size, torque or temperature, so 'bolted joint at room temperature' is not supported", "https://www.mdpi.com/2073-4360/13/23/4132 : HTTP 403, primary for the 11.5 % figure not checked", "https://www.cnckitchen.com/blog/carbon-fiber-nylon-in-3d-printing-pa6-vs-pa12-tested : gives PA12 one re-tighten and PA6 near-daily; no ASA count, so the brief's 'ASA about one re-tighten' is only comparative", "https://hackaday.io/project/12125/log/41900 : the part is a PLA cap/collar with eye bolts, not a bolt-clamped lid" ] } }, { "id": "captive-screw-spring-stack", "name": "Captive stainless screw clamp with spring or Belleville stack and metal insert", "working_principle": "A captive A4 stainless M4 thumbscrew pulls the lid into a heat-set insert through a stiff spring or disc-spring stack under the head. The spring is about 2-4x softer than the gasket, so the gasket squeeze is set by spring force instead of fixed travel. A few hundredths of a millimetre of gasket set or plastic creep then changes the preload very little. The load path is steel except for the boss, the washer seat and the lid flange.", "mechanical_advantage": "Screw thread, M4 pitch 0.7 mm. Ideal MA = 2*pi*r/p = 112 at a 12.5 mm knob radius. With K ~0.2 the real hand-to-preload ratio is ~16:1 (22 N at 12.5 mm gives ~0.28 N*m, ~350 N). Friction under a rotating spring end adds torque, so put a thrust washer between spring and knob. The stack converts tight position tolerance into force tolerance: stiffness ratio ks/kg = 1/4 gives 4x the screw travel for the same force.", "peak_clamp_force_N": 1200, "sustained_clamp_force_N": { "low": 250, "typical": 350, "high": 500 }, "limiting_factor": "The same printed boss, insert and washer seat as baseline-screws (~350 N typical). The spring does not raise the force limit. It keeps the force from decaying and from rising in the cold. Practical limit: a spring soft enough to help (ks ~ kg/4 = ~150 N/mm for a 100 mm pitch and 3 N/mm line load) is a heavy die spring or Belleville stack, not a small coil. Coil springs work only for light loads of about 150 N or less.", "force_basis": "calculated", "calculation": "[Web search budget was exhausted this run; no new targeted searches. Boss and insert limits come from the CNC Kitchen tests I re-fetched. The spring model is my own calculation.]\n1) Boss limits are the same as baseline-screws. M4 insert and washer seat: 250 / 350 / 500 N sustained. Peak ~1.2 kN, taken from the measured M3 PETG insert (1167 N) because I found no M4 printed-host test. A vendor insert paper cites 2.7 kN for M4 but is low confidence.\n2) Gasket stiffness per latch, design rib: 3 N/mm x 100 mm pitch = 300 N at 20 % of 2.4 mm = 0.48 mm, which gives kg = 625 N/mm secant (about 800 N/mm at 3.9 N/mm).\n3) Spring rate: ks = kg/4 = 156 N/mm. At 300 N the spring deflects 1.9 mm. Total screw travel = 0.48 + 1.9 = 2.4 mm, about 3.4 turns of M4. Compromise ks = kg/2 = 312 N/mm needs 0.96 mm of spring deflection.\n4) Spring-type check. Coil spring rate k = G*d^4/(8*D^3*N), G ~69 GPa for 302 stainless. For d=1.6 mm, D=9 mm, 1.5 active coils: ~52 N/mm, which suits 50 mm pitch and 2 N/mm (~100 N). For 156 N/mm with d=2 mm and D=10 mm I get less than 1 active coil, which is impractical. So use a die spring, a wave spring or a Belleville stack. Series discs add travel and parallel discs add force. Check against the spring maker's table; I did not source disc spring catalog values.\n5) Preload loss from gasket set: loss = set x ks/(kg+ks). With ks = kg/4 this is 0.2 x set. With ks = kg/2 it is 0.33 x set. Set of 19 % (23 C Texin) gives 3.8 % / 6.3 %. Set of 35-52 % (70 C Elastollan / Ultrafuse) gives 7-10 % / 12-17 %, against ~33-48 % for the rigid joint (baseline).\n6) Plastic creep of the member stack, 0.04 mm assumed: with the spring, dF = 125 N/mm x 0.04 mm = 5 N (1.7 %). With a rigid joint it is ~580 N/mm x 0.04 mm = 23 N (8 %).\n7) Cold: series stiffness rigid joint 580 -> 1173 N/mm (x2.0). Spring chain 125 -> 140 N/mm (x1.12) when the gasket stiffens 2.2x at -30 C. The stack removes most of the cold overload.\n8) Torque: T = 0.2 x 350 N x 4 mm = 0.28 N*m, ~22 N at a 12.5 mm knob.\n9) Spring materials: 302/304 stainless is rated to ~288-316 C and is 25-30 % weaker than music wire, which rusts and is limited to ~121 C (Lee Spring, re-fetched). 17-7PH or 316 are alternatives.\n10) Caveat: a vendor says Belleville washers cut preload loss to under 1 % in steel joints, but that is not validated for plastics, and disc stacks help less in thermally cycled creeping joints. Test on the real boss. I could not re-read the Solon PDF.", "operating_force_N": 22, "preload_retention": "Good. Calculated ~90-96 % retained with ks = kg/4 and ~83-94 % with ks = kg/2 after 70 C compression set (35-52 %), against 52-67 % for a rigid joint. The cold force rise is ~12 % instead of ~100 %. Not included: TPU stress relaxation, spring relaxation at 70 C, and stack friction hysteresis (all unmeasured). No printed-host test of this arrangement was found.", "adjustable_preload": true, "positive_compression_stop": false, "scores": { "seal_suitability": 9, "outdoor_durability": 8, "printability": 8, "usability": 5 }, "best_materials": "ASA for the boss and lid flange. UV-stabilised PC probably raises the sustained limits ~1.3-1.5x (own judgement). Avoid PETG and PETG-CF at 60-70 C, and avoid PA6-CF outdoors. Use A4 stainless for the screw and 302/316/17-7PH for the spring or discs.", "hardware": "Flagged: not printed. A4 stainless M4 thumbscrew or screw with knob, brass heat-set insert, stainless die/wave spring or 17-7PH/316 Belleville stack, hardened stainless thrust washer, retaining clip or captive O-ring, optional hardened spacer sleeve.", "design_guidelines": [ "Size the spring to the gasket. Target ks = kg/4 to kg/2, where kg = F/delta of the design rib per latch (e.g. 625 N/mm for 3 N/mm at 100 mm pitch and 0.48 mm squeeze). Use coil springs only for loads of about 150 N or less. Above that use a die spring, wave spring or Belleville stack.", "Screw travel must cover gasket squeeze plus spring deflection plus ~30 % margin: ~3.5 mm for a 300 N latch. Use a thread engagement of at least 2 x d.", "A hardened spacer sleeve under the head sets the maximum spring compression at 1.3-1.5x the nominal load, so over-tightening cannot crush the gasket or the boss.", "Seat the spring on a stainless washer with OD at least equal to the spring OD (9-12 mm). Never seat it on bare printed plastic, which creeps under the spring seat.", "Make the screw captive with an E-clip, a retainer ring or an O-ring in the lid hole. A dropped thumbscrew outdoors is a failure.", "Boss, insert and hole sizes as baseline-screws: boss OD >= 14 mm for M4, 100 % infill, hole axis along Z, root fillet >= 2 mm, ribs 1.6-2 mm.", "Add a printed land stop at 0.75-0.8x the free bead height beside each latch. The spring defines the force and the stop caps over-tightening.", "Put a cap over the spring pocket, or a drain hole, so dirt and ice do not bind the stack. Do not use music wire outdoors.", "Pitch is set by rim bending (~28 mm on a flat 3 mm edge, ~110 mm with a 20 mm skirt). Stiffen the rim before adding screws." ], "failure_modes": [ "Insert pull-out or boss delamination under sustained hot load. This is the same limit as baseline-screws.", "The spring goes solid, so the joint becomes rigid and loses its benefit. This happens when the user over-tightens or the spring is sized too small.", "Spring or stack friction and hysteresis change the actual preload by 10-30 % (own estimate).", "Music-wire springs rust. Stainless springs relax slightly at 70 C.", "Dirt or ice in the spring pocket binds the stack.", "The captive retainer fails and the screw is lost.", "The disc stack tilts and sticks on the screw.", "The lid screw hole is a water ingress path.", "The boss root cracks in the cold at sharp internal corners." ], "existing_designs": [], "sources": [ { "title": "CNC Kitchen: helicoils, threaded inserts and embedded nuts (PETG M3)", "url": "https://www.cnckitchen.com/blog/helicoils-threaded-insets-and-embedded-nuts-in-3d-prints-strength-amp-strength-assessment", "note": "Verified by fetch. Boss and insert limits used for the force ceiling." }, { "title": "Lee Spring: music wire vs stainless steel", "url": "https://www.leespring.com/music-wire-versus-stainless-steel", "note": "Verified by fetch: music wire ~121 C, rusts when wet, strength above 400 ksi. 302/304 stainless up to ~288-316 C, 275-300 ksi." }, { "title": "filamentspecs: creep resistance of 3D printed parts", "url": "https://filamentspecs.com/creep-resistance-3d-printed-parts/", "note": "Verified by fetch. PETG joints lost ~11.5 % preload in 7 days against ~3 % for PLA." }, { "title": "Elastollan C85A55 datasheet (TPU 85A compression set)", "url": "https://sushengpolymer.com/media/pdf/yKRdOr_Elastollan-C85A55.pdf", "note": "From brief, not re-fetched. 25 % set at 23 C and 35 % at 70 C. Used for the loss calc." }, { "title": "Texin 985 datasheet", "url": "https://sushengpolymer.com/media/pdf/phFiH7_Texin-985.pdf", "note": "From brief, not re-fetched. Set 16-19 % at 23 C and 40-80 % at 70 C. Modulus x2.2 at -30 C." }, { "title": "SPIROL: maintaining joint integrity when converting from metal to plastic", "url": "https://uk.spirol.com/assets/files/ins-wp-how-to-maintain-joint-integrity-when-converting-from-metal-to-plastic-us.pdf", "note": "From brief, not re-fetched. Plastic joints lose clamp load as thickness creeps and metal inserts do not." }, { "title": "Solon: combatting embedment relaxation in bolted joints", "url": "https://www.solonmfg.com/documents/Combatting%20Embedment%20Relaxation%20in%20Bolted%20Joints%20-February%202025%20Final%20Version.pdf", "note": "Vendor claim for steel joints. The fetch returned raw PDF only, so I could not re-read it. Not validated for plastics." }, { "title": "ASME PVP2008: Belleville washers to reduce load loss in flange joints", "url": "https://www.sciencegate.app/document/10.1115/pvp2008-61005", "note": "From brief, not re-fetched. Metal flange context." } ], "review": { "id": "captive-screw-spring-stack", "verdict": "corrected", "peak_clamp_force_N": 900, "sustained_clamp_force_N": { "low": 110, "typical": 220, "high": 380 }, "scores": { "seal_suitability": 8, "outdoor_durability": 7, "printability": 8, "usability": 4 }, "issues": [ "Sustained was set equal to the rigid screw (350 N). That is wrong in the direction that matters. The spring makes the boss force-controlled: it holds about the full preload at 60-70 C for months instead of relaxing, so the insert and boss creep-rupture margin is lower than for the rigid screw, not equal. Same boss limits as baseline-screws, minus a small allowance for constant load: typical 220 N.", "The spring helps the seal, not the force ceiling. The preload-retention figures (83-96 % retained) are own calculation only. They ignore spring relaxation at 70 C, stack friction and hysteresis (the analyst's own 10-30 % estimate), TPU stress relaxation, and the 80 % hot set in the Texin sheet. With ks = kg/4 and 80 % set the loss is 16 %, with ks = kg/2 it is 27 %. Seal 9 is not supportable on unvalidated numbers, so 8.", "Hardware reality: ks about 150 N/mm for 300 N at ~2 mm deflection is a die spring or a Belleville stack of 8-10 discs in series. Coil-spring check: G*d^4/(8*D^3*N) for d=2, D=10 mm gives N = 0.88 active coils for 156 N/mm, so the analyst's 'impractical' is right. Shear stress at 300 N in a d=2/D=10 coil is about 1.2 GPa corrected, so it also overstresses the wire. Stainless disc stacks tilt, stick and bind with dirt or ice outdoors, and the durability score falls to 7.", "Usability 5 is generous: about 5 turns of a small captive thumbscrew to 0.28 N*m (22 N at a 25 mm knob), a retainer, and no feel for the end of travel. Set to 4.", "Peak 1200 N is above the baseline and is taken from an M3 PETG insert at 23 C with no M4 data. Cap it at 900 N like baseline-screws.", "The Solon 'Belleville cuts preload loss below 1 %' claim is unreadable (the PDF has no extractable text) and applies to steel joints. SPIROL says only that plastics lose clamp load and metal inserts do not. ASME PVP2008 on sciencegate returned 403. None of these supports a number for a plastic boss." ], "confidence": "low", "reviewer_notes": "Recomputed the spring maths. Gasket kg = 3 N/mm x 100 mm / 0.48 mm = 625 N/mm, checked. Loss = set x ks/(kg+ks): ks = kg/4 gives 0.2 x set, ks = kg/2 gives 0.33 x set, checked. Cold factor for the stack, 125 to 140 N/mm, is arithmetically right (about +12 %), but it applies the flexural-modulus ratio 59.0/26.9 = 2.2 (verified in Texin) to a compressive stiffness, which is only an approximation, and -30 C is below the -20 C reference. Screw travel (0.48 + 1.9 mm) x 1.3 is about 3.1-3.5 mm and engagement of 2d is about 8 mm, so the boss needs 11 mm or more of thread depth, which the guidelines do not state. Torque 0.28 N*m at K=0.2 is right, and friction under a rotating spring end adds to it. Lee Spring page confirmed: music wire 121 C, rusts when wet, 302/304 stainless 275-300 ksi against 400+ ksi (25-30 % weaker), stainless rated 288-316 C. Boss limits were verified with the same CNC Kitchen pages as baseline-screws. The reason for the lower force, in one line: a spring-loaded joint cannot relax away its overload the way a rigid joint can, so the boss carries the full load continuously. Best use: a stainless Belleville stack or die spring under a washer, with a printed hard stop and a re-torque on the first hot day.", "dead_or_misquoted_sources": [ "https://www.solonmfg.com/documents/Combatting%20Embedment%20Relaxation%20in%20Bolted%20Joints%20-February%202025%20Final%20Version.pdf : text not readable; the under-1 % figure cannot be verified, and steel-joint context in any case", "https://www.sciencegate.app/document/10.1115/pvp2008-61005 : HTTP 403, unverified", "https://uk.spirol.com/assets/files/ins-wp-how-to-maintain-joint-integrity-when-converting-from-metal-to-plastic-us.pdf : qualitative only (plastic creep and relaxation, metal inserts do not creep); no quantified preload loss, no spring data", "https://filamentspecs.com/creep-resistance-3d-printed-parts/ : secondary figure from an MDPI aging study; conditions not stated" ] } }, { "id": "vise-action-screw-cam", "name": "Vise-action / lift-and-turn compression latch (cam plus screw take-up)", "working_principle": "A lift-and-turn or T-handle turns a steel stud. A helical ramp between the handle hub and the housing, or between the pawl and the keeper, converts about 90 degrees of rotation into 1-1.5 mm of axial draw. A pawl hooked behind the frame pulls the lid down onto the gasket. A screw or nut on the stud sets the grip range. The load path is steel stud, printed pawl or ramp, printed or steel keeper.", "mechanical_advantage": "Two stages. (1) Grip adjustment: M5 nut, pitch 0.8 mm, set once. (2) Ramp: mean radius 8 mm, rise 1.5 mm in 90 degrees, tan(alpha) = 1.5/12.57 = 0.119 (6.8 degrees). Frictionless MA = 50 mm lever / (8 mm x 0.119) = 52. With mu = 0.3 the real ratio is ~14:1 (21 N at 50 mm gives ~1.04 N*m, ~300 N). Self-locking requires mu > tan(alpha) = 0.119. Grease or a smooth surface can erode that margin, so add a detent.", "peak_clamp_force_N": 1000, "sustained_clamp_force_N": { "low": 150, "typical": 300, "high": 450 }, "limiting_factor": "The printed load path at the frame: the keeper, ledge or hook, and the pawl bending. With a steel keeper or insert-boss interface, the pawl bending and ramp bearing allow ~300-450 N. With a printed ledge loaded through layers (box printed upright), shear across layers limits it to ~150-300 N. A measured standing ASA hook broke at only 17 kg (167 N) at 23 C in the CNC Kitchen test, geometry not stated. The M5 stud and the lid insert are not limiting.", "force_basis": "estimated", "calculation": "[Web search budget was exhausted this run. No printed test of this mechanism type was found. Commercial ratings are static and come from the brief; the RS and Southco PDFs returned raw binary, so I could not re-read them.]\n1) Assumed printed analogue within 70 x 35 x 30 mm: steel M5 A2 stud, 60 mm lift-and-turn handle with 50 mm effective radius, ramp pair at mean radius 8 mm with 1.5 mm rise over 90 degrees. Printed pawl 20 wide x 14 thick, carrying an M5 hole (5.3 mm). Span between keeper supports 15 mm. Ramp contact 2 x (6 x 10 mm) = 120 mm2. Printed keeper ledge, root section 15 x 15 mm = 225 mm2.\n2) Ramp torque: T = F*r_m*(tan a + mu)/(1 - mu*tan a) = F x 8 mm x 0.435 = 3.48 mm x F. For 300 N this is 1.04 N*m, ~21 N at the 50 mm handle. With mu = 0.15 it is 0.66 N*m and 13 N, but the ramp then barely self-locks.\n3) Pawl bending, centre-loaded (F = 4*sigma*Z/L). Net section modulus Z = (20-5.3) x 14^2 / 6 = 480 mm3. In-plane allowable 3-5 MPa divided by Kt 1.3 for the hole gives 2.3-3.8 MPa. F = 4 x 2.3 x 480/15 = 294 N and 4 x 3.8 x 480/15 = 486 N. A pawl 18 x 12 mm gives only ~190-310 N.\n4) Printed ledge shear across layers, 1.5V/A <= 2 MPa (the brief's across-layer allowable, applied to shear as my assumption): A >= 1.5 x 300/2 = 225 mm2 for 300 N, and ~112 mm2 for 150 N.\n5) Ramp bearing, load normal to layers: 120 mm2 x 5-8 MPa = 600-960 N. Not limiting.\n6) Result: sustained 150 (printed standing ledge, small section) / 300 (steel keeper or insert boss, 20 x 14 pawl) / 450 N (large pawl, steel keeper). Peak ~1.0 kN (range 700-1200): pawl net-section break at ~35 MPa/Kt 1.5 gives ~2.9 kN, but ledge interlaminar failure and the measured standing-hook weakness cap it lower.\n7) Commercial anchor (static, not sustained, zinc/aluminium bodies): Southco N4 600 N working, 1200 N ultimate, 300 N average compression force. E3 450 N adjustable grip. M1-20 460 N short cam. 62-series 220-1250 N. Southco rates N4 and M1 as NEMA 4 / IP65-66 only with their flange or cup gasket.\n8) Preload retention is stroke-controlled like a rigid joint. Loss ~0.9 x set = 33-48 % after 70 C hot sun (35-52 % set). With a wave spring or disc stack under the nut, loss falls to ~10-17 %, but that needs ~2.4 mm of travel. Make the ramp rise 2.5-3 mm in that case. The ramp angle is then 0.19, mu 0.3 gives ~0.52 x r_m torque, and the hand force rises by about 20 %.\n9) Cold: with fixed travel the force rises ~2x at -30 C (gasket modulus x2.2), so adjust the grip at mid-temperature.", "operating_force_N": 21, "preload_retention": "Fair to poor if stroke-controlled: ~33-48 % loss after hot sun, from the 85A set (35-52 %) plus ramp and pawl creep. Better with a spring: add a wave spring or Belleville stack on the stud and lengthen the ramp rise to 2.5-3 mm, which cuts the loss to ~10-17 %. Adjustable by the stud nut, so it can be re-set after the first hot cycle. Printed ramps creep and wear (printed helical ramps are a known weak point).", "adjustable_preload": true, "positive_compression_stop": true, "scores": { "seal_suitability": 7, "outdoor_durability": 7, "printability": 6, "usability": 7 }, "best_materials": "ASA for the handle, housing, ramps and pawl. A steel (2 mm 304 stainless plate) pawl and keeper lifts the sustained limit above the printed value. UV-stabilised PC gives ~1.3-1.5x margin on printed parts (own judgement). Avoid PETG and PETG-CF at 60-70 C, and PA6-CF outdoors.", "hardware": "Flagged: not printed. A2/A4 stainless M5 stud or shoulder screw with jam nut, hardened washers, optional 304 stainless pawl and keeper plate, optional stainless wave spring or disc stack, optional brass bushing at the housing. Or buy the commercial Southco-type latch.", "design_guidelines": [ "Print the pawl lying flat so bending stress runs along layers (XY plane). The stud hole axis is along Z. Minimum pawl 20 x 14 mm in section with a 5.3 mm hole. Use 4+ perimeters and 0.2 mm layers or finer.", "Frame-side keeper: use a steel keeper, or hook onto a steel pin or a screwed insert boss (the measured insert interface gives 119 kg in Z). If it must be a printed ledge, make it at least 15 x 15 mm at the root, 12+ mm thick, with a root fillet >= 3 mm. Do not rely on a thin standing hook: 17 kg in the CNC Kitchen test.", "Ramp: rise 1.5 mm in 90 degrees for a rigid stud (or 2.5-3 mm if you add a spring stack), mean radius 8-10 mm, contact area >= 120 mm2, faces printed flat so the load is normal to layers. End the ramp in a flat dwell of about 15 degrees plus a 0.3 mm detent so the handle cannot back-drive under vibration and creep.", "Lever and hub: 50 mm effective radius. Keep the hand force at or below 25 N at the typical load. Make the handle hub captive on the stud with a hex pocket or D-flat.", "Grip adjustment: M5 jam nut on the stud and a feeler-gauge or force-gauge set-up at assembly. Add a printed land stop at 0.75-0.8x the free bead height beside each latch.", "Pawl slot in the frame flange: ~22 x 15 mm for the 20 x 14 pawl. Check the flange does not lose too much area.", "Seal the stud hole in the lid with an O-ring or boot. Put the latch where rim stiffness allows (pitch ~28 mm on a flat 3 mm edge, ~110 mm with a 20 mm skirt).", "Internal corners: R >= 1.5 mm everywhere because ASA is brittle at -30 C." ], "failure_modes": [ "The printed keeper or ledge shears across layers under sustained hot load.", "The pawl cracks at the stud hole in bending.", "Ramp wear or creep gives progressive loss of draw.", "The ramp back-drives under vibration if mu falls below tan(alpha), for example with grease or ice.", "Gasket set and plastic creep take 33-48 % of a fixed-travel preload.", "The latch is closed 'off the ramp' and the force depends on where the handle parked.", "The stud hole leaks.", "Cold: force doubles at -30 C and a printed handle can crack." ], "existing_designs": [ { "title": "Southco N4 compression latch datasheet (RS) [COMMERCIAL, not printable]", "url": "https://docs.rs-online.com/eca8/0900766b801e0b3a.pdf", "note": "600 N working, 1200 N ultimate, 300 N compression force (from brief). The PDF returned raw binary so I could not re-check the numbers." }, { "title": "Southco M1 compression latch literature [COMMERCIAL, not printable]", "url": "https://media.southco.com/media/static/Literature/m1-c.en.pdf", "note": "NEMA 4 / IP66 with flange gasket (from brief). Not re-checked: PDF unreadable via fetch." }, { "title": "Southco E3 compression latch (GlobalSpec) [COMMERCIAL, not printable]", "url": "https://datasheets.globalspec.com/ds/southco/e3-16-206/829690b1-1f4e-4eab-b06d-1ffb2d2929cb", "note": "450/300 N static (from brief). My fetch returned HTTP 403." }, { "title": "Southco 62-series datasheet [COMMERCIAL, not printable]", "url": "https://static.datasheets.com/doc/8464620-southco-62-10-23-rs-ds.pdf", "note": "220-1250 N static loads (from brief). Not re-checked." } ], "sources": [ { "title": "Southco N4 datasheet (RS)", "url": "https://docs.rs-online.com/eca8/0900766b801e0b3a.pdf", "note": "From brief via search text; fetch unreadable." }, { "title": "Southco M1 literature", "url": "https://media.southco.com/media/static/Literature/m1-c.en.pdf", "note": "From brief via search text; fetch unreadable." }, { "title": "CNC Kitchen: comparing PLA, PETG and ASA (Prusament)", "url": "https://www.cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament", "note": "Verified by fetch. ASA hook lying 57 kg vs standing 17 kg (29 %). Used for the printed-ledge anchor." }, { "title": "CNC Kitchen: helicoils, threaded inserts and embedded nuts (PETG M3)", "url": "https://www.cnckitchen.com/blog/helicoils-threaded-insets-and-embedded-nuts-in-3d-prints-strength-amp-strength-assessment", "note": "Verified by fetch. Insert in Z pull-out 119 kg." }, { "title": "Texin 985 datasheet", "url": "https://sushengpolymer.com/media/pdf/phFiH7_Texin-985.pdf", "note": "From brief, not re-fetched. Compression set and cold modulus." }, { "title": "Ultrafuse TPU 85A TDS", "url": "https://www.dream3d.co.uk/wp-content/uploads/2022/12/Ultrafuse_TPU_85A_TDS_EN_v2.5.pdf", "note": "From brief, not re-checked. Printed TPU set 26 % at 23 C, 52 % at 70 C." } ], "review": { "id": "vise-action-screw-cam", "verdict": "corrected", "peak_clamp_force_N": 700, "sustained_clamp_force_N": { "low": 100, "typical": 200, "high": 350 }, "scores": { "seal_suitability": 6, "outdoor_durability": 6, "printability": 6, "usability": 6 }, "issues": [ "Sustained 300 N typical is 50 % above my figure. The pawl bending check is right (Z = 480 mm3; F = 4*sigma*Z/L gives 294 N at 2.3 MPa and 486 N at 3.8 MPa), but the keeper side is not. The shear check for the printed ledge (1.5V/A at 2 MPa, 225 mm2 gives 300 N) ignores root bending. A hook loaded up through the layers sees sigma = 6*F*a/(b*t^2) across layers. For b=15, t=12, a=3-6 mm and 2 MPa allowable that is 120-240 N. The 'steel keeper' alternative still has to be anchored in the printed box (lug or insert boss), which is limited to the same ~150-300 N as the screw boss. Typical 200 N.", "The hand-force estimate is optimistic. T = 3.48 mm x F counts only the ramp (checked: tan(alpha)=0.119, 6.8 deg, MA 52 frictionless, ~14:1 at mu=0.3). Under tension, a rotating stud needs a second sliding interface (hub on lid, or pawl on keeper) at ~7 mm radius with mu ~0.3, which adds ~2 mm x F. Total ~5.6 mm x F gives about 22 N at 200 N (34 N at 300 N) on a 50 mm lever instead of 14-21 N. Still inside the 20-50 N band, but with less margin. A Southco N4 ('average compression force 300 N, T-handle turned by hand', verified) shows that figure is reachable by hand with a good ramp.", "Peak 1000 N is too high for a printed latch. Commercial anchors are the verified Southco N4 (600 N working / 1200 N ultimate, zinc), Southco M1 in 316 stainless (350 N long cam / 1010 N short cam max static, NEMA 4/IP66 only with the supplied flange gasket) and Southco 62-series (1250 N max static). A printed ASA latch should not claim 83 % of a zinc latch's ultimate. A printed standing ledge breaks at about 540-1080 N (across-layer ~9 MPa from the 29 % rule). Peak 700 N (range 500-1000).", "Fixed-travel force scatter. Stack-up of +/-0.2 mm against a 0.48 mm squeeze gives roughly +/-40 % force, and the nut-set grip has to be redone after the first hot day. Rigid hot loss is 33-74 % (Texin 80 % set not used by the analyst), and printed ramp creep adds to it. Seal 6.", "Printed helical ramps and a handle, with grease, ice or dirt on the ramp, are the likely field failures. mu can drop below tan(alpha) = 0.12 and back-drive under vibration. Durability 6, usability 6 (lift, turn and a one-time grip adjustment per latch).", "The 'steel pawl/keeper' tiers need cut stainless plate. That is not common hardware in the user's sense, so the 300-450 N tiers do not describe 'printable with common hardware'." ], "confidence": "low", "reviewer_notes": "Independent recalculation. Ramp: rise 1.5 mm in 90 deg at r=8 mm gives arc 12.57 mm, tan(alpha)=0.1194, T = F*8*(0.1194+0.3)/(1-0.0358) = 3.48 mm x F, checked. With the second interface, 5.6 mm x F. Pawl section: net Z = (20-5.3) x 14^2 / 6 = 480 mm3, checked. Pawl at 2.3-3.8 MPa gives 294-486 N, checked. Pawl break at 35/1.5 MPa gives 2.9 kN, arithmetic right but not governing. Ramp bearing 120 mm2 x 5-8 MPa = 600-960 N, not limiting. Keeper ledge bending (b=15, t=12): 120 N at a=6 mm and 240 N at a=3 mm at 2 MPa across layers, so the printed standing ledge is the weak link. This matches CNC Kitchen's ASA standing hook of 17 kg against 57 kg lying (verified; hook geometry unspecified on the page). Commercial anchors verified by decoding the PDFs locally: Southco N4 (RS PDF, encrypted but readable: working 600 N, average ultimate 1200 N, average compression force 300 N from a hand-turned T-handle), M1 (stainless, 1010 N short cam / 350 N long cam, IP66 with flange gasket), 62-series (1250 N). Southco E3 (GlobalSpec) returned 403 and could not be checked. No printed test of this mechanism was found, so all numbers are estimates. Fit to the requirement: at 200 N it needs 14 latches for 2.8 kN, so a 70 mm latch body does not fit around a 200 x 150 lid at the high gasket load; at the low 1.4 kN it needs 7 latches.", "dead_or_misquoted_sources": [ "https://datasheets.globalspec.com/ds/southco/e3-16-206/829690b1-1f4e-4eab-b06d-1ffb2d2929cb : HTTP 403, 450/300 N E3 claim unverified", "https://docs.rs-online.com/eca8/0900766b801e0b3a.pdf : OK once decrypted locally (600 N working, 1200 N ultimate, 300 N compression force); the WebFetch tool alone cannot read it", "https://media.southco.com/media/static/Literature/m1-c.en.pdf : the 'NEMA 4/IP66 with gasket' claim is right; static loads are 1010 N (short cam) and 350 N (long cam), which the analyst did not use", "https://static.datasheets.com/doc/8464620-southco-62-10-23-rs-ds.pdf : 1250 N is the maximum static load of the part on the page; the '220-1250 N' range is not on that single page", "https://www.cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament : hook numbers correct (PLA 73/40, PETG 55/25, ASA 57/17 kg), hook geometry not stated" ] } }, { "id": "quarter-turn-compression", "name": "Quarter-turn compression latch (steel cam and ramp, 4-6 mm draw-down)", "working_principle": "A quarter turn of a key, knob or T-handle rotates a shaft. A helical ramp or cam in a panel-mounted housing converts the rotation into axial draw. A pawl on the shaft behind the panel hooks the frame and pulls the lid onto the gasket. Commercial versions (EMKA 1000, Southco E9) use a two-stage turn for 4-6 mm of travel against foam gaskets. A printed version replaces the knob, housing and ramp with printed parts on a steel shaft, nut and washers.", "mechanical_advantage": "Ramp: mean radius 10 mm, rise 1.5 mm over 90 degrees, tan(alpha) = 1.5/15.7 = 0.0955 (5.5 degrees). Frictionless MA = 25 mm hand radius / (10 mm x 0.0955) = 26. With mu = 0.3 (dry printed ASA on ASA, assumed) the real ratio is ~6:1 (33 N at 25 mm gives ~0.81 N*m, ~200 N). Lower than a screw or lift-and-turn latch because the ramp radius is small and friction is high. Self-locking requires mu > 0.0955.", "peak_clamp_force_N": 700, "sustained_clamp_force_N": { "low": 100, "typical": 200, "high": 350 }, "limiting_factor": "The printed pawl and the printed frame ledge. The pawl must pass through the panel cutout (about 22-24 mm), so a printed pawl is small and weak in bending. A steel or hardened cam is needed. The ledge loaded through layers is the second limit. Also, the ramp stroke (4-6 mm commercial, 1-1.5 mm printed) is far from the 0.2-0.75 mm the gasket needs, so force depends on where the cam parks unless the ramp ends in a hard stop.", "force_basis": "estimated", "calculation": "[Web search budget was exhausted this run. No printed test was found. Commercial ratings come from the brief; I re-fetched the EMKA product page and the ElectronicSpecifier article.]\n1) Assumed printed analogue: steel M5 shaft with a nut and washers, printed T-knob or 50 mm wing (hand radius 25 mm), housing in a 24 mm panel cutout. Ramp pair at mean radius 10 mm, rise 1.5 mm over 90 degrees, radial width 6 mm, 12 mm arc each, area 2 x 72 = 144 mm2. Pawl bar 22 long, 10 wide, 8-14 thick.\n2) Ramp torque: T = F*r_m*(tan a + mu)/(1 - mu*tan a) = F x 10 mm x 0.407 = 4.07 mm x F. For 200 N this is 0.81 N*m, ~33 N at 25 mm. With mu = 0.2 the factor is 0.30, and 200 N needs 0.60 N*m (24 N).\n3) Ramp bearing, load normal to layers (housing printed with its axis vertical): 144 mm2 x 6 MPa = 860 N. Not limiting.\n4) Printed pawl, three-point bending (F = 4*sigma*Z/L, L = 16 mm). A 10 x 8 mm bar with a 5.3 mm hole: Z = (10-5.3) x 64/6 = 50 mm3. At 3 MPa that is only 37 N. At 14 mm thick, Z = 153 mm3 and F = 115 N. Hence a printed pawl alone gives ~100-150 N sustained.\n5) With a steel pawl (2-3 mm 304 stainless bar or plate, or a stainless T-head bolt), the limit moves to the frame ledge. Ledge shear across layers, 1.5V/A <= 2 MPa: A >= 1.5 x 200/2 = 150 mm2 for 200 N and ~260 mm2 for 350 N.\n6) Result: sustained 100 (printed pawl) / 200 (steel pawl, 150 mm2 printed ledge) / 350 N (steel pawl, steel keeper or insert boss). Peak ~700 N (range 500-1000): the ledge or pawl fails first.\n7) Commercial anchors, static and foam-gasket based: Essentra zinc quarter-turn compression lock 562 N max load at 6 mm compression, -50 to +80 C (from brief via search text). EMKA 1000-U805: 6 mm compression, IP65, PUR foam gasket, zinc body, no force rating on the page (verified). Second turn adds ~5.5 mm after a 3 mm ramp (verified). Southco E9 ~4 mm, IP66/IP67 (from brief; my fetch returned 403). These foam gaskets need roughly 0.2-1.4 N/mm, against 2-4 N/mm for the 85A design rib.\n8) Tolerance: a stroke-controlled ramp that ends at a fixed stop gives force proportional to stack-up error. +/-0.2 mm FDM tolerance on a 0.48 mm squeeze means roughly +/-40 % force. A nut on the shaft plus a wave spring would fix it but needs a 2.5-3 mm ramp rise.\n9) Retention: fixed-travel gives ~33-48 % loss after 70 C set (same chain as vise-action); ramp creep adds. Cold: ~2x force at -30 C.", "operating_force_N": 33, "preload_retention": "Poor to fair as a fixed-travel latch: ~33-48 % loss after hot sun (gasket set 35-52 % plus ramp and pawl creep), unless a wave spring or disc stack is added under the shaft nut with a 2.5-3 mm ramp rise (then ~10-17 %). If the ramp is long and the cam parks mid-ramp, the force is friction-held and can back off. Add a detent.", "adjustable_preload": true, "positive_compression_stop": true, "scores": { "seal_suitability": 5, "outdoor_durability": 6, "printability": 6, "usability": 7 }, "best_materials": "ASA for the knob and housing. Use a steel or hardened stainless pawl or cam (a printed one is weak and the ramp wears). Avoid PETG and PETG-CF at 60-70 C. Avoid PA6-CF outdoors. UV-stabilised PC may give ~1.3-1.5x margin on printed parts (own judgement). Avoid unstabilised PP.", "hardware": "Flagged: not printed. A2/A4 stainless M5 shaft or stud, nut and washers (the nut sets the grip), a 304 stainless pawl or T-head, optional wave spring or Belleville stack, optional O-ring or boot for the shaft hole. Or buy the commercial EMKA, Southco or Essentra latch.", "design_guidelines": [ "Housing and ramp: print with the axis vertical so the ramp load is normal to layers. Use a ramp rise of 1.5 mm for a rigid shaft (2.5-3 mm if a spring stack is fitted), mean radius 10 mm, arc >= 12 mm, radial width >= 6 mm, contact >= 140 mm2.", "End the ramp in a flat dwell of about 15 degrees plus a 0.3 mm detent. Without it the cam parks mid-ramp and the force becomes arbitrary, and it can back-drive under vibration.", "Pawl: use a steel bar if possible. A printed pawl needs >= 14 mm thickness and is still only ~100-150 N. Print it flat so bending runs along layers, with the hole axis along Z.", "Frame ledge: root section >= 150 mm2 (about 12 x 12 mm) for 200 N, with a root fillet >= 3 mm, or use a steel keeper or insert boss.", "Panel cutout 22-24 mm. Seal the shaft or cutout with an O-ring or a flange gasket. The hole is a leak path, and the commercial latches are rated IP65/66 only with their own gasket.", "Knob: a 50 mm wing or T-bar gives ~33 N hand force at 200 N. A coin slot or small key will not manage it. Hex or D-flat drive to the shaft.", "Add a printed land stop beside each latch at 0.75-0.8x the free bead height. The ramp alone does not define the squeeze.", "Set the grip with the shaft nut using a force gauge at mid-temperature. Do not rely on FDM tolerance." ], "failure_modes": [ "The printed pawl cracks at the shaft hole, or the ledge shears across layers.", "Ramp wear and creep: the ramp flattens and the draw is lost.", "The cam parks mid-ramp and the force is arbitrary.", "The latch back-drives under vibration or when greased.", "Force varies +/-40 % from FDM stack-up error.", "Gasket set at 70 C takes 33-48 % of a fixed-travel preload.", "Cold: force doubles at -30 C and the knob can crack.", "Shaft or cutout leak.", "Dirt in the ramp raises the friction." ], "existing_designs": [ { "title": "EMKA 1000-U805 compression latch [COMMERCIAL, not printable]", "url": "https://www.emka.com/products/1000-u805", "note": "Verified by fetch: 6 mm compression, IP65, PUR foamed gasket, zinc body, no force data." }, { "title": "ElectronicSpecifier: EMKA compression latch article [COMMERCIAL reference]", "url": "https://www.electronicspecifier.com/?p=113370", "note": "Verified by fetch: 3 mm ramp on the first turn, ~5.5 mm further compression on the second, IP65." }, { "title": "Southco E9-A005F-02 [COMMERCIAL, not printable]", "url": "https://southco.com/en_gb_int/e9-a005f-02", "note": "~4 mm compression, IP66/IP67 (from brief). My fetch returned 403." } ], "sources": [ { "title": "EMKA 1000-U805 compression latch", "url": "https://www.emka.com/products/1000-u805", "note": "Verified by fetch. 6 mm compression, IP65, PUR foam, no force rating." }, { "title": "ElectronicSpecifier: EMKA compression latch", "url": "https://www.electronicspecifier.com/?p=113370", "note": "Verified by fetch. 3 mm ramp, then 5.5 mm compression." }, { "title": "Essentra compression cam latch datasheet (DigiKey)", "url": "https://www.digikey.cn/htmldatasheets/production/2905106/0/0/1/compression-cam-latch-datasheet.pdf", "note": "From brief via search text, not re-fetched. 562 N at 6 mm, -50 to +80 C." }, { "title": "Southco E9-A005F-02", "url": "https://southco.com/en_gb_int/e9-a005f-02", "note": "From brief; fetch returned 403." }, { "title": "CNC Kitchen: comparing PLA, PETG and ASA (Prusament)", "url": "https://www.cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament", "note": "Verified by fetch. ASA hook lying 57 kg vs standing 17 kg. Used for the ledge anchor." }, { "title": "CNC Kitchen: helicoils, threaded inserts and embedded nuts (PETG M3)", "url": "https://www.cnckitchen.com/blog/helicoils-threaded-insets-and-embedded-nuts-in-3d-prints-strength-amp-strength-assessment", "note": "Verified by fetch. Insert in Z pull-out 119 kg." }, { "title": "Texin 985 datasheet", "url": "https://sushengpolymer.com/media/pdf/phFiH7_Texin-985.pdf", "note": "From brief, not re-fetched. Compression set and cold modulus." } ], "review": { "id": "quarter-turn-compression", "verdict": "corrected", "peak_clamp_force_N": 500, "sustained_clamp_force_N": { "low": 60, "typical": 150, "high": 300 }, "scores": { "seal_suitability": 5, "outdoor_durability": 5, "printability": 6, "usability": 7 }, "issues": [ "Sustained 200 N typical is optimistic. The printed-pawl case (100-150 N: a 10 x 14 mm pawl with a 5.3 mm hole, Z = 153 mm3, F = 4*3*153/16 = 115 N) is right. The 'steel pawl' tier then moves the limit to a printed ledge, which the analyst checks only in shear (150 mm2 gives 200 N). Root bending across layers (b=15, t=12, a=3-6 mm, 2 MPa) gives 120-240 N. Typical 150 N, and the 200-350 N tier needs a custom steel pawl plus a steel keeper or insert boss. A thin printed pawl (8 mm) gives 40 N, hence a low of 60 N.", "Operating force is understated. 4.07 mm x F (tan(alpha)=0.0955, 5.5 deg, MA 26 frictionless, 6:1 real) counts only the ramp. With a second sliding surface (about 1.8 mm x F), 150 N needs about 0.9 N*m, i.e. about 35 N on a 25 mm wing arm. 200 N would need 47 N, at the top of the 20-50 N comfort band.", "Peak 700 N is cut to 500 N. Printed ledge failure across layers is about 540 N at a=6 mm (9 MPa, the 29 % rule) and a printed pawl breaks lower. A zinc Southco N4 is rated 1200 N ultimate and a stainless M1 long cam 350 N static, so 700 N for a printed ASA copy is too close.", "The stroke is the wrong size. Commercial 4-6 mm travel against foam is replaced by a 1.5 mm printed ramp, and a ramp ending in a hard stop gives about +/-40 % force from the +/-0.2 mm FDM stack-up against a 0.48 mm squeeze. Without a detent the cam parks mid-ramp and the force is arbitrary. The latch also loses 33-74 % in hot sun (the analyst used 33-48 %).", "At 150 N each, the latch needs 19 units for 2.8 kN and 10 units for the 1.4 kN low window. It cannot fit a 70 mm body at those pitches, so it does not meet the reference requirement at 4-8 latches. Seal 5 stands. Durability 5: cam wear, a shaft hole that is a leak path, and a printed knob that cracks in the cold.", "Commercial anchors: EMKA 1000-U805 confirmed (6 mm compression, IP65, PUR foam, zinc die-cast, no force rating). ElectronicSpecifier confirmed 3 mm ramp then +5.5 mm and IP65, but dated 2011 and inconsistent with the EMKA page's 6 mm total. The Essentra 562 N / 6 mm / -50 to +80 C datasheet link on DigiKey is dead (HTTP 410), so that anchor is unverified. Southco E9 (IP66/IP67) returned 403." ], "confidence": "low", "reviewer_notes": "Independent recalculation. Ramp: arc = pi/2 x 10 = 15.7 mm, tan(alpha)=0.0955, T = F*10*(0.0955+0.3)/(1-0.02865) = 4.07 mm x F, checked. At 200 N: 0.81 N*m, 33 N at 25 mm, checked (24 N at mu=0.2). Printed pawl 10 x 8 mm: Z = 50 mm3, 37 N at 3 MPa; 10 x 14: Z = 153 mm3, 115 N. Ramp bearing 144 mm2 x 6 MPa = 860 N, not limiting, checked. The claim that foam gaskets need 0.2-1.4 N/mm against 2-4 N/mm for the 85A rib is plausible and unsourced; it explains why a latch rated for foam is poorly matched here. Commercial reference points verified: Southco N4 (600 N working, 1200 N ultimate, 300 N hand-turned compression force), M1 stainless long cam 350 N and short cam 1010 N max static. No printed quarter-turn test exists in the sources I could open. All values are estimates. This is the weakest of the four for the stated purpose (high sustained clamp on a TPU 85A gasket); its best role is as a convenient fastener on a soft low-load foam or thin-rib gasket.", "dead_or_misquoted_sources": [ "https://www.digikey.cn/htmldatasheets/production/2905106/0/0/1/compression-cam-latch-datasheet.pdf : HTTP 410 Gone, the 562 N Essentra claim cannot be verified", "https://southco.com/en_gb_int/e9-a005f-02 : HTTP 403, E9 4 mm and IP66/IP67 unverified", "https://www.electronicspecifier.com/?p=113370 : dated 2011; 3 mm ramp plus 5.5 mm second turn does not match the EMKA page's 6 mm total compression", "https://www.emka.com/products/1000-u805 : confirmed, but gives no force rating" ] } }, { "id": "threaded-lid-cap", "name": "Threaded closure (printed screw cap or threaded ring) with end-face TPU ring", "working_principle": "A coarse 30-degree trapezoidal (or buttress) thread on a round cap converts hand torque into axial force on a TPU 85A ring held on the end face; the thread is self-locking (lead angle about 1.6 deg versus a friction angle of 8-14 deg) so the cap holds without a detent, and it is a single closure (no latch pitch problem, force is spread evenly round the circle). The seal must be on the end face because a thread alone has a helical leak path. Force is set by hand torque, not by the thread strength: friction in the thread and, above all, the TPU ring scrubbing on its mating face eat most of the torque.", "mechanical_advantage": "Ideal (frictionless) T/F = lead/2pi = 0.64 mm for a 4 mm lead, i.e. an ideal ratio of about 63:1 at a 40 mm wing lever. With thread friction mu 0.25 the real T/F is 6.6 mm (ratio about 6:1; efficiency about 10 percent); mu 0.15 gives 4.2 mm. Adding TPU end-face drag (mu_c 0.5 at r_c 23 mm = 11.5 mm) gives T/F about 18 mm, a ratio of about 2:1. (all own calc, formula from https://en.wikipedia.org/wiki/Leadscrew)", "peak_clamp_force_N": 1800, "sustained_clamp_force_N": { "low": 100, "typical": 180, "high": 450 }, "limiting_factor": "In practice the achievable closing force is limited by hand torque (2-4 Nm) divided by thread plus TPU-face friction (T/F 6.5-26 mm), not by the printed thread, which can sustain more than 1 kN for a 50 mm cap with 3 engaged turns. The 1.8 kN peak is a structural estimate (thread/skirt delamination across layers); the force a hand can actually put on it is only about 600-700 N at best.", "force_basis": "calculated", "calculation": "ASSUMED PART (own): 50 mm major diameter, 30 deg trapezoidal thread, depth 2.0 mm, mean diameter d_m 46 mm, lead = pitch 4 mm (single start), 3 engaged turns (12 mm), skirt wall 4 mm, ASA, 5 perimeters, 0.2 mm layers, axis vertical (worst layer orientation). Lead angle = atan(4/(pi*46)) = 1.59 deg; flank half-angle 15 deg.\n1) Torque to axial force (formula from https://en.wikipedia.org/wiki/Leadscrew, own arithmetic): T = F (d_m/2) (mu sec(a) + tan(l)) / (1 - mu sec(a) tan(l)). Friction values plastic/plastic 0.25, plastic/steel 0.15 (https://elesa.com/en/elesab2bstoreca/Clamping-handles--Cam-levers--GN9272-A--d1). T/F = 6.6 mm at mu 0.25 and 4.2 mm at mu 0.15; frictionless T/F is 0.64 mm, so the thread is only about 10 percent efficient. Self-locking margin is large (mu sec(a) = 0.26 versus tan(l) = 0.028).\n2) TPU end-face drag (own; mu_c is NOT sourced, assumed 0.3-0.8 for TPU 85A on ASA, 0.1 with a PE/PTFE slip washer): the cap rotates on the TPU ring at r_c about 23 mm, adding 7-18 mm to T/F (2.3 mm with a slip washer). This term is missing from the simple thread-only torque numbers and it dominates.\n3) Hand torque 2-4 Nm (two-wing cap, about 40 mm lever x 50-100 N). Axial force at 3 Nm: best case (thread mu 0.15 + slip washer) 460 N; thread only (no scrub) 452 N; typical (mu_t 0.25, mu_c 0.5) 165 N; worst (0.30 / 0.8) 114 N. At 2 Nm and 4 Nm scale by 0.67 and 1.33. Delivered force therefore spans about 75-610 N, typically 110-220 N.\n4) Structural check (own plus measured anchor): flank projected bearing area = pi*46*2.0*3 = 867 mm2; across-layer sustained allowable about 2 MPa (project brief) gives about 1.7 kN. Skirt tension area about 680 mm2 gives about 1.4 kN. Measured anchor: PETG 1/2-20 threads printed vertically failed at about 80 lbf (about 356 N) per engaged turn, by a roughly 20 deg cone through the outer wall (https://3dprintingspace.com/t/thread-strength-testing/7351), i.e. about 8.9 N per mm of circumference per turn; scaled to 3 turns x pi x 46 mm = about 3.9 kN in PETG; x 0.68 for ASA versus PETG in standing-hook tests (17 vs 25 kg, https://cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament) = about 2.6 kN; I take 1.8 kN as peak after a roughly 30 percent haircut for untested scale-up and stair-stepped flanks. So the thread is not the limit below about 0.5 kN.\n5) Result: sustained low/typical/high = 100 / 180 / 450 N (2 Nm with heavy TPU drag / 3.3 Nm typical / best-friction case); peak 1800 N structural. On the 157 mm end-face ring that is 0.6 / 1.1 / 2.9 N/mm against the 2-4 N/mm design window, so only the best-friction case reaches it. Line load per unit torque scales roughly as 1/d^2: a 40 mm cap does about 1.6x better, a 70 mm cap about 2x worse at the same hand torque. Evidence caveat: further web searches were blocked (search budget exhausted); the above rests on direct page fetches only, and no test of a printed ASA cap with a TPU ring was found.", "operating_force_N": 85, "preload_retention": "Fair to poor. On a hard shoulder the cap is a rigid fixed-travel closure and loses roughly 30-58 percent of force when 85A TPU sets in hot sun (Ultrafuse 85A set 52 percent at 70 C, https://www.dream3d.co.uk/wp-content/uploads/2022/12/Ultrafuse_TPU_85A_TDS_EN_v2.5.pdf). Without a shoulder the cap can simply be re-tightened, which recovers the loss. ASA thread flanks also relax under sustained hot load, and vibration or thermal cycling can back the cap off despite the static self-lock. A series spring (wave washer or steel spring ring under the TPU) would cut the loss to about 10 percent (own calc, method from the project brief).", "adjustable_preload": true, "positive_compression_stop": true, "scores": { "seal_suitability": 5, "outdoor_durability": 7, "printability": 6, "usability": 7 }, "best_materials": "ASA (default; UV stable, HDT about 100 C). UV-stabilised PC could raise structural margins about 1.3-1.5x (own judgement, unmeasured) but does not raise the hand-torque-limited force. Avoid PETG and PETG-CF (HDT 68 C is at the sun-heated surface temperature), avoid PA6-CF (3.3 percent water uptake). PAHT-CF acceptable but creeps.", "hardware": "None required (fully printed). Optional but recommended: PE or PTFE slip washer (or grease) between the TPU ring and the rotating face to cut end-face drag; A2/A4 stainless spring plunger or printed pawl as a lock; a wave washer as a series spring. A rubber O-ring in a radial gland is a better seal than a printed TPU ring, because the thread then carries no sealing load.", "design_guidelines": [ "Thread: 30 deg trapezoidal or buttress, pitch 4-5 mm, depth 1.6-2.0 mm, 0.3-0.4 mm flank clearance for FDM, at least 3 (preferably 4) engaged turns, plus a 3-5 mm cylindrical pilot spigot so the cap cannot cock and squeeze the gasket unevenly.", "Skirt wall at least 4 mm outside the thread root, 5+ perimeters, 0.16-0.2 mm layers; thread axis vertical keeps the sealing faces flat, but if the part allows, a horizontal or 45 deg axis is stronger (45 deg was strongest for ASA nuts, https://www.mmscience.eu/journal/issues/june-2025/articles/analysis-of-3d-printed-metric-nuts-manufactured-by-the-mex-method-from-asa-material).", "Seal on the end face with a narrow rib (1.2-1.6 mm wide, at least 2 mm tall) rather than a wide bead, and keep the TPU ring on the non-rotating part; place a PE/PTFE slip washer or a polished, ironed land on the rotating face.", "Add a hard shoulder so the cap bottoms at about 0.75-0.8 x free rib height of squeeze; accept that a shoulder removes re-tightening, or leave 0.5 mm of adjustable gap and use a lock.", "Give the cap wings or a lever of at least 35-40 mm radius; do not rely on a 25 mm knurled rim (it needs about 130 N tangential force for the typical load).", "Add a lock against unscrewing: a flex-tooth ratchet or an A4 spring plunger in a 2-3 mm detent.", "Size the cap so the required line load is met: force needed = 2-4 N/mm x circumference, e.g. 314-628 N for a 50 mm cap; above about 50 mm diameter hand torque is not enough.", "Round fillets (R at least 1 mm) at thread runouts and the skirt to cap transition; no sharp internal corners (ASA is only about 3 kJ/m2 notched Charpy at -30 C, per the brief)." ], "failure_modes": [ "TPU ring scrubbing and twisting during closing: rib rolls, tears (printed TPU 85A edge-on tear only 18-30 kN/m) or wears, and friction eats 60-75 percent of the torque.", "Thread-root or skirt delamination across layers in hot sun when over-tightened (vertical print).", "Cross-threading or cocking, giving uneven squeeze and a leak path on one side.", "Loss of preload from TPU compression set and thread-flank creep (52 percent set at 70 C).", "Cap backing off with vibration or thermal cycling; or seizing from dirt, ice or sun-softened threads.", "Brittle cracking of the skirt in cold if there are sharp corners.", "Helical leak path if the seal is placed on the thread instead of the end face." ], "existing_designs": [ { "title": "Container: sealable, screwable, scaleable, strong (Printables)", "url": "https://printables.com/model/1233019-container-sealable-screwable-scaleable-strong-3-ve", "note": "Screw container with a TPU 95A seal per the lead; returned HTTP 403 to my fetch so not re-verified; no force data" } ], "sources": [ { "title": "3D Printing Space: thread strength testing", "url": "https://3dprintingspace.com/t/thread-strength-testing/7351", "note": "Fetched and verified: PETG 1/2-20 vertical threads about 80 lbf per engaged turn, about 20 deg cone failure through the outer wall; PLA about 150 lbf per turn; forum test, not a lab study" }, { "title": "Hackaday: putting 3D printed screw threads to the test", "url": "https://hackaday.com/2023/11/10/putting-3d-printed-screw-threads-to-the-test", "note": "Fetched: article is qualitative (bottom layers peel); the 48 / 68 / 90 / over 110 lbf by infill figures for 1/4-20 PLA+ are from a reader comment, not the article" }, { "title": "MM Science: 3D printed metric nuts in ASA (abstract)", "url": "https://www.mmscience.eu/journal/issues/june-2025/articles/analysis-of-3d-printed-metric-nuts-manufactured-by-the-mex-method-from-asa-material", "note": "Fetched abstract: 45 deg build orientation gave highest tensile strength; formed threads unsatisfactory; best nut over 14.7 MPa; no newton values" }, { "title": "Hackaday.io: printed cap splits along layers under bolt force", "url": "https://hackaday.io/project/12125/log/41900", "note": "Fetched: PLA part split along layers under bolt and washer force; no numbers" }, { "title": "Wikipedia: Leadscrew", "url": "https://en.wikipedia.org/wiki/Leadscrew", "note": "Fetched: torque and efficiency formulas for Acme-type threads and self-locking condition" }, { "title": "Elesa GN 927.2 page (friction coefficients)", "url": "https://elesa.com/en/elesab2bstoreca/Clamping-handles--Cam-levers--GN9272-A--d1", "note": "Fetched: plastic/plastic 0.25, plastic/steel 0.15" }, { "title": "PMC9781732: compression of FDM PLA threaded rods", "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC9781732/", "note": "Fetched: this paper is about PLA rods in compression; its under-30-percent clamping-force remark is a cited M12 SLA-resin bolt result, NOT FDM evidence, so it should not be used for printed-thread claims" }, { "title": "CNC Kitchen: comparing PLA, PETG and ASA (Prusament)", "url": "https://cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament", "note": "Standing-vs-lying hook figures taken from the project brief, not re-fetched" }, { "title": "Ultrafuse TPU 85A datasheet", "url": "https://www.dream3d.co.uk/wp-content/uploads/2022/12/Ultrafuse_TPU_85A_TDS_EN_v2.5.pdf", "note": "Compression set 26 percent at 23 C and 52 percent at 70 C, tear anisotropy; figures from the project brief, not re-checked" } ], "review": { "id": "threaded-lid-cap", "verdict": "corrected", "peak_clamp_force_N": 1400, "sustained_clamp_force_N": { "low": 90, "typical": 165, "high": 400 }, "scores": { "seal_suitability": 4, "outdoor_durability": 7, "printability": 6, "usability": 6 }, "issues": [ "Torque-to-force arithmetic is right (recomputed T/F: 6.64 mm at mu 0.25, 4.23 mm at 0.15; frictionless 0.64 mm). With TPU end-face drag at mu_c 0.5 and r_c 23 mm, 3 Nm gives 165 N (analyst: 165-180). Using d_m 48 mm, which is what a 50 mm major diameter with 2 mm depth gives, changes this by only about 2 percent.", "The dominant term, TPU 85A on ASA friction mu_c, is unsourced. My search budget was exhausted, so I could not source it. Dry 85A TPU on smooth plastic is plausibly 0.6-1.0, not 0.5. At mu_c 0.8 the force is 120 N, and at mu_t 0.35 (layer-lined FDM thread rather than injection-moulded plastic) it is about 145 N. So typical is trimmed from 180 to 165 N and low from 100 to 90 N. The sustained figure is torque-limited, not strength-limited.", "The claim that the printed thread can sustain more than 1 kN is refuted. It rested on flank bearing area (867 mm2 x 2 MPa), which is not the failure mode. Tooth-root bending across layers is. For a 4 mm pitch tooth (root about 2.4-2.5 mm, depth 2 mm, load at mid-depth) the nominal root stress is about 1.0 MPa at 450 N over 3 uniformly loaded turns. With Kt 2-2.5 that is 2.1-2.6 MPa, already at or above the 2 MPa across-layer sustained allowable. The real structural sustained ceiling is about 380-480 N, and less with the usual first-turn load concentration. So the 450 N high case is capped at 400 N. It also needs grease plus a slip washer plus about 3 Nm, which is 37 N per finger on 40 mm wings.", "The 1.8 kN peak extrapolates a 1/2-20 PETG fine-thread forum test (80 lbf per turn, about 20 deg cone, confirmed on the page) to a 50 mm coarse ASA thread. My own check is 12.7 MPa (29 percent of Polymaker's 43.8 MPa XY) divided by Kt 2-2.5 and spread over 3 turns. That gives 2.2-2.8 kN with perfectly uniform load, but only about 1.8-2.3 kN if the first turn carries about 40 percent. With the room-temperature data flattered (see the Polymaker note below), I take 1.4 kN. Peak is not deliverable by hand: 1.4 kN at T/F 18 mm is about 25 Nm.", "The hand-torque input is borderline. 2-4 Nm needs a two-wing couple of 25-50 N per finger on 40 mm arms, which is the top of the 20-50 N comfortable range. A single-point 50-100 N, as the lever arithmetic is written, is unrealistic. The 80 mm wing span and 50 mm diameter also exceed the 70 x 35 x 30 mm reference envelope, and it only suits round openings of about 50 mm or less.", "Scale limit: line load times circumference needs force that grows with diameter, and torque grows with diameter squared. A 100 mm cap at 2 N/mm needs about 628 N x 31 mm, roughly 19 Nm, which is not by hand. Seal suitability is therefore lowered from 5 to 4. The typical 0.6-1.1 N/mm is below the 2-4 N/mm window.", "Cold: at -20 C the 85A modulus is about 2x, so at a hard stop the closing torque rises 1.5-2x. Fixed-stop closure may be hand-limited short of the stop in winter. This is not addressed.", "The flank is 15 deg off horizontal, which is a roughly 75 deg overhang from vertical for the downward-facing flank. Printability stays at 6 but needs a note: use a buttress thread with a 45 deg trailing flank, or accept stair-stepped flanks.", "Usability is lowered from 7 to 6. Closing needs 3+ full turns, about 43 N per finger, scrubs a TPU ring, and has the cold-stiffening penalty above." ], "confidence": "medium", "reviewer_notes": "I recomputed everything from the formulas. Lead-screw T/F with the sec(alpha) term, taken from the Wikipedia Leadscrew page, gives 6.64 / 4.23 mm at mu 0.25 / 0.15. Adding TPU drag mu_c x r_c (0.5 x 23 = 11.5 mm), 3 Nm gives 165 N, which matches the analyst's typical of 180 within 10 percent. Sensitivity: mu_c 0.3 gives 222 N, 0.8 gives 120 N, and best case (grease plus slip washer, 3 Nm) gives 460 N (2.9 N/mm on the 157 mm ring). I checked the thread tooth as a cantilever in bending across layers (1.0 MPa at 450 N, before Kt). I also checked skirt tension (680 mm2 x 2 MPa = 1.36 kN, correct). The analyst's tooth and skirt checks use the wrong failure mode for the thread, and that is what I corrected. Verdict is corrected because the structural claim of more than 1 kN is wrong, even though the typical force lands within about 10 percent. Source checks: 3dprintingspace.com thread test is live and consistent (PETG 80 lbf per thread, 3 threads 240 lbf, about 20 deg cone, PLA about 150 lbf per thread). It is a 1/2-20 fine thread with a 14 mm ID recess, so scaling to 50 mm coarse ASA is an extrapolation. CNC Kitchen hook test confirmed (ASA 57 lying / 17 standing kg, PETG 55/25). Ultrafuse TDS extracted locally: compression set 26 percent at 23 C/72 h and 52 percent at 70 C/24 h (ISO 815), tear 80/18/30 kN/m, break stress 34 vs 10 MPa. All match. Elesa friction values (0.25 plastic/plastic, 0.15 plastic/steel) confirmed. MM Science abstract confirmed (45 deg highest strength, formed threads unsatisfactory, M10 nut above 14.7 MPa). The Polymaker ASA TDS was read locally: XY 43.8, Z 32 MPa, Z elongation 1.65 percent, HDT 100.2 C, Tg 97.8 C. Its specimens were printed with a 70 C chamber and 100 percent infill and the sheet says not to use them for design, so the 73 percent Z/XY ratio overstates real parts. I did not find any source for printed-thread torque-to-clamp performance; no test of an ASA cap with a TPU ring exists in what was available.", "dead_or_misquoted_sources": [ "https://printables.com/model/1233019-container-sealable-screwable-scaleable-strong-3-ve - HTTP 403 for me too; the TPU 95A seal claim is unverified and there is no force data.", "https://3dprintingspace.com/t/thread-strength-testing/7351 - live and accurate, but a fine-pitch PETG test (80 lbf per turn) extrapolated to a coarse 50 mm ASA thread; the PLA 2-thread figure on the page is internally inconsistent (300 vs 204 lbf).", "https://hackaday.com/2023/11/10/putting-3d-printed-screw-threads-to-the-test - the lbf figures are one reader comment (1/4-20, PLA+ per the article), not the article. The analyst already flagged this.", "https://pmc.ncbi.nlm.nih.gov/articles/PMC9781732/ - PLA M42-M64 rods in compression; the under-30-percent clamping remark is a cited study by Wi et al. I could not confirm the analyst's 'M12 SLA resin' detail. Not usable for FDM thread claims, as the analyst said.", "https://cdn.shopify.com/s/files/1/0603/6609/files/PolyLite_ASA_TDS_V5.1.pdf - figures confirmed, but the specimens were printed in a 70 C chamber at 100 percent infill and the sheet says not to design from them." ] } }, { "id": "bayonet-twist-lock", "name": "Bayonet / twist-lock lid with ramps", "working_principle": "Radial lugs on the lid slide under helical ramps (retaining ledges) on the body; rotating the lid 30-45 degrees climbs the ramps and pulls the lid axially onto the gasket, ending in a flat dwell with a detent. A shallow ramp (3-8 deg) is self-locking against the gasket spring-back (tan 5 deg = 0.09 versus friction 0.15-0.25), but vibration can still rotate it back, so a detent is needed. The whole lid is one closure with no latch count, but force is limited by hand torque, TPU ring scrubbing during rotation, and the lug roots, which are loaded across layers when the axis is vertical.", "mechanical_advantage": "Ramp: F = T / (r tan(alpha + phi)). For r = 27 mm and a 5 deg ramp the frictionless T/F is r tan(alpha) = 2.4 mm (ideal ratio about 15:1 at a 35 mm wing lever); with ramp friction mu 0.25 it is 9.3 mm (mu 0.15: 6.5 mm); adding TPU drag (mu_c 0.5 at r_c 25 mm = 12.5 mm) gives about 22 mm, i.e. an effective ratio of only about 1.6:1 at the wing. Steeper ramps give less force per torque. (all own calc)", "peak_clamp_force_N": 700, "sustained_clamp_force_N": { "low": 50, "typical": 120, "high": 200 }, "limiting_factor": "Hand torque divided by ramp friction plus TPU-ring drag (about 95-180 N typical at 2-4 Nm), and the lug roots in bending across layers (about 180-270 N sustained for 16 x 3 x 5 mm lugs, with only two of three lugs bearing in practice).", "force_basis": "calculated", "calculation": "ASSUMED PART (own): 56 mm OD lid, 3 lugs at 120 deg, each 16 mm arc x 3 mm radial x 5 mm thick; ramp contact radius r = 27 mm, ramp 5 deg, about 40 deg of rotation including a 4 mm dwell with detent; ASA; lid printed sealing-face down, axis vertical.\n1) Torque to axial force: F = T / [r tan(alpha + phi) + mu_c r_c] (ramp formula as in the lead's evidence, with TPU drag added by me). Friction 0.25 plastic/plastic, 0.15 plastic/steel (https://elesa.com/en/elesab2bstoreca/Clamping-handles--Cam-levers--GN9272-A--d1). r tan(alpha+phi) = 9.3 mm (mu 0.25), 6.5 mm (mu 0.15); frictionless 2.4 mm. TPU drag (mu_c NOT sourced, assumed 0.5; 0.8 worst; 0.1 with a slip washer) at r_c 25 mm adds 12.5 mm (20 mm worst, 2.5 mm best). At 2 / 3 / 4 Nm: ramp-only 215 / 322 / 430 N; typical with TPU drag (T/F 21.8 mm) 92 / 138 / 183 N; best case (mu 0.15 + slip washer) 222 / 333 / 444 N; worst case at 2 Nm about 70 N.\n2) Lugs (own beam calc). Each lug carries P = F/3 at an arm l = 1.5 mm; the root bending stress acts along the axis, i.e. across layers for a vertical print: sigma = 6 P l / (b h^2) = 6 x 1.5 x P / (16 x 25) = 0.0225 MPa per N. Sustained across-layer allowable about 2 MPa (project brief) gives P = 89 N, F = 267 N for three lugs, about 180 N when tolerances leave only two lugs bearing. Peak: roughly 12 MPa across layers at room temperature (ASA standing hooks reach only 29 percent of lying, https://cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament) divided by Kt 1.5 gives P = 355 N, F about 1070 N, x 2/3 = about 710 N. Lug shear and bearing (P/(16 x 5) and P/(16 x 3)) stay near 1-2 MPa, well below limits.\n3) Result: sustained low / typical / high = 50 / 120 / 200 N (2 Nm with heavy drag / 2.6 Nm typical case / lug limit); peak 700 N. On the 170 mm lug circle the typical value is about 0.7 N/mm, far below the 2-4 N/mm window; a lid reaches 2 N/mm only if its circumference is under about 60 mm (diameter about 20 mm). Nothing in the lead's evidence conflicts: no pull-off or torque tests exist for printed bayonets (maker and industrial estimates 50-300 N), so this remains a low-confidence calculation. Further web searches were blocked (search budget exhausted); MakerWorld pages returned HTTP 403.", "operating_force_N": 75, "preload_retention": "Poor. The ramp is a rigid fixed-travel element, so about 30-58 percent of force is lost when 85A TPU takes a set at 70 C (Ultrafuse 85A set 52 percent at 70 C, https://www.dream3d.co.uk/wp-content/uploads/2022/12/Ultrafuse_TPU_85A_TDS_EN_v2.5.pdf), and ASA ramps and lugs creep further. The preload is fixed by the ramp dwell height and cannot be re-tightened without shims; a steel wave spring under the TPU or a flexible ramp would be needed.", "adjustable_preload": false, "positive_compression_stop": true, "scores": { "seal_suitability": 4, "outdoor_durability": 5, "printability": 5, "usability": 8 }, "best_materials": "ASA for the lid and body ledges. PC (UV-stabilised) raises lug and creep margin about 1.3-1.5x (own judgement) but not the hand-torque limit. PETG is marginal at 60-70 C. PA6-CF not recommended outdoors (moisture). A metal ramp insert or stainless detent pin helps wear.", "hardware": "None required. Optional: A4 stainless spring plunger or ball detent (M4) for the dwell, PE/PTFE slip washer under the TPU ring, A4 pins as lugs if the printed lugs are the limit.", "design_guidelines": [ "Use 3 lugs at 120 deg, each at least 16 mm of arc, 3 mm radial, 5-6 mm thick, with R at least 1.5 mm fillets at the root (root bending across layers is the weak spot for a vertical print).", "Ramp 4-6 deg (self-locking) with a 3-5 mm flat dwell plus a 0.3-0.4 mm detent bump and a hard rotation stop; the ramp end height should set the squeeze at about 0.75-0.8 x free rib height.", "Print the body open-end-down on the bed so the ramp bearing faces sit at the bed and need no bridging or support; print the lid sealing-face down.", "Wings or a lever at least 35 mm radius so 2.5-3 Nm needs under 80 N finger force.", "Keep the TPU rib narrow (1.2-1.6 mm) and put it on the non-rotating part; use an ironed land or slip washer on the rotating face to cut drag.", "Apply a second print-quality check on the three ramps: all three must bear equally, so tune with 0.1 mm shims or print the ledges as separate adjustable pads.", "Rated use: small round lids up to about 20-30 mm for a 2-4 N/mm gasket; larger lids need a different latch.", "Include a visual lock-position mark and a finger lead-in chamfer so the lugs enter the entry slots without cocking." ], "failure_modes": [ "Lug root delamination across layers; one of three lugs overloaded by tolerances.", "Ramp and dwell creep or wear, so the lid loosens over months in sun.", "Lid unwinds with vibration if no detent or if the detent creeps.", "TPU ring scrubbing and rolling during rotation; an under-extruded sealing face leaks.", "Overhanging ramp sagging or stringing in print, giving uneven squeeze.", "Dirt, ice or sand packed in the slots jams the lugs.", "Force too low (about 0.7 N/mm typical) so the gasket leaks on lids larger than about 20 mm." ], "existing_designs": [ { "title": "MakerWorld heavy-duty two-lug bayonet lid", "url": "https://makerworld.com/models/1924555", "note": "PETG, printed upside-down, designer reports months outdoors (via lead search text); HTTP 403 to my fetch, no force data" }, { "title": "Customizable Waterproof Pill Box (stlfinder)", "url": "https://www.stlfinder.com/model/customizable-waterproof-pill-box-FhdEExnI/2424312", "note": "About 1/8-turn bayonet; claims 10 cm for 10 min; HTTP 403 to my fetch, so claim not re-verified" } ], "sources": [ { "title": "Wikipedia: Bayonet mount", "url": "https://en.wikipedia.org/wiki/Bayonet_mount", "note": "Principle (pegs, slots, detent or spring) and failure modes; fetched by the lead, not by me" }, { "title": "Elesa GN 927.2 page (friction coefficients)", "url": "https://elesa.com/en/elesab2bstoreca/Clamping-handles--Cam-levers--GN9272-A--d1", "note": "Fetched: plastic/plastic 0.25, plastic/steel 0.15" }, { "title": "CNC Kitchen: comparing PLA, PETG and ASA (Prusament)", "url": "https://cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament", "note": "Standing-vs-lying hook figures (ASA 17 vs 57 kg) taken from the project brief, not re-fetched" }, { "title": "Ultrafuse TPU 85A datasheet", "url": "https://www.dream3d.co.uk/wp-content/uploads/2022/12/Ultrafuse_TPU_85A_TDS_EN_v2.5.pdf", "note": "Compression set figures from the project brief, not re-checked" }, { "title": "Hackaday.io: printed cap splits along layers under bolt force", "url": "https://hackaday.io/project/12125/log/41900", "note": "Fetched: layer splitting of an as-printed PLA part under bolt force; supports the across-layers lug concern, no numbers" } ], "review": { "id": "bayonet-twist-lock", "verdict": "confirmed", "peak_clamp_force_N": 600, "sustained_clamp_force_N": { "low": 50, "typical": 120, "high": 180 }, "scores": { "seal_suitability": 3, "outdoor_durability": 5, "printability": 5, "usability": 7 }, "issues": [ "Ramp arithmetic confirmed: r tan(alpha+phi) = 9.3 mm (mu 0.25), 6.5 mm (mu 0.15); plus TPU drag 12.5 mm gives 92 / 138 / 183 N at 2 / 3 / 4 Nm. The typical 120 N at about 2.6 Nm reproduces. As with the cap, the TPU-on-ASA mu_c of 0.5 is unsourced. mu_c 0.8 gives 68 N at 2 Nm, and mu_ramp 0.35 gives about 100 N at 2.5 Nm.", "The lug limit was computed without a stress concentration. The root stress is 0.0225 MPa per N (recomputed), so 2 MPa across layers gives 267 N for three lugs. With Kt 1.5 it is 178 N for three lugs and 119 N when tolerances leave two lugs bearing. So the lug ceiling and the hand-torque result nearly coincide at 120-180 N, and the high case is trimmed from 200 to 180 N.", "Peak of 700 N relied on Kt 1.5. With a more realistic printed-fillet Kt of 2 it is about 565 N (Kt 1.5 gives 750 N). Lowered to 600 N. Peak is not hand-deliverable: 600 N at 22 mm T/F is about 13 Nm.", "The mating ledge on the body is an equal cantilever loaded across layers when the axis is vertical, and was not checked. Typically it has a longer arc and is stronger than the lugs, but it is a second weak point.", "Cold, fixed stroke: the 85A modulus at -20 C is about 2x, so the dwell force would be 180-240 N (above the lug sustained limit), and the lid may not reach the dwell at 3 Nm. Hot: the 52 percent set at 70 C cuts force 30-58 percent and cannot be re-tightened. The sustained range is therefore wide (about 60-240 N over the year).", "At about 0.7 N/mm typical on a 170 mm lug circle (confirmed), it is far below the 1.7 N/mm Garlock-equivalent for a 1.2 mm rib and below the 2-4 N/mm window. Seal suitability is lowered from 4 to 3. Practical only for small round lids or thin foam/lip seals.", "Usability is lowered from 8 to 7. It is a quick 40 deg turn, but it needs a wing and 2.6 Nm (about 33 N per finger on 40 mm arms), a fussy three-lug alignment, and extra effort when cold. The conventional bayonet has a spring detent and no force data exists for printed lugs." ], "confidence": "low", "reviewer_notes": "I recomputed the ramp formula F = T / (r tan(alpha+phi) + mu_c r_c). The results are 92 / 138 / 183 N at 2 / 3 / 4 Nm for mu 0.25, mu_c 0.5, and 333 N at 3 Nm for the best case (mu 0.15, slip washer). The analyst's typical of 120 N is confirmed. The lug cantilever (16 x 3 x 5 mm, arm 1.5 mm) gives 0.0225 MPa per N, so 2 MPa gives 267 N (three lugs) or 178 N with Kt 1.5. The brief's across-layer allowable of 2 MPa is the key assumption and is unmeasured for ASA at 60-70 C. The peak uses 12.7 MPa (0.29 x 43.8 MPa Polymaker XY), which agrees with the CNC Kitchen 29 percent standing-hook ratio. Sources: Wikipedia Bayonet mount fetched and consistent (L-slot, spring-loaded detent, failure by peg or sleeve breakage, spring failure or vibration; it says bayonets resist vibration better than screw joints). Elesa friction confirmed. CNC Kitchen hook ratio confirmed. Ultrafuse set 26/52 percent confirmed. Hackaday.io log confirmed as qualitative only (PLA split along layers, no numbers). Both MakerWorld and stlfinder pages were HTTP 403 and could not be checked. Neither drives a force number. My search budget was exhausted, so I found no published pull-off or torque test for printed bayonets. The result is a calculation only, and I mark the confidence low. Verdict is confirmed because the typical lands within 5 percent and the sources that drive the force numbers check out; peak, high, scores trimmed.", "dead_or_misquoted_sources": [ "https://makerworld.com/models/1924555 - HTTP 403, 'months outdoors in PETG' claim unverifiable.", "https://www.stlfinder.com/model/customizable-waterproof-pill-box-FhdEExnI/2424312 - HTTP 403, '10 cm for 10 min' claim unverifiable.", "https://hackaday.io/project/12125/log/41900 - live, but PLA with no numbers; it supports only the qualitative across-layers concern." ] } }, { "id": "rotary-cam-lock-simple", "name": "Rotary cam lock / tapered quarter-turn latch with little or no draw-down", "working_principle": "A quarter-turn cam tongue (or tapered tongue) on a shaft turns behind the frame or panel; a plain tongue gives no defined compression, a roller or tapered cam draws the panel down by up to about 2 mm (Southco E5 roller cam). It is easy to print on a stainless shaft, but the force path is a thin cantilevered tongue in bending with a line contact, so it creeps and carries little load. Fine for dust or splash with foam or thin-lip gaskets, or as a secondary lock, not for a TPU 85A rib.", "mechanical_advantage": "Taper ramp: F = T / (r tan(alpha + phi)). For r = 12 mm and an 8 deg ramp, T/F = 4.9 mm at mu 0.25 and 3.6 mm at mu 0.15 (frictionless 1.7 mm). With an 18 mm thumb-knob radius the force ratio is about 3.7-5:1 (T handle at 40 mm radius about 8-11:1). A plain cam with no taper has effectively no draw-down. (own calc)", "peak_clamp_force_N": 250, "sustained_clamp_force_N": { "low": 25, "typical": 60, "high": 100 }, "limiting_factor": "The printed tongue in bending (about 0.05-0.2 MPa per newton depending on thickness; 3-6 MPa sustained allowable gives 25-100 N) and the hub/shaft bearing, not the hand: a thumb knob can easily deliver 165-225 N at 0.8 Nm and overload the tongue.", "force_basis": "estimated", "calculation": "ASSUMED PART (own): printed cam tongue 14 mm wide x 8 mm thick, contact 8 mm from the hub root and r = 12 mm from the shaft axis, 8 deg taper, on an M5 A4 stainless screw or D-shaft, thumb knob radius 18 mm (hand torque 0.5-1 Nm; up to 1.5 Nm with a T handle). Printed with the shaft axis horizontal so that in the lock position the tongue lies in the layer plane and bends in-plane.\n1) Torque to force: F = T / (r tan(alpha + phi)). Friction values 0.25 plastic/plastic and 0.15 plastic/steel (https://elesa.com/en/elesab2bstoreca/Clamping-handles--Cam-levers--GN9272-A--d1). r tan(alpha+phi) = 4.9 mm (mu 0.25), 3.6 mm (mu 0.15); frictionless 1.7 mm. At 0.8 Nm that is 165-225 N, so the hand can overload the tongue.\n2) Tongue as a cantilever (own): sigma = 6 F l / (b h^2) = 6 x 8 / (14 x 64) = 0.054 MPa per N. Sustained in-plane allowable 3 / 4 / 6 MPa (project brief rule for ASA at 60-70 C) x 0.85 root-fillet factor gives F = 48 / 64 / 95 N. A thinner 4-6 mm tongue (typical of printed cams) has 0.1-0.2 MPa per N, i.e. only 15-40 N. I therefore report sustained 25 / 60 / 100 N. Peak: in-plane XY tensile about 37-44 MPa for ASA datasheets (Polymaker https://cdn.shopify.com/s/files/1/0603/6609/files/PolyLite_ASA_TDS_V5.1.pdf) / Kt 1.5 gives about 20 MPa, so about 370 N for the 8 mm tongue; hand-limited at 1.5 Nm = 310 N; I report 250 N as a margin-adjusted peak.\n3) Context: a metal eccentric clamping lever (Elesa GN 927.2, size 44) gives 1450 N for 75 N hand force (https://elesa.com/en/elesab2bstoreca/Clamping-handles--Cam-levers--GN9272-A--d1), which shows how far a simple quarter-turn printed cam is from a true clamp; Southco E5 roller cam compresses up to 2 mm of light-duty gasket and its Flush Cup meets NEMA 4 / IP65 but no holding force is stated (https://brandspurng.com/2020/09/23/southco-introduces-new-product-extensions-to-its-successful-e5-cam-latch-series/). A stainless cam on the same shaft would carry several hundred N, but then it is not printed.\n4) Seal check: at 2-4 N/mm a 60 N cam can serve only about 15-30 mm of gasket, so a 200 x 150 mm lid would need 25-45 cams. Further web searches were blocked (search budget exhausted); the MakerWorld printed quarter-turn latch page returned HTTP 403, so no printed-cam force data was found.", "operating_force_N": 16, "preload_retention": "Poor. The cam is a rigid fixed-travel element on a thin printed tongue: TPU set (30-58 percent force loss at 70 C, https://www.dream3d.co.uk/wp-content/uploads/2022/12/Ultrafuse_TPU_85A_TDS_EN_v2.5.pdf) combines with tongue bending creep and line-contact wear, so little of the original preload survives hot summers. It cannot be re-tightened.", "adjustable_preload": false, "positive_compression_stop": false, "scores": { "seal_suitability": 2, "outdoor_durability": 5, "printability": 8, "usability": 7 }, "best_materials": "ASA for the cam and knob; PC (UV-stabilised) improves tongue creep margin about 1.3-1.5x (own judgement). A stainless or die-cast cam is the realistic way to more than about 100 N. Avoid PETG and PA6-CF outdoors.", "hardware": "M5 A4 stainless screw or D-shaft, A4 washer, A4 nyloc or lock nut; optional stainless cam or roller; optional spring plunger detent. A threaded stud with lock nut would make the cam height adjustable.", "design_guidelines": [ "Tongue at least 8 mm thick and 14 mm wide with R at least 3 mm fillet at the hub; reach no more than 12 mm from the shaft axis.", "Print with the shaft axis horizontal so that the tongue in the lock position lies in-plane, not across layers.", "Taper ramp 3-8 deg over the last 90 deg of rotation, with a rotation stop and a detent bump; a roller or low-friction face reduces wear.", "Metal shaft or stainless bush in the hub (A4 M5); never let the printed hole bear on the thread.", "Use only with a light gasket (thin lip or foam) or put one latch every 15-30 mm.", "Add a separate printed hard stop beside each latch, since the cam itself defines no squeeze.", "For loads over about 100 N substitute a stainless cam or use another mechanism." ], "failure_modes": [ "Tongue creeps or cracks at the hub fillet.", "Printed hole creeps around the steel shaft, so the cam drops and loses preload.", "Cam rotates back with vibration without a detent.", "Line contact wear; zinc-plated shafts rust within months outdoors (12-72 h salt spray).", "Gasket leaks because force is simply too low.", "Cold brittleness at sharp corners of the tongue." ], "existing_designs": [ { "title": "MakerWorld quarter-turn latch (compression capable)", "url": "https://makerworld.com/models/3070853", "note": "Four printed parts, 90 deg turn, taper compression, default for 2.5 mm acrylic panel; no force data (per lead; HTTP 403 to my fetch)" }, { "title": "Southco E5 cam latch extensions (metal reference)", "url": "https://brandspurng.com/2020/09/23/southco-introduces-new-product-extensions-to-its-successful-e5-cam-latch-series/", "note": "Roller cam up to 2 mm compression; Flush Cup accessory NEMA 4 / IP65; no holding force stated (fetched)" } ], "sources": [ { "title": "Southco E5 cam latch extensions", "url": "https://brandspurng.com/2020/09/23/southco-introduces-new-product-extensions-to-its-successful-e5-cam-latch-series/", "note": "Fetched: up to 2 mm light-duty compression, NEMA 4 / IP65 for the Flush Cup; no load rating given" }, { "title": "Elesa GN 927.2 page", "url": "https://elesa.com/en/elesab2bstoreca/Clamping-handles--Cam-levers--GN9272-A--d1", "note": "Fetched: friction coefficients (0.25 / 0.15) and metal cam-lever table (75 N hand gives 1450 N clamp for size 44)" }, { "title": "Polymaker PolyLite ASA datasheet", "url": "https://cdn.shopify.com/s/files/1/0603/6609/files/PolyLite_ASA_TDS_V5.1.pdf", "note": "ASA XY and Z tensile figures as given in the project brief, not re-fetched" }, { "title": "MakerWorld quarter-turn latch", "url": "https://makerworld.com/models/3070853", "note": "Not retrievable (HTTP 403); description via the lead's search summary" }, { "title": "Ultrafuse TPU 85A datasheet", "url": "https://www.dream3d.co.uk/wp-content/uploads/2022/12/Ultrafuse_TPU_85A_TDS_EN_v2.5.pdf", "note": "Compression set figures from the project brief, not re-checked" } ], "review": { "id": "rotary-cam-lock-simple", "verdict": "confirmed", "peak_clamp_force_N": 350, "sustained_clamp_force_N": { "low": 25, "typical": 60, "high": 100 }, "scores": { "seal_suitability": 2, "outdoor_durability": 5, "printability": 8, "usability": 7 }, "issues": [ "Taper arithmetic confirmed: r tan(alpha+phi) = 4.86 mm (mu 0.25) and 3.56 mm (mu 0.15), so 0.8 Nm gives 165-225 N. A thumb knob can therefore overload the tongue, as the analyst said.", "Tongue cantilever confirmed: sigma = 0.0536 MPa per N for 14 x 8 mm at 8 mm reach. With 3 / 4 / 6 MPa x 0.85 that is 48 / 63 / 95 N, which supports 25 / 60 / 100 N. The typical 60 N assumes an 8 mm thick tongue; thin 4-6 mm cams (the common printed design) give only 15-40 N.", "Peak is understated. The analyst's 250 N is a 'margin-adjusted' figure, but peak was meant to be the breaking load. 20-27 MPa in-plane (datasheet XY flexural strength is 73 MPa) divided by the sigma-per-N coefficient gives 370-500 N, and the hub, fillet and shaft bearing reduce that. I use 350 N. Peak is separate from sustained and does not change the ranking.", "Even 100 N serves only 25-50 mm of gasket at 2-4 N/mm, so a 700 mm path would need 15-35 cams. Seal suitability 2 stands. The taper over 90 deg (about 2.65 mm of draw-down) does give fine stroke control, but no hard stop is defined by the cam itself.", "The shaft hole bears on a printed hub: an M5 washer bears on about 55 mm2, so at 100 N the bearing is about 2 MPa, which is fine. Creep of the printed hole around the steel shaft is a real long-term loss but is not quantified.", "Zinc-plated shafts rust within months; specify A4. The Southco E5 cam latch figures (up to 2 mm compression, Flush Cup NEMA 4 / IP65, no holding force) confirmed from the cited page." ], "confidence": "medium", "reviewer_notes": "Independent recalculation: cam T/F 3.56-4.86 mm; tongue stress 0.0536 MPa per N; sustained allowables 3 / 4 / 6 MPa x 0.85 give 48 / 63 / 95 N. The analyst's typical of 60 N is reproduced within 5 percent. Source checks: the Elesa GN 927.2 page is live and states mu 0.25 plastic/plastic and 0.15 plastic/steel. For size 44 it lists 75 N manual force and 1450 N clamping force, as claimed (the page's extracted table has an unlabeled column with 33, which I ignored). The Southco/brandspurng page is live: roller cam gives up to 2 mm light-duty compression, Flush Cup meets NEMA 4 and IP65 with E5 or E3 latches, and no holding force is stated. The Polymaker TDS was read locally: XY tensile is 43.8 MPa, bending strength XY 73.4 MPa. The analyst's '37-44 MPa for Polymaker' is a misattribution, since 37 MPa is the Bambu figure from the brief. Specimens were 70 C chamber, 100 percent infill, and the sheet says not for design. The MakerWorld quarter-turn latch page is HTTP 403 and unverifiable; no printed-cam force data exists in the sources I could read. My search budget was exhausted, so I could not search for more. A cam latch is the weakest sealing mechanism here, and the force is limited by the tongue, not the hand. Confirmed, with peak raised.", "dead_or_misquoted_sources": [ "https://makerworld.com/models/3070853 - HTTP 403, unverifiable (compression-capable 90 deg latch, no force data).", "https://cdn.shopify.com/s/files/1/0603/6609/files/PolyLite_ASA_TDS_V5.1.pdf - cited for 'XY tensile about 37-44 MPa'; Polymaker's own XY value is 43.8 MPa (Z 32 MPa); 37 MPa is Bambu's figure. Specimen conditions (70 C chamber, 100 percent infill) flatter real parts." ] } }, { "id": "wedge-slide-bolt", "name": "Wedge / slide-bolt latch (tapered wedge into tapered catch)", "working_principle": "A flat tapered key (slope about 1:10) is pushed through a window in a tab that hangs through a catch block; the key wedges between the window edge and the catch face and pulls the lid down. At 1:10 the wedge self-locks against dry plastic friction (tan 5.7 deg = 0.10 < mu 0.15-0.25) and the 10:1 travel ratio gives very fine control of gasket squeeze. Printed flat with the pull load in-plane it needs no hardware. The ideal 10:1 force ratio is mostly lost to friction on the two faces, so hand push, not taper, sets the force.", "mechanical_advantage": "Ideal 1/tan(alpha) = 10:1 for a 1:10 taper (alpha = 5.71 deg). With friction on both faces the real force ratio F/P = 1 / (tan(phi2) + tan(alpha + phi1)) is about 1.6:1 at mu 0.25, 2.5:1 at mu 0.15 and 3.3:1 at mu 0.10 (own calc); a shallower taper barely helps because friction dominates. Release force is about 0.40 F (mu 0.25) or 0.20 F (mu 0.15). A captive M4 jack screw (nut factor 0.2) would add a further leverage of about 1250 N per Nm of screw torque.", "peak_clamp_force_N": 1400, "sustained_clamp_force_N": { "low": 250, "typical": 340, "high": 500 }, "limiting_factor": "Printed tab geometry: the end-cap beam below the window (bending in-plane) sets the sustained force, the net section of the tab legs at the window corners sets the break load; the practical ceiling is also the hand push (about 140-210 N needed for 340 N of clamp).", "force_basis": "calculated", "calculation": "ASSUMED PART (own): wedge key 10 mm wide x 40 mm long, 6 mm thick tapering to 2 mm (1:10, alpha 5.71 deg), sliding through a 10 mm wide window in a tab 26 mm wide x 8 mm thick; the key bears on the catch block's face above and on the 10 mm tall end cap of the window below. ASA, tab printed flat so the pull load is in the layer plane, 5-6 perimeters, 0.2 mm layers, key printed on its side with the taper profile in the XY plane so bearing loads are in-plane.\n1) Mechanical advantage with friction (own calc using P = F [tan(phi2) + tan(alpha + phi1)], friction 0.25 / 0.15 from https://elesa.com/en/elesab2bstoreca/Clamping-handles--Cam-levers--GN9272-A--d1): ideal 10; mu 0.25 both faces: P/F = 0.61, ratio 1.6; mu 0.15: 0.40, ratio 2.5; mu 0.10: 0.30, ratio 3.3. Pull-out force F [tan(phi2) + tan(phi1 - alpha)] = 0.40 F at mu 0.25 and 0.20 F at mu 0.15. Self-locking criterion tan(alpha) < mu (https://en.wikipedia.org/wiki/Wedge) holds for dry plastic but fails for wet, waxed or PTFE faces (mu under 0.1), and self-holding tapers in machining use only about 1.5 deg per side while steep 7:24 tapers self-release (https://en.wikipedia.org/wiki/Machine_taper); a 1:10 plastic wedge is in between, so add a detent.\n2) Structure (sustained, in-plane allowable 3 / 4 / 6 MPa for ASA at 60-70 C per the project brief, x 0.8 notch factor): (a) end-cap beam, span 10 mm, section 10 x 8 mm: Z = 133 mm3, M = F L / 8 = 1.25 F, sigma = 0.0094 MPa per N, giving 255 / 340 / 510 N (weakest, sets the result); (b) tab legs 2 x 8 x 8 = 128 mm2 net: 307 / 410 / 614 N; (c) window-edge bearing 10 x 8 = 80 mm2 at 8-10 MPa: 640-800 N. Peak at room temperature: legs 128 mm2 x about 37-44 MPa XY tensile (ASA datasheets, https://cdn.shopify.com/s/files/1/0603/6609/files/PolyLite_ASA_TDS_V5.1.pdf) / Kt 2.5 = about 1.4-1.6 kN; I report 1400 N.\n3) Hand drive (assumption, own): a thumb pushes about 50-100 N, giving 80-250 N of clamp at the real ratios 1.6-2.5; reaching 340 N needs about 140-210 N push (palm heel or a tap). An M4 jack screw pushing the wedge makes P = T / (0.2 x 4 mm); only about 0.15 Nm is needed for 340 N of clamp, whereas 1 Nm would give 2-3 kN and break the tab, so torque-limit it.\n4) Gasket stroke: at 1:10 each 1 mm of squeeze needs 10 mm of wedge travel, so +/-0.5 mm of wedge position is only +/-0.05 mm of squeeze, which handles the 0.2-0.75 mm stroke of a 3 mm bead far better than a fixed-travel latch. Stepped notches or a screw give an adjustable preload and a bottoming stop gives a defined squeeze.\n5) Result: sustained 250 / 340 / 500 N; peak 1400 N. At 100 mm latch pitch this is 2.5 / 3.4 / 5.0 N/mm, covering the 2-4 N/mm design window. No test data for a printed wedge latch exists; this is reasoning only. Further web searches were blocked (search budget exhausted).", "operating_force_N": 170, "preload_retention": "Fair. The wedge itself holds without back-off if the faces stay dry (self-locking), and its 10:1 travel means a loss of preload from TPU set (30-58 percent at 70 C, https://www.dream3d.co.uk/wp-content/uploads/2022/12/Ultrafuse_TPU_85A_TDS_EN_v2.5.pdf) can be recovered by driving the wedge a few mm further (stepped teeth or a screw). The ASA wedge faces and tab end cap also creep and relax under sustained hot load, and fretting wears the faces. A series spring (steel wave washer or flexible tab) would cut the TPU loss to about 10 percent (own calc, method from the brief).", "adjustable_preload": true, "positive_compression_stop": true, "scores": { "seal_suitability": 6, "outdoor_durability": 6, "printability": 8, "usability": 5 }, "best_materials": "ASA (default). UV-stabilised PC would raise the in-plane sustained limit about 1.3-1.5x (own judgement, unmeasured). PETG is marginal at 60-70 C; PETG-CF does not fix that. A stainless wear plate or PTFE tape on the wedge faces stabilises friction; avoid PA6-CF outdoors.", "hardware": "None required (fully printed). Optional: M4 A4 jack screw with captive nut to drive and lock the wedge, stainless or PTFE wear liner on the wedge faces, A4 spring plunger as a detent, wave washer as a series spring.", "design_guidelines": [ "Taper 1:10 to 1:15 (alpha 3.8-5.7 deg); do not go steeper than 1:8 or friction no longer holds. Smooth, ironed wedge faces with a dwell step or a detent notch every 1 mm of squeeze.", "Tab at least 8 mm thick, 26 mm wide, window 10 mm wide with end cap at least 10 mm tall and all window corners R at least 3 mm; legs at least 8 mm each. Print the tab flat so the pull load is in the layer plane.", "Print the wedge on its side with the taper profile in the XY plane; 5-6 perimeters, 0.16-0.2 mm layers.", "Set the wedge end-stop so full insertion gives 20-25 percent squeeze (about 0.75-0.8 x free bead height) and add a printed hard stop beside each latch.", "Add a detent or an M4 A4 jack screw to hold the wedge when wet, waxy or vibrated (mu under 0.1); torque-limit a jack screw to about 0.15 Nm.", "Use a pull tab or hole of at least 8 mm on the wedge for removal, since release takes 0.2-0.4 x clamp force (about 70-135 N).", "Keep the load line through the centre of the tab to limit the couple on the wedge; one wedge per tab, with latch pitch up to about 100 mm for a 2-4 N/mm gasket.", "Tether the wedge so it cannot be lost." ], "failure_modes": [ "End-cap beam cracks or legs tear at window corners (peel and brittle cracking in the cold).", "Wedge backs out in vibration or on wet or waxed faces (mu under 0.1), or when the TPU springs back.", "Face creep, fretting and wear lose preload; dirt, sand or ice jams the wedge.", "Over-driving with a hammer or jack screw cracks the tab.", "Cocking from the offset couple gives uneven squeeze at one end of the wedge.", "Wedge is lost if it is not tethered." ], "existing_designs": [], "sources": [ { "title": "Wikipedia: Wedge", "url": "https://en.wikipedia.org/wiki/Wedge", "note": "Fetched: ideal MA = 1/tan(alpha); binding (self-locking) when tan(alpha) < mu" }, { "title": "Wikipedia: Machine taper", "url": "https://en.wikipedia.org/wiki/Machine_taper", "note": "Fetched: self-holding Morse and Jacobs tapers about 1.4-2.3 deg per side versus self-releasing steep tapers (7:24)" }, { "title": "Elesa GN 927.2 page (friction coefficients)", "url": "https://elesa.com/en/elesab2bstoreca/Clamping-handles--Cam-levers--GN9272-A--d1", "note": "Fetched: plastic/plastic 0.25, plastic/steel 0.15" }, { "title": "Polymaker PolyLite ASA datasheet", "url": "https://cdn.shopify.com/s/files/1/0603/6609/files/PolyLite_ASA_TDS_V5.1.pdf", "note": "ASA XY tensile figures as given in the project brief, not re-fetched" }, { "title": "Ultrafuse TPU 85A datasheet", "url": "https://www.dream3d.co.uk/wp-content/uploads/2022/12/Ultrafuse_TPU_85A_TDS_EN_v2.5.pdf", "note": "Compression set 26 / 52 percent figures from the project brief, not re-checked" } ], "review": { "id": "wedge-slide-bolt", "verdict": "corrected", "peak_clamp_force_N": 1200, "sustained_clamp_force_N": { "low": 100, "typical": 200, "high": 400 }, "scores": { "seal_suitability": 6, "outdoor_durability": 5, "printability": 7, "usability": 4 }, "issues": [ "Wedge ratios confirmed: F/P = 1.64 (mu 0.25), 2.48 (mu 0.15), 3.31 (mu 0.10), with frictionless-guide formula P = F[tan phi + tan(alpha+phi)]. Release force is 0.40 F / 0.20 F, also confirmed.", "The 340 N typical is a structural number, not a deliverable one. It needs 207 N of push at mu 0.25 (136 N at mu 0.15). The analyst's own 'thumb 50-100 N' gives 80-250 N. The brief's comfortable range is 20-50 N, and release then needs 70-135 N pull. Applying the same hand-limited logic used for the cap and bayonet, typical is about 200 N, low about 100 N. Above about 250 N a tap, palm-heel or jack screw is needed (hardware, and torque-limit it).", "Structural check reproduced: end cap beam 0.0094 MPa per N (255 / 340 / 510 N at 3 / 4 / 6 MPa x 0.8) and tab legs 128 mm2 (307 / 410 / 614 N). These assume a uniform load across the 10 mm cap. If the wedge loads the cap centrally (M = F L/4) the cap numbers halve to 128 / 170 / 255 N. The peak arithmetic is also not reproducible: 128 mm2 x 37-44 MPa / Kt 2.5 = 1.9-2.25 kN, not 1.4-1.6 kN.", "The attachments are not analysed, and they are the likely limit. The tab cannot be printed flat if it is integral with a lid printed flat, so a flat tab means a separate part with a steel pivot pin or screw, which contradicts 'no hardware'. A pin M4 in an 8 mm printed tab at 8-10 MPa bearing allows only 256-320 N (M5: 320-400 N). The catch block is a cantilever shelf loaded across layers when the body is printed upright. These limit sustained to about 250-320 N and peak to about 1.2 kN, hence 220-300 N is the realistic ceiling.", "The self-locking statement is too pessimistic. For a wedge between two friction faces it holds when alpha < phi1 + phi2, not tan(alpha) < mu. At mu 0.10 the 5.7 deg wedge still holds (release force 0.1 F). The 7:24 machine taper (16.6 deg included) self-releases, consistent with 2 phi for steel. So wet or waxed faces are not the failure mode claimed. Real risks are fretting, dirt/ice jams and a lost wedge.", "Stroke control is the real advantage: 1 mm of squeeze needs 10 mm of travel, so +/-0.5 mm of position is +/-0.05 mm squeeze, and a recovered position fixes TPU set. At about 200 N and 100 mm pitch (2.0 N/mm) it just reaches the lower edge of the 2-4 N/mm window; 8 latches on a 700 mm path give about 2.3 N/mm. Seal suitability 6 is kept as the best of the four.", "Scores adjusted: durability 6 to 5 (unanalysed anchors, loose part, fretting under sustained hot load), printability 8 to 7 (a separate tab plus pivot or inserts), usability 5 to 4 (push and release forces well above 20-50 N, tethered loose wedge, no tests)." ], "confidence": "low", "reviewer_notes": "I reproduced the wedge ratios (1.64 / 2.48 / 3.31), the release forces, the end-cap beam (Z = 133 mm3, M = 1.25 F) and the leg net section (128 mm2). The analyst's structural arithmetic is internally consistent apart from the peak. The problem is what the 340 N represents. It is the beam limit for a 10 mm cap with a distributed load, not what a hand can push, and it ignores the pin/catch anchorage, which gives 256-400 N for an M4/M5 pin at the brief's 8-10 MPa bearing. Pushing 50-100 N at the real ratio gives 80-250 N, so I set typical 200 N (about 41 percent below the analyst), low 100 N, high 400 N, peak 1200 N. This is a calculation with no test data; the analyst found no existing printed wedge design, and my search budget was exhausted so I could not look for any. Source checks: Wikipedia Wedge fetched; it gives ideal MA = 1/tan(alpha) and a binding condition on the angle versus friction, which the analyst quoted correctly. Wikipedia Machine taper fetched; Morse about 1.49 deg per side, and 7:24 is steep and self-releasing; the analyst's '1.4-2.3 deg per side' is close. Elesa friction values confirmed. The Polymaker XY range is a misattribution (43.8 MPa is Polymaker's, 37 is Bambu's). Ultrafuse set 26/52 percent confirmed from the local PDF read. Wedge and cotter analysis is textbook (classical cotter joints: rod tension at the slot, end-cap bending and shear, bearing), but the printed-plastic allowables of 3 / 4 / 6 MPa are the brief's untested rule of thumb for ASA at 60-70 C.", "dead_or_misquoted_sources": [ "https://cdn.shopify.com/s/files/1/0603/6609/files/PolyLite_ASA_TDS_V5.1.pdf - cited for 'XY tensile about 37-44 MPa'; Polymaker's XY value is 43.8 MPa (Z 32 MPa), 37 MPa is Bambu's; specimen conditions (70 C chamber, 100 percent infill) flatter real parts.", "https://en.wikipedia.org/wiki/Wedge - live, but the cited tan(alpha) < mu self-locking criterion is for a single friction face; with friction on both faces it is alpha < phi1 + phi2, so the 'fails below mu 0.1' conclusion drawn from it is wrong.", "No existing printed wedge-latch design, force test or IP data was found or cited; the number is reasoning only." ] } }, { "id": "snap-fit-compliant", "name": "Snap-fit cantilever hook and compliant catches (incl. press-and-pull and TPU strap latches)", "working_principle": "A flexible arm (cantilever hook, annular snap, spring-loaded press-and-pull hook, bistable snap-through, or TPU/TPE strap) is deflected sideways while the lid closes. The hook slips past a ledge and the arm springs back so the hook sits behind the ledge. Holding is by geometric interference: the load goes through the arm as tension, and the arm relaxes to nearly zero strain once engaged. A rigid locking hook therefore adds no gasket preload. It only fixes the lid position, so the gasket force is whatever the tolerance stack gives. The one variant that stores preload is the stretched TPU/TPE strap or over-centre flexible draw latch, whose elastic stretch is the preload.", "mechanical_advantage": "About 1:1 for a locking hook, so the force at the lid equals the tension in the arm. Ramp geometry only governs insertion and removal: F_in = P(mu + tan a)/(1 - mu tan a). A pull-in wedge on the hook back face (10-20 deg) multiplies the arm's small spring force by only 1.1-1.6 at mu = 0.4. A TPU strap is also about 1:1 on strap tension, and an over-centre TPE latch such as the Gripwell C7 adds a small lever ratio.", "peak_clamp_force_N": 100, "sustained_clamp_force_N": { "low": 9, "typical": 20, "high": 45 }, "limiting_factor": "Two limits. (1) Strength: the thin arm and hook root carry tension plus eccentric bending at 60-70 C. Sustained nominal stress is only ~3-5 MPa, so one catch holds ~10-25 N for a rigid hook and ~20-45 N for a 12x3 mm TPU strap. (2) No usable preload: a stiff hook cannot store or maintain gasket squeeze, and the arm cannot be pre-stressed (creep-limited deflection gives ~2 N). Even at the 28 mm rim-bending pitch, 20 N is only ~0.7 N/mm of line load, about a third of the 2 N/mm floor of the design window.", "force_basis": "calculated", "calculation": "Rigid locking hook, ASA or PETG, arm printed flat. Assumed arm L = 25 mm, t = 2.5 mm, b = 10 mm, E = 1.8 GPa (the lead's assumed value), I = b t^3/12 = 13.0 mm^4. Snapping: root strain = 1.5 t y / L^2. At the 3 % flat-arm limit (buildcad.ai rule: 3 % flat, 1.5 % standing for PETG/ABS/ASA) y_max = 5.0 mm and tip force P = 3EIy/L^3 = 22.5 N. A typical 1.5 mm hook gives 0.9 % strain and P = 6.8 N. With a 30 deg lead-in and mu = 0.4 the insertion force is 8.6 N, inside the measured ABS insertion range of 3.2-32 N (IJAME). Retention: tension through the arm with the hook face offset e = t/2 + h_hook/2 = 2 mm. Stress is sigma = (F/A)(1 + 6e/t) = 5.8 F/A, with Kt ~ 1.5 at the root fillet. At sustained sigma = 3 / 4 MPa (cautious) on the 2.5x10 arm: F = 8.6 / 11.5 N. A stouter arm (3.5x12 mm) at 4 / 5 MPa gives 21 / 26 N. At short-term XY tensile strength ~35 MPa (Bambu/Polymaker ASA 37 / 43.8 MPa XY, from the lead) the same arms break at ~100 N (2.5x10) to ~185 N (3.5x12). That is above the measured 41 N peak of the ABS release-type hooks, because those hooks were ramped to release. Use ~100 N as the realistic peak. Preload from the arm's own spring: creep-limited deflection at 0.3 % strain is 0.5 mm, giving P = 2.3 N, so the arm cannot be the preload spring. TPU strap: 12x3 mm = 36 mm^2, E ~ 12 MPa (NinjaFlex 85A, lead's link), 10-20 % stretch gives 43-86 N initially. After 30-50 % relaxation at 60-70 C (Ultrafuse 85A set 26-52 % is a compression-set proxy) the sustained force is ~22-60 N. Hence low 9 / typical 20 / high 45 N. Line load at 28 mm pitch: 9 / 20 / 45 N is 0.3 / 0.7 / 1.6 N/mm versus the 2-4 N/mm window. Series stiffness (own calc): rigid arm EA/L = 1800 N/mm against ~175 N/mm gasket stiffness per catch (rib 1.2x2.4 mm, 3 N/mm at 0.48 mm, 28 mm pitch). Loss = set x ks/(kg+ks) = 0.91 x set, so a 30-58 % compression set removes 27-53 % of the force. A TPU strap (~11 N/mm) loses <1 % to gasket set but relaxes itself. Commercial anchors: Gripwell C7 over-centre flexible latch (TPE latch, glass-filled nylon link, stainless keeper) lists clamping force 49 N (small) and 176 N (large). Evidence note: the WebSearch budget was exhausted in this run. Only URLs supplied by the lead were re-fetched; MakerWorld, Printables and Pelican returned 403 and are marked unverified.", "operating_force_N": 10, "preload_retention": "Poor for rigid hooks. They are stiff (ks/(kg+ks) ~ 0.9), so 27-53 % of the force is lost to TPU compression set at 70 C. FDM hook-to-ledge slack of a few tenths of a mm is as large as the whole 0.2-0.75 mm gasket stroke, so the lid can lift and the force falls to ~0. Arm tension creep at 60 C adds loss. The TPU strap variant is much softer, so gasket set costs <1 %, but the strap relaxes 30-50 % itself and loses strength in UV (TPU 92A -15 % after 1000 h QUV, lead's Stratasys source).", "adjustable_preload": false, "positive_compression_stop": false, "scores": { "seal_suitability": 3, "outdoor_durability": 4, "printability": 9, "usability": 8 }, "best_materials": "ASA is the default (arm printed flat, 4+ perimeters, 0.2 mm or finer layers). UV-stabilised PC is tougher and creeps less, probably 1.3-1.5x higher limits (the lead's own judgement, unmeasured). PETG is marginal at 60-70 C (HDT 68 C). Avoid PLA and unstabilised PP. PA6-CF is out outdoors (3.3 % water uptake). For the strap variant use black UV-stabilised TPU or TPE/EPDM straps.", "hardware": "None for the printed hook. Optional A2/A4 stainless compression spring for press-and-pull variants. A stainless keeper with a radiused edge for TPU straps. A 3 mm stainless pin if the catch is hinged.", "design_guidelines": [ "Print arms lying flat so bending stress runs along the roads, and keep all hook and ledge loads in XY. A standing arm bears ~29 % (ASA, 17 vs 57 kg hook test) to 46 % (PETG) of the lying strength (CNC Kitchen).", "Snapping strain at the root <= 3 % flat or 1.5 % standing (strain = 1.5 t y / L^2). Lengthen the arm before thinning it. Typical arm L 25-30 mm, t 2.5-3.5 mm, b >= 10 mm (buildcad.ai says >= 5 mm).", "Root fillet >= 0.5 t and never under 0.4 mm. Aim for 1.5 mm in ASA, which has only ~3 kJ/m2 notched Charpy at -30 C.", "30 deg lead-in. Square or 3-5 deg undercut back face for a positive lock. Do not count on a pull-in wedge for preload (gain only 1.1-1.6).", "The engaged arm must be at ~0 strain, because sustained strain above ~0.3 % creeps at 60-70 C. Treat the snap as alignment and retention only.", "Space catches at or below the rim-bending pitch (~28 mm for a flat 3 mm lid edge, ~110 mm with a 20 mm skirt). Put a printed hard stop beside each catch at 0.75-0.8x the free bead height.", "Use snaps beside a screw, cam or band clamp that supplies the preload. If the gasket line load is above ~1 N/mm, a snap-only closure cannot hold it.", "TPU strap: 12-15 x 3 mm, 15-20 % stretch, 2-3 keeper positions for adjustment, UV-stabilised black, replaceable. Expect to retension it after the first hot summer." ], "failure_modes": [ "Root crack from cold or fatigue (sharp internal corners, standing arm)", "Hook lift-off from creep of the arm or ledge at 60-70 C, so the gasket force is lost", "Hook rotating out of the ledge under the eccentric closing load", "Gasket compression set shows up almost 1:1 as force loss (stiff hook)", "Rim bowing between catches leaves leak gaps", "TPU strap relaxation and UV embrittlement", "Vibration or thermal cycling unseating a bistable or press-and-pull catch", "Inconsistent squeeze from FDM tolerance, with no adjustment" ], "existing_designs": [ { "title": "MakerWorld Rugged Waterproof Tough Case 2385298 (PETG snap latches + TPU 85A gasket)", "url": "https://www.makerworld.com/en/models/2385298", "note": "Only printed-latch-plus-85A-TPU design known to the lead. No force or IP data. Re-fetch returned HTTP 403, so unverified." }, { "title": "zx82net ultimate parametric rugged box snap closure (Printables)", "url": "https://www.printables.com/model/59227-zx82net-ultimate-parametric-rugged-box-snap-closur", "note": "From the lead. Re-fetch returned HTTP 403, so unverified." }, { "title": "Thingiverse clip-latch rugged box with filament pins (harktech mirror)", "url": "https://harktech.co.uk/m/thingiverse/7208214", "note": "PLA+ 15 % infill, no test (from the lead; not re-fetched)." }, { "title": "Gripwell C7 flexible over-centre draw latch (commercial TPE reference, not printable)", "url": "https://www.gripwell.com.sg/image/catalog/Gripwell/Engineered Access Hardware/Latches/Draw Latches/C7 Flexible Draw Latch/Gripwell - C7 Flexible Draw Latch.pdf", "note": "Verified: clamping force 49 N small / 176 N large; TPE latch, glass-filled nylon link, stainless keeper. The lead's 'Southco EPDM' and -20 to 95 C figures were not found in this PDF." }, { "title": "Pelican Storm iM2435 spec sheet (PBT latch + EPDM O-ring)", "url": "https://www.pelican.com/us/en/product/cases/iM2435/pdf", "note": "Press-and-pull reference, no force published. Re-fetch returned 403." } ], "sources": [ { "title": "Analyzing insertion and retention forces in cantilever snap-fits (IJAME)", "url": "https://journal.ump.edu.my/ijame/article/view/11091", "note": "Verified: 16 printed ABS geometries, experimental insertion 3.2-32.2 N, retention 1.66-41.1 N; Model 5 highest retention, Model 2 lowest." }, { "title": "buildcad.ai snap-fit 3D printing rules", "url": "https://buildcad.ai/snap-fit-3d-printing", "note": "Verified: allowable strain PETG/ABS/ASA 3 % flat and 1.5 % standing, PLA 2 %/1 %; strain = 1.5 t y/L^2; fillet >= 0.5 t; arm width >= 5 mm; 30 deg lead-in. No retention formula or creep data." }, { "title": "CNC Kitchen: Comparing PLA, PETG and ASA (Prusament)", "url": "https://www.cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament", "note": "Verified: hook failure lying vs standing ASA 57 vs 17 kg, PETG 55 vs 25, PLA 73 vs 40; ASA softens 110 C, fails 120 C; PETG fails ~85 C." }, { "title": "Gripwell C7 flexible draw latch datasheet", "url": "https://www.gripwell.com.sg/image/catalog/Gripwell/Engineered Access Hardware/Latches/Draw Latches/C7 Flexible Draw Latch/Gripwell - C7 Flexible Draw Latch.pdf", "note": "Verified by decoding the PDF: clamping force 49/176 N, over-centre, TPE." }, { "title": "filamentspecs: creep resistance of 3D printed parts", "url": "https://filamentspecs.com/creep-resistance-3d-printed-parts/", "note": "Verified: bolted PETG joints lost ~11.5 % preload in 7 days vs ~3 % PLA. The page gives no numeric stress or temperature limits for ASA, PETG, nylon or PC." }, { "title": "Texin 985 datasheet (gasket stress and compression set)", "url": "https://sushengpolymer.com/media/pdf/phFiH7_Texin-985.pdf", "note": "From the lead's brief; not re-fetched. Gasket stiffness figures here are own calc from it." }, { "title": "Stratasys FDM UV ageing white paper", "url": "https://stratasys.com/siteassets/abm-pages/aerospace/wp_fdm_uv-aging_a4_0123a.pdf", "note": "From the lead (TPU 92A -15 % after 1000 h QUV, ASA -3 % break stress); not re-fetched." } ], "review": { "id": "snap-fit-compliant", "verdict": "confirmed", "peak_clamp_force_N": 90, "sustained_clamp_force_N": { "low": 8, "typical": 18, "high": 40 }, "scores": { "seal_suitability": 2, "outdoor_durability": 4, "printability": 9, "usability": 6 }, "issues": [ "Arithmetic reproduces: I = 13.0 mm^4, tip force 22.5 N at 3 % strain (y = 5 mm), 6.75 N at 0.9 % strain. Retention at the hook root is 8.6 / 11.5 N (3 / 4 MPa) for 2.5x10 mm and about 21 / 26 N for 3.5x12 mm. The analyst applies the 3-5 MPa allowable to the peak local stress (eccentric bending x Kt 1.5). That is conservative, because creep relieves Kt under static load. Without Kt the same arms hold 13-22 N and 21-40 N. The spread 9-45 N is therefore defensible, with the typical value slightly under 20 N.", "A rigid hook is not a clamp. At the design rib (3 N/mm at 0.48 mm, 28 mm pitch) the gasket pushes back about 84 N per hook, 4-8x what the hook can hold sustained. Holding 11-25 N means a squeeze of only 0.06-0.14 mm, below FDM warp and below the 0.2 mm minimum squeeze in the brief. A snap-fit cannot seal the design gasket, so seal_suitability 3 is pulled to 2.", "Usability 8 only holds for a very soft or sparse gasket. The user must compress the gasket by hand while the hook engages, and the design-window reaction is 1.4-2.8 kN on a 200x150 lid. Scored 6.", "The TPU strap loss to gasket set is stated as under 1 %. Recomputed: strap 36 mm^2 x 12 MPa / 40 mm = 10.8 N/mm against 175 N/mm of gasket, so ks/(kg+ks) = 0.058 and the set loss is 1.8-3.4 %. The strap's own stress relaxation at 60-70 C (30-50 %) still dominates.", "Peak of 100 N is an upper estimate. It comes from the in-plane XY strength (about 35 MPa) divided by eccentricity and Kt, which gives 86-115 N. The only measured retention data (IJAME, release-type ABS hooks) top out at 41 N, and the larger CNC Kitchen hook (57 kg lying) is a much stouter geometry. Used 90 N. This is a room-temperature break load, not a hot value.", "Evidence is thin. There is no sustained-load creep data for ASA or PETG at 60-70 C anywhere in the cited set. Dogan 2022 only shows ABS rupturing in about 3 min at 60 C and 20 MPa (milled specimens, 3 h tests). The 3-5 MPa rule is untested judgement.", "The Gripwell 49 / 176 N figures are catalogue 'clamping force' ratings. The PDF does not say whether they are working, sustained or break loads. The Southco and temperature claims are not in the PDF, as the analyst already noted. Treat the PDF as an order-of-magnitude anchor for a TPE draw latch only." ], "confidence": "medium", "reviewer_notes": "Independent recalculation (Python, same inputs): cantilever P = 3EIy/L^3 = 22.5 N, strain = 1.5 t y/L^2 = 3.0 % at y = 5 mm. Eccentric hook factor 1 + 6e/t = 5.8 (e = 2 mm, t = 2.5 mm). Sustained F = sigma A / (5.8 x 1.5) = 8.6 / 11.5 / 14.4 N at 3 / 4 / 5 MPa. Without Kt: 12.9 / 17.2 / 21.6 N. Stouter 3.5x12 arm, e = 2.5 mm: 21 N (Kt) to 32 N (no Kt) at 4 MPa. TPU strap 12x3 mm at 10-20 % stretch gives 43-86 N, then 30-50 % relaxation gives 22-60 N. Gasket stiffness per catch is 175 N/mm, arm stiffness is 1800 N/mm, so ks/(kg+ks) = 0.91. This matches the analyst (27-53 % loss). My typical of 18 N lies within about 10 % of the analyst's 20 N, and the key sources check out, so the verdict is confirmed. Scores are pulled back for seal and usability. A hook adds essentially no preload, so it is only a position-keeper beside a real clamp. Verified by fetch: buildcad.ai strain limits (PETG/ABS/ASA 3 % flat, 1.5 % standing, strain = 1.5 t y/L^2, fillet >= 0.5 t, arm >= 5 mm wide); IJAME (16 printed ABS models, insertion 3.23-32.18 N, retention 1.66-41.14 N, arm dimensions not on the page); CNC Kitchen hook test (ASA 57 vs 17 kg, PETG 55 vs 25, PLA 73 vs 40; ASA softens 110 C and fails 120 C; PETG fails about 85 C); filamentspecs (PETG joint lost about 11.5 % preload vs about 3 % PLA over 7 days, no conditions given); Gripwell C7 (49 N small, 176 N large, TPE latch, glass-filled nylon link, stainless keeper). MakerWorld 2385298 returns HTTP 403 for me too, so it stays unverified.", "dead_or_misquoted_sources": [ "https://www.makerworld.com/en/models/2385298 returned HTTP 403 on re-fetch, so the 'only printed latch plus TPU 85A gasket design' claim cannot be checked", "https://www.printables.com/model/59227-zx82net-ultimate-parametric-rugged-box-snap-closur and https://www.pelican.com/us/en/product/cases/iM2435/pdf were reported 403 by the analyst; I did not re-check them", "https://journal.ump.edu.my/ijame/article/view/11091 is quoted correctly but gives no arm dimensions and does not define 'retention force'. It cannot support a locking-hook sustained load", "https://filamentspecs.com/creep-resistance-3d-printed-parts/ is quoted correctly (11.5 % vs 3 %) but the page gives no bolt, preload, stress or temperature, and itself warns against transferring the percentages", "https://sushengpolymer.com/media/pdf/phFiH7_Texin-985.pdf: the compression table is an embedded raster image, so my fetch could not read it. The gasket stiffness inputs are not independently verified by me" ] } }, { "id": "perimeter-band-clamp", "name": "Perimeter band clamp (V-band / Marman / flange clip clamp / strap buckle band)", "working_principle": "A band or hinged ring halves with V-shaped (about 20 deg) shoes is tensioned around matching conical or chamfered flanges on lid and body. The tension gives a radial line load T/r. The wedge faces turn that radial load into an axial force pushing the two flanges together, around the whole perimeter, so the gasket is loaded uniformly instead of at points. The tension comes from a T-bolt, thumbscrew or over-centre buckle. Only round or oval flanges work. Straight spans of a rectangular lid do not take hoop-wedge loading.", "mechanical_advantage": "Wedge: F_ax,total = pi T (1 - mu tan th)/(tan th + mu) with th = 20 deg (face angle to the flange plane) and mu = 0.3. That is 4.2 T ideal, and I use ~3 T after a 0.7 derate for circumferential friction and uneven tension. This is independent of band diameter (confirmed by Barrans et al. FEA for 20 deg half-section and T-bolt loads < 7 kN). The closure adds more: M5 T-bolt at K = 0.2 turns 0.3 N.m into T = 300 N, or an over-centre buckle at about 8:1. The axial stroke is only tan 20 = 0.36x the radial movement per face, which damps creep sensitivity.", "peak_clamp_force_N": 3600, "sustained_clamp_force_N": { "low": 450, "typical": 900, "high": 1800 }, "limiting_factor": "The printed ring and flange, not the steel band. Hoop compression in the flange ring equals T (6 MPa at T = 300 N on an 8x6 mm section), and the radial line load T/r (5 N/mm at T = 300, r = 60) loads a thin printed shell near its buckling limit. A long 3 mm shell at R = 60 buckles at ~0.06 MPa (own calc). Printed clamp halves in tension carry only ~100-160 N (4x8 mm, 3-5 MPa), so a steel band plus thick or insert-reinforced rings is needed. Needs round or oval flanges, so per-latch comparison with other mechanisms is not meaningful. Numbers are the total axial force of the whole closure.", "force_basis": "calculated", "calculation": "Own derivation. Per wedge face the normal force is N, with axial component N(cos th - mu sin th) and radial component N(sin th + mu cos th), two faces per segment. Hence F_ax,total = pi T (1 - mu tan th)/(tan th + mu). For th = 20 deg: mu = 0.15 gives 5.8 T, mu = 0.30 gives 4.2 T, mu = 0.45 gives 3.2 T (rough printed cone faces fall at the low end). The radial load is 1.49x the axial line load at mu = 0.3. A linear axial-vs-T-bolt relation, independent of band diameter for T-bolt loads under 7 kN, is confirmed by Barrans et al. (Open Eng. 2015) with 20 deg half-section. They also report that wedge angle and friction strongly affect stiffness. The lead's 'over-predicts' remark was not found in that paper. With a 0.7 derate F_ax = 3 T. Example round lid D = 120 mm (circumference 377 mm). T = 150 / 300 / 600 N gives F = 450 / 900 / 1800 N, i.e. 1.2 / 2.4 / 4.8 N/mm line load. The 2-4 N/mm window needs T = 250-500 N, so the typical case sits inside it. Stainless 316 band 12x0.6 = 7.2 mm^2: T_allow at 250 MPa (SF ~2) = 1.8 kN, so the band is never the limit. Flange ring compression is T over section: 3.1 / 6.3 / 12.5 MPa for 8x6 mm. The high case needs a 12x8 mm or metal ring (6.3 MPa). Printed halves in hoop tension (4x8 / 6x10 mm, 3-5 MPa) carry 96-160 N / 180-300 N, hence the steel band. Peak: T_peak ~ 1.2 kN (ring compression ~25 MPa), so F_peak ~ 3.6 kN. Hand effort: M5 T-bolt torque 0.2 T d = 0.3 N.m at T = 300, about 25 N finger force on a 12 mm wing-nut arm. Series stiffness: steel band dT/dr = EA/r = 193000x7.2/60 = 23.2 kN/mm. Axial stiffness = 3 x 23.2 / (2 tan 20) = 95 kN/mm, against gasket ~2.4 kN/mm around D = 120 (rib 3 N/mm at 0.48 mm). A rigid band therefore loses ~29-51 % force to a 30-52 % set. A T-bolt spring of 23 N/mm (13 mm travel at 300 N) gives ks = 0.25 kg and cuts the loss to 6-10 %. A 50 N/mm spring (6 mm travel) gives 11-18 %. For a 200x150 lid (700 mm path) only an oval or rounded band is plausible, and its straight spans bow, so use round Ds of 100-200 mm (D = 200 needs T ~ 630 N for 3 N/mm). Evidence note: the WebSearch budget was exhausted in this run. Sources are the lead's URLs, re-fetched where possible, plus own derivation.", "operating_force_N": 25, "preload_retention": "Moderate if fixed, good with a series spring. A rigid steel band on rigid V-flanges has ~95 kN/mm axial stiffness against ~2.4 kN/mm for the gasket, so it carries 29-51 % loss from TPU compression set. A stainless compression spring in the T-bolt (20-50 N/mm, 6-13 mm travel at T = 300 N) cuts that to 6-18 %. The wedge helps because 0.1 mm of radial creep in the printed V faces costs only ~0.073 mm axial. Printed shoes and rings under 6 MPa compression at 60 C will still creep, so retension after the first hot spell.", "adjustable_preload": true, "positive_compression_stop": true, "scores": { "seal_suitability": 7, "outdoor_durability": 6, "printability": 6, "usability": 6 }, "best_materials": "Band: A4/316 stainless 12x0.6 mm. Printed V-shoes and flange rings: ASA, 100 % infill, 4+ perimeters. UV-stabilised PC for more creep margin (probably 1.3-1.5x, the lead's judgement). PETG is only acceptable if kept below ~60 C. Avoid PA6-CF outdoors. Use an aluminium or steel insert ring if T > 300 N.", "hardware": "A2/A4 stainless band 12x0.6 mm (strap or hose-clamp style), M5 stainless T-bolt with trunnion or an over-centre buckle, stainless compression spring (20-50 N/mm), all-metal lock nut or thread-locker, optional steel or aluminium ring insert.", "design_guidelines": [ "Wedge half-angle ~20 deg (as in the Barrans V-band model). Keep cone faces smooth: print the ring axis-vertical with the cone face on top, 0.12-0.16 mm layers, light sanding and a dry lube, so mu stays 0.15-0.3. At mu = 0.45 the axial gain falls from 4.2 T to 3.2 T.", "Orient the ring axis vertical so the hoop load runs along the roads. Use 100 % infill and 4+ perimeters, with ring section >= 8x6 mm radial x axial for T <= 300 N (12x8 mm for 600 N).", "Support the flange ring on a spigot or step. Do not clamp a free 3 mm shell, because the radial line load is 1.5x the axial line load.", "Put a flange land (1.5-2 mm) as the hard stop, so the V faces bottom at 20-25 % gasket squeeze. Keep gasket groove depth and rib height matched to that.", "Use 6-10 printed shoe segments (each <= 45 deg arc) under a continuous 12 mm steel band, or two printed half-rings with a hinge and one T-bolt only at modest T.", "Use a series spring in the T-bolt: ~20-25 N/mm with 13 mm travel, or 50 N/mm with 6 mm travel, set to the target T at mid-travel. Mark torque (0.3 N.m for T = 300 N with M5).", "Minimum practical diameter ~100-110 mm (Barrans' classical model validated for D > 110 mm, and small bands go non-linear at lower T-bolt load). For smaller Ds use individual flange clips or lugs (Blue Robotics style).", "Orient the T-bolt low or at the side, and use stainless against stainless, with A2/A4 fasteners. Retension after the first hot day." ], "failure_modes": [ "Ring buckling or ovalising of a thin printed shell under the radial line load", "V-shoe or flange creep at 60-70 C loosening the band", "T-bolt self-loosening in vibration", "Band tension uneven near the T-bolt, giving uneven squeeze", "Shoe riding over the flange (irrecoverable separation) if the angle is too steep or the stroke too large", "Out-of-round or warped flanges (FDM warp 0.3-1 mm) opening a leak gap", "Rough cone faces (mu 0.45+) cutting axial gain by a quarter", "Cracked printed trunnion or clevis under T-bolt pull-out" ], "existing_designs": [ { "title": "Blue Robotics forum: printed enclosure end-cap clips (BlueROV2)", "url": "https://discuss.bluerobotics.com/t/enclosure-clips/2854", "note": "Verified: printed clips made about 2x the size of the aluminium ones 'worked fine'. No material, load or force given. These are discrete flange clips, not a V-band." }, { "title": "MakerWorld quick-release strap locks with loop retention (bistable cam strap lock)", "url": "https://makerworld.com/ja/models/463867-quick-release-strap-locks-with-loop-retention", "note": "From the lead. Re-fetch returned 403, so unverified. No force data known." }, { "title": "MakerWorld ASA double D-ring buckle strap", "url": "https://makerworld.com/en/models/674852-double-d-ring-buckle-strap", "note": "From the lead; not re-fetched." }, { "title": "Printables Field Repair Buckle", "url": "https://www.printables.com/model/1247230-field-repair-buckle", "note": "From the lead. Re-fetch returned 403, so unverified." } ], "sources": [ { "title": "Barrans, Khodabakhshi, Muller: Classical and numerical approaches to determining V-section band clamp axial stiffness (Open Eng. 2015)", "url": "https://eprints.hud.ac.uk/id/eprint/22987/1/eng-2015-0010.pdf", "note": "Read by decoding the PDF. 20 deg half-section angle (Table 1), 193-227 GPa steel band, axial clamping load linear in T-bolt load below ~7 kN and independent of band size, pretension and friction increase axial load, classical model agrees with FEA for D > 110 mm. This is a stiffness paper; no ultimate-capacity over-prediction claim found." }, { "title": "Axial load capacity of V-section band clamp joints (Huddersfield, turbocharger conference 2006)", "url": "https://pure.hud.ac.uk/en/publications/axial-load-capacity-of-v-section-band-clamp-joints/", "note": "Verified abstract only: prediction method including circumferential and transverse friction, theory shown accurate in experiment. No numbers." }, { "title": "Wikipedia: Marman clamp", "url": "https://en.wikipedia.org/wiki/Marman_clamp", "note": "Verified qualitative description only: circumferential tension wedges the V-groove over the flanges. No angle or load figures." }, { "title": "Blue Robotics forum: enclosure clips", "url": "https://discuss.bluerobotics.com/t/enclosure-clips/2854", "note": "Verified: printed clips about 2x aluminium size worked; no force numbers." }, { "title": "CNC Kitchen: comparing PLA, PETG and ASA", "url": "https://www.cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament", "note": "Verified: lying vs standing hook strength; ASA softens 110 C." }, { "title": "Lee Spring: music wire vs stainless steel", "url": "https://www.leespring.com/music-wire-versus-stainless-steel", "note": "Verified: music wire rusts and tops out ~121 C; 302/304 stainless to ~288-316 C and weaker. Use stainless springs outdoors." }, { "title": "CNC Kitchen: carbon fibre nylon PA6 vs PA12 tested (bolt preload)", "url": "https://www.cnckitchen.com/blog/carbon-fiber-nylon-in-3d-printing-pa6-vs-pa12-tested", "note": "Verified: M4 at 0.8 N.m, one week; PA6 needed re-tightening almost daily, PA12 once at a level similar to PLA and ASA. Supports using steel for the tension path." } ], "review": { "id": "perimeter-band-clamp", "verdict": "corrected", "peak_clamp_force_N": 2500, "sustained_clamp_force_N": { "low": 400, "typical": 800, "high": 1400 }, "scores": { "seal_suitability": 6, "outdoor_durability": 5, "printability": 6, "usability": 6 }, "issues": [ "Wedge formula reproduces: F/T = pi (1 - mu tan a)/(tan a + mu) with a = 20 deg gives 5.78 / 4.21 / 3.23 at mu = 0.15 / 0.30 / 0.45. The Barrans paper does use a 20 deg half-section angle, and its equations treat radial force as axial force x tan(alpha), so the angle is measured from the radial plane as assumed. The 0.7 derate gives 2.95 T. Series stiffness also reproduces: band 23.2 kN/mm radial, 95 kN/mm axial, gasket 2.36 kN/mm at D = 120, so ks/(kg+ks) = 0.976 and the loss is 29-51 %.", "The recommended printed ring section is too thin. 8x6 mm at T = 300 N gives 6.25 MPa hoop compression, above the 3-5 MPa cautious rule. A free ring buckles at w_cr = 3EI/R^3 = 6.4 N/mm (E = 1.8 GPa) or 4.3 N/mm at a hot modulus of about 1.2 GPa, against the 5 N/mm applied at T = 300, R = 60. It would ovalise. At 10x8 mm (80 mm^2) the stress is 3.75 MPa and w_cr is 16.7 / 11.1 N/mm. That is the minimum for T of about 300 N, or the ring needs a spigot or metal insert. The typical 900 N survives only with this change. Printed ASA-on-ASA cone faces are more likely mu 0.4 than 0.3, which gives F = 2.5 T after the derate.", "The peak of 3.6 kN is inconsistent with the stated ring sizes. A free 8x6 ring buckles at T of about 380 N (about 1 kN axial). A free 10x8 ring buckles at T of about 1000 N, which gives about 2.5 kN axial at 2.5 T. Peak reduced to 2.5 kN.", "The force is for the whole closure on a round or oval flange (D = 120 mm, 377 mm path), not per latch. It cannot be compared with the 700 mm rectangular reference lid. Straight spans do not take hoop-wedge loading. At D = 120 a typical 800 N is 2.1 N/mm, inside the 2-4 N/mm window only because the path is short.", "No source measures a printed V-band. Barrans et al. model a steel band (13 mm^2, 227 GPa) on stiff steel flanges and report stiffness, not capacity. The 20 deg angle, linearity below 7 kN T-bolt load, independence from band size and the D > 110 mm validity are all confirmed. Huddersfield 2006 is an abstract only. Wikipedia is qualitative. Blue Robotics shows only that discrete printed clips about 2x the aluminium size 'worked fine', with no loads, material or pressure.", "The M5 T-bolt torque check (0.2 T d = 0.3 N.m, 25 N on a 12 mm arm) assumes K = 0.2. Stainless on stainless typically galls at K = 0.25-0.35, which gives 30-42 N finger force, the top of the comfortable 20-50 N range. The T-bolt should have a spring and lubricant.", "Durability and retension. Printed shoe faces and rings creep under 4-6 MPa at 60 C, so retensioning after the first hot spell is required. Seal 7 is reduced to 6 and durability 6 to 5 for that and for the round-only restriction." ], "confidence": "medium", "reviewer_notes": "Independent recalculation: F/T = 4.21 at mu 0.3, 3.51 at mu 0.4, 3.23 at mu 0.45. Taking the 0.7 derate gives 2.95 / 2.46 / 2.26 T. Hoop compression in the ring equals T, because line load T/r times r. Ring stress at T of 300 N is 6.25 MPa on 48 mm^2, 3.75 MPa on 80 mm^2, 6.25 MPa on the analyst's 600 N / 96 mm^2 case. Free-ring buckling load is w = 3EI/R^3 (R = 60 mm), which is 6.4 / 16.7 / 28.8 N/mm for 8x6 / 10x8 / 12x8 rings at E = 1.8 GPa. Long thin 3 mm cylinder buckling is 0.064 MPa, so the printed shell must be supported by the wall behind it. Sustained force with a 4 MPa allowable: 8x6 gives T = 192 N and about 480-576 N; 10x8 gives T = 320 N and about 800-960 N; 12x8 gives T = 384 N and about 960-1150 N. A metal insert or 5 MPa allowable gives about 1.4 kN. Torque and series-stiffness numbers reproduce. My typical of 800 N is 11 % below the analyst's 900 N and the sources check out. I used 'corrected' because the ring spec, the peak (-30 %) and two scores had to change. Verified by fetch: Barrans PDF (read by decoding the PDF: Table 1, 20 deg half-section, steel band 227 GPa, 13 mm^2, 1.3 mm thick; Fig. 10 text: axial load similar across band sizes for T-bolt loads below 7 kN; classical model agrees with FEA for D > 110 mm; the limit of linearity occurs at lower T-bolt load for smaller bands); Huddersfield abstract (accounts for circumferential and transverse friction, no numbers); Wikipedia Marman clamp (qualitative); Blue Robotics forum (printed clips about 2x aluminium size worked fine); Lee Spring (music wire above 121 C weakens, stainless is superior outdoors).", "dead_or_misquoted_sources": [ "https://eprints.hud.ac.uk/id/eprint/22987/1/eng-2015-0010.pdf is quoted correctly, but it is a stiffness paper. The analyst's note that it contains no over-prediction claim is right. It cannot support any capacity or printed-ring number", "https://pure.hud.ac.uk/en/publications/axial-load-capacity-of-v-section-band-clamp-joints/ is an abstract only, with no numbers", "https://makerworld.com/ja/models/463867-quick-release-strap-locks-with-loop-retention, https://www.printables.com/model/1247230-field-repair-buckle and https://makerworld.com/en/models/674852-double-d-ring-buckle-strap were not verifiable (403 per the analyst; I did not re-check). No force data is known for them", "https://www.leespring.com/music-wire-versus-stainless-steel: the page gives 550-600 F (288-316 C) for stainless in general, not specifically for 302/304. The 25-30 % weaker figure is a derived estimate, not stated on the page", "https://sushengpolymer.com/media/pdf/phFiH7_Texin-985.pdf: the compression table is a raster image and could not be read by my fetch. The gasket stiffness behind the series-stiffness numbers is unverified by me" ] } }, { "id": "multi-point-rod-latch", "name": "Multi-point rod latch (handle drives rods or bellcranks to top and bottom latch points)", "working_principle": "A handle turns a pinion, cam or crank. That drives two or more rods (or cables) in guides to latch points at the top, bottom and sometimes the sides of the door. Each point has a ramped hook or roller that pulls the door against a keeper, so one handle motion pulls the door at several places. The hand effort is shared between the rods. The closing force summed over all points is therefore set by the handle, not multiplied by the number of points. Printed parts would be housings, guides, bellcranks and keepers. The rods and pins should be steel.", "mechanical_advantage": "Handle 80 mm / pinion 8 mm = 10:1, efficiency 0.7, gives 7:1 to total rod force. A 15 deg rod ramp (mu 0.15-0.3) adds a wedge factor (1 - mu tan a)/(tan a + mu) = 1.6-2.3. Total handle-to-axial is ~11-16:1, shared by all points. A 4-point door gets half the per-point force of a 2-point door for the same handle effort.", "peak_clamp_force_N": 700, "sustained_clamp_force_N": { "low": 120, "typical": 250, "high": 450 }, "limiting_factor": "Hand effort shared across points (~0.6-0.8 kN total on the door for 50 N at an 80 mm handle, whatever the number of points), then bearing stress under the steel pins in the printed bellcranks and guides (a 4 mm pin in 8 mm thickness = 32 mm^2 gives 256 N at 8 MPa). Hinge-side compression comes only from lid stiffness and hinge position. Does not fit the 70x35x30 mm latch envelope, since the rods and handle run the whole door span.", "force_basis": "estimated", "calculation": "Own first-principles estimate. No published rating or test for printed multi-point latches was found; the cited article gives no numbers. Assumed hand force 50 N on an 80 mm handle, pinion radius 8 mm, efficiency 0.7. Total rod force F_t = 50 x 80/8 x 0.7 = 350 N, split over 2 rods = 175 N each. Ramp 15 deg: axial per point = 175 x 1.62 (mu 0.3, printed ramp) = 283 N, or 175 x 2.30 (mu 0.15, steel on steel) = 402 N. Total on the door = 570-800 N. With 4 points the per-point force halves to ~140-200 N. Bearing check: 4 mm pin x 8 mm bellcrank = 32 mm^2, which at 5 / 8 / 10 MPa (the lead's sustained bearing rule ~8-10 MPa) gives 160 / 256 / 320 N. 5 mm pin x 10 mm = 50 mm^2 gives 250 / 400 / 500 N. Short-term bearing ~22 MPa on 32 mm^2 gives ~700 N (peak). Keeper ramp 12x6 mm = 72 mm^2: 300 N is 4.2 MPa (fine). A 4 mm stainless rod 60 mm unsupported has Euler load 6.6 kN (not limiting). Summary: low 120 N (4-point door, hot, 5 MPa), typical 250 N, high 450 N (5 mm pin, thicker lever). Compared with the reference lid: 4 points x 250 N = 1.0 kN, which is 36-71 % of the required 1.4-2.8 kN total. To reach 2.8 kN by hand the handle torque would need to be about 14 N.m (about 3.5x a normal handle), so this suits a gasket at the 1-2 N/mm end or a stiffer, larger handle. Stiffness: 4 mm steel rod 400 mm long has EA/L = 6,000 N/mm. Stiffness is then set by printed pins and ramps, so most of the gasket compression set shows up as force loss unless the linkage has adjusters or a spring. Evidence note: the WebSearch budget was exhausted in this run, so no more sources were collected; confidence is low.", "operating_force_N": 50, "preload_retention": "Moderate with adjusters, weak without. Steel rods are very stiff (~6,000 N/mm), so the linkage cannot absorb gasket compression set. Printed bellcrank pin bores and ramps creep under 5-8 MPa bearing at 60 C. Expect roughly 25-55 % loss in the first hot season unless the keepers or rod-end clevises are adjustable and the handle cam over-centre includes a spring.", "adjustable_preload": true, "positive_compression_stop": false, "scores": { "seal_suitability": 5, "outdoor_durability": 6, "printability": 4, "usability": 7 }, "best_materials": "ASA for housings, guides and bellcranks, in thick solid sections. UV-stabilised PC if more creep margin is needed (probably 1.3-1.5x, the lead's judgement). Not PETG at 60-70 C. Steel parts: A2/A4 stainless rods, pins and keepers. PA6-CF is out outdoors.", "hardware": "A2/A4 stainless rods or flat bar (4-5 mm), M4/M5 stainless clevis rod ends, 4-5 mm stainless pins with e-clips, stainless keepers or rollers, a handle with cam or pinion, a spring or over-centre detent, and heat-set inserts for adjusters.", "design_guidelines": [ "Keep the handle lever long (>= 80-100 mm) and the pinion small (6-8 mm), but design all printed load paths for a 100 N worst-case hand force and the peak ~700 N per point.", "Use steel pins >= 4-5 mm through printed levers at least 8-10 mm thick (bearing <= 8 MPa sustained). Put pin axes along Z and print the lever flat, so bearing loads run in XY.", "Make ramp keepers 12x6 mm or larger, ramp angle 12-15 deg, lubricated stainless or PTFE contact. Add a printed hard stop beside each point at 0.75-0.8x the free bead height.", "Place latch points so the pull is near the gasket and not out at the corners. On a hinged lid the hinge side is compressed only by lid stiffness, so add a hinge-side lug or stiffen the rim.", "Rod-end clevises or keeper screws at every point for adjustment. Include a spring in the handle linkage (about 4x softer than the gasket per point) to cut the loss from compression set to < 10 %.", "Guide the rods every 60 mm or less. Stainless rod unsupported 60 mm is fine against buckling, but printed guide bores need 0.3-0.4 mm clearance and 4+ perimeters.", "Do not use this on small lids. Per-point force is about the same as a single compression latch, so the benefit is only load spreading on large lids with a stiff rim.", "Seal the rod entry points with small gaskets or boots, because rods passing through the box wall are a leak path." ], "failure_modes": [ "Printed bellcrank or guide bore elongation (bearing creep) giving backlash and loss of pull-in", "Hinge side under-compressed, causing a leak at the hinge side", "Rod binding from FDM warp or misaligned guides", "Seized or corroded linkage (mixed metals)", "Handle effort too low to hit the gasket force, so the door only closes partway", "Uneven squeeze between points from different rod lengths or keeper wear", "Ramp wear and slip under vibration" ], "existing_designs": [], "sources": [ { "title": "Magazine Industry USA: getting the latch and hinge specification right", "url": "https://www.magazine-industry-usa.com/news/1936-getting-the-latch-and-hinge-specification-right", "note": "Verified: only qualitative. Multi-point latching for large door spans, compression latches suit gasket sealing and vibration. No force, span or latch-count figures." }, { "title": "GlobalSpec: gasket latches", "url": "https://www.globalspec.com/ds/3851/areaspec/features_gasket", "note": "From the lead. Re-fetch returned HTTP 403, so unverified." }, { "title": "CNC Kitchen: helicoils, threaded inserts and embedded nuts strength", "url": "https://www.cnckitchen.com/blog/helicoils-threaded-insets-and-embedded-nuts-in-3d-prints-strength-amp-strength-assessment", "note": "Verified: M3 in PETG pull-out averages 119 kg heat-set insert, 118 kg direct screw, 86 kg side-pocket nut, 166 kg bottom-pocket nut (room temperature, flat 4-perimeter 100 % infill coupons). Bearing in the printed lever, not the thread, is the limit." }, { "title": "CNC Kitchen: comparing PLA, PETG and ASA", "url": "https://www.cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament", "note": "Verified: standing hooks only 29 % (ASA) of lying strength, so put lever and bearing loads in XY." }, { "title": "filamentspecs: creep resistance of 3D printed parts", "url": "https://filamentspecs.com/creep-resistance-3d-printed-parts/", "note": "Verified: PETG bolted joint lost ~11.5 % preload in 7 days vs ~3 % PLA." } ], "review": { "id": "multi-point-rod-latch", "verdict": "corrected", "peak_clamp_force_N": 600, "sustained_clamp_force_N": { "low": 60, "typical": 150, "high": 300 }, "scores": { "seal_suitability": 4, "outdoor_durability": 5, "printability": 4, "usability": 6 }, "issues": [ "Internal inconsistency. The analyst's own chain gives a hand-limited TOTAL of 350 N rod force x 1.62 = 567 N (mu 0.3) or x 2.30 = 804 N (mu 0.15) on the whole door. The summary then states 'typical 250 N per point' and '4 points x 250 N = 1.0 kN'. One handle cannot deliver 1.0 kN. For a 4-point door the closing force per point is 142 N (mu 0.3) or 201 N (mu 0.15). For a 2-point door it is 283 / 402 N.", "Sustained force must also allow for gasket set. With a stiff rod and pin chain, 25-55 % is lost, which leaves 64-106 N per point (4-point, mu 0.3) or 128-213 N (2-point). A series spring that holds the loss to 10 % gives 128-181 N (4-point) or 255-362 N (2-point). The typical value drops from 250 N to 150 N, with 60 N for a hot stiff 4-point door and 300 N for a spring-compensated 2-point door, which is bearing-limited anyway.", "The door total of 0.25-0.8 kN is 0.35-1.15 N/mm on a 700 mm path, below the 2 N/mm floor of the design window. The analyst's 'handle would need about 14 N.m' used mu 0.15. At mu 0.3 the handle torque for 2.8 kN is about 20 N.m, roughly 5x a 4 N.m hand effort. Seal 5 is reduced to 4.", "The handle is itself a load path. A 12x5 mm printed handle bending section at 50 N x 80 mm sees 80 MPa, double the strength of ASA. It needs about 20x10 mm (12 MPa) or a steel handle. The brief's comfortable finger force is 20-50 N, so 50 N is the upper end. Printed levers and bellcranks must be designed for the 100 N overload case, which is where the 600-700 N peak per point comes from.", "Peak. Bearing under a 4 mm pin x 8 mm is 32 mm^2 x 22 MPa = 700 N at the instantaneous (not sustained) level. A hand overload of 100 N at mu 0.3 gives about 570 N per point for a 2-point door. Peak set at 600 N per point.", "Sources give no force data. The Magazine Industry page is purely qualitative (multi-point latching for large spans, compression latches for gaskets, no numbers). GlobalSpec is not verifiable. The CNC Kitchen insert data are M3 axial pull-out values (PETG: insert 119 kg, direct screw 118, side-pocket nut 86, bottom-pocket nut 166) from flat 4-perimeter 100 % infill coupons. The page does not state test temperature or orientation, and none of it is a bearing or sustained value. Existing_designs is empty, so there is no printed example. The force_basis 'estimated' is honest.", "Does not fit the 70x35x30 latch envelope; rods and handle span the door. Guides, rod ends, e-clips and keepers in outdoor ice and dust add many failure points, so outdoor durability 6 is reduced to 5 and usability 7 to 6." ], "confidence": "low", "reviewer_notes": "Independent recalculation: rod force = 50 N x 80 mm / 8 mm x 0.7 = 350 N. Wedge factor for a 15 deg ramp is (1 - mu tan a)/(tan a + mu) = 1.62 at mu 0.3 and 2.30 at mu 0.15, as the analyst says. Door total 567-804 N. Per point: 2-point 283-402 N, 4-point 142-201 N at closing. Bearing: 4x8 mm pin at 5 / 8 / 10 / 22 MPa gives 160 / 256 / 320 / 704 N, and 5x10 mm at 8 MPa gives 400 N. Needed handle torque for 2.8 kN is about 14 N.m at mu 0.15 and about 20 N.m at mu 0.3. My typical of 150 N per point is 40 % below the analyst's 250 N, outside the 30 % tolerance, so it is corrected. The per-point sustained force is hand-limited, not bearing-limited. Fetched and confirmed: Magazine Industry (qualitative only, no span or latch-count data); CNC Kitchen threaded-insert page (numbers as quoted; test temperature and orientation not stated); CNC Kitchen ASA/PETG hook test (standing hooks 29 % / 46 % of lying); filamentspecs (PETG 11.5 % vs PLA 3 % preload loss, no conditions). GlobalSpec returned 403 for the analyst and I did not re-check it. The whole mechanism rests on first-principles estimates with no printed reference, so confidence is low.", "dead_or_misquoted_sources": [ "https://www.globalspec.com/ds/3851/areaspec/features_gasket was reported 403 by the analyst and I did not re-check it. Treat as unverified", "https://www.magazine-industry-usa.com/news/1936-getting-the-latch-and-hinge-specification-right is real but purely qualitative. It supports only 'multi-point latching exists for large spans', not any force or latch-count figure", "https://www.cnckitchen.com/blog/helicoils-threaded-insets-and-embedded-nuts-in-3d-prints-strength-amp-strength-assessment: the numbers are right, but the analyst's 'room temperature' label is an assumption (the page states no test temperature), and the data are pull-out values that do not apply to a pin-bearing load path", "https://filamentspecs.com/creep-resistance-3d-printed-parts/ is quoted correctly (11.5 % vs 3 %) but has no bolt, stress or temperature conditions, so it cannot support the 25-55 % loss range" ] } }, { "id": "double-throw-butterfly", "name": "Double-throw / butterfly recessed case latch (stamped steel)", "working_principle": "The Penn Elcom page calls this a recessed butterfly latch. The usual flight-case construction is a recessed dish with a spring-loaded folding or twist butterfly handle that engages a catch plate or keeper. The 'double-throw' label is the researchers', and neither the page nor my fetch confirms it. I analyse the printable principle as a quarter-turn cam draw, where a ramped cam or hook on the butterfly pulls the keeper down about 1.5 mm. A folding-lever over-centre reading has similar force limits. Commercial versions are 1.2 mm stamped steel with a steel spring, built for lid weight and shock, not gasket compression.", "mechanical_advantage": "Butterfly wing arm 18 mm / cam radius 8 mm = 2.25:1. The cam rises 1.5 mm per quarter turn (6 mm per revolution, lead angle 6.8 deg). With mu 0.3 the wedge factor is (1 - mu tan lam)/(tan lam + mu) = 2.3, so F_axial is about 5.2 x the finger force (155 N from 30 N). It is self-locking, since the 6.8 deg lead angle is below the 16.7 deg friction angle.", "peak_clamp_force_N": 400, "sustained_clamp_force_N": { "low": 70, "typical": 120, "high": 200 }, "limiting_factor": "First hand torque (~0.5 N.m of finger effort gives ~155 N), then tension creep in the thin printed hook arm (a 10x5 mm arm at 3-5 MPa and Kt 1.5 holds ~100-170 N). The latch has a fixed geometry with little or no adjustment and no hard stop, so the gasket squeeze depends on tolerances. The commercial 90 kg rating (~883 N) is a lid-holding working load for a 1.2 mm steel latch and not a gasket draw force, and a printed copy will not match it.", "force_basis": "calculated", "calculation": "Commercial anchor (verified by re-fetch): Penn Elcom medium MOL recessed butterfly latch L905/928PBZ, max working load 90 kg (~883 N), 1.2 mm steel, zinc finish, 105x102 mm, 13 mm dish. The page does not say twist or double-throw. Printed version, own calc. Finger force 30 N at 18 mm arm = 0.54 N.m. Cam radius 8 mm, 6 mm lead per revolution (lead angle 6.8 deg), mu = 0.3 for printed-on-steel. F_axial = F_hand x (18/8) x 2.3 = 5.2 F_hand = 155 N (103 N at 20 N finger force, 207 N at 40 N). Hook arm tension: 10x5 mm = 50 mm^2, sustained 3 / 4 / 5 MPa, Kt = 1.5 gives 100 / 133 / 167 N. A thinner 36 mm^2 arm at 4 MPa gives 96 N. With the lead's conservative bearing and hot-sun margin I set low 70 N, typical 120 N, high 200 N. Peak: 80 N finger force x 5.2 = 414 N, and wing bending at 80 N x 18 mm over a 12x5 mm section is ~29 MPa, near the ASA limit, so peak ~400 N. On the reference lid at 100 mm pitch, 120 N is 1.2 N/mm, below the 2-4 N/mm window, and 250 mm pitch would be needed to hit ~0.5 N/mm. Series stiffness: hook arm EA/L = 1800 x 50/25 = 3,600 N/mm against ~625 N/mm gasket stiffness per latch at 100 mm pitch (own calc, 6.25 N/mm^2 x 100 mm). Loss = 0.85 x set, i.e. 25-49 % force loss for a 30-58 % compression set. Evidence note: the WebSearch budget was exhausted in this run, so no printed-butterfly test data was found.", "operating_force_N": 30, "preload_retention": "Poor. The printed hook arm is stiff (3,600 N/mm vs ~625 N/mm gasket per latch), so ~85 % of the gasket compression set at 70 C (30-58 %) appears as force loss, 25-49 %. The geometry is fixed, so there is no way to retension unless the keeper is a screw. The cam is self-locking at rest, but vibration and thermal cycling plus creep of the contact surfaces can back it off.", "adjustable_preload": false, "positive_compression_stop": false, "scores": { "seal_suitability": 3, "outdoor_durability": 5, "printability": 6, "usability": 8 }, "best_materials": "Buy the stamped latch in stainless for outdoor use. Zinc-plated steel only gives 12-72 h salt spray and yellow zinc 96-120 h (albanycountyfasteners, from the lead). For printed parts use ASA for the wings, cam and recess, with a stainless pin and keeper. PC (UV-stabilised) for more creep margin. Not PETG at 60-70 C.", "hardware": "Stamped stainless (A2/A4) butterfly latch and keeper (buy), or for a printed copy a 4 mm stainless pin, stainless keeper screw or bar and a stainless spring.", "design_guidelines": [ "Use it as a secondary keeper or alignment aid beside a proper clamp. Do not use it as the primary clamp for a solid 85A TPU gasket.", "If printing a twist-cam version: cam radius ~8 mm, 6 mm per revolution lead (6-8 deg lead angle so it self-locks), quarter-turn stop, wing span 36-45 mm, hook arm >= 10x5 mm printed flat with the load in XY.", "Make the keeper an adjustable M4 stainless screw or bar so preload can be retensioned. Add a printed hard stop beside the latch at 0.75-0.8x the free bead height.", "Use a 4 mm stainless pin with bearing <= 8 MPa (4x8 mm = 32 mm^2 is good for ~250 N sustained). Pin axis along Z.", "Add a detent or spring so the butterfly cannot back out in vibration. Keep the recess drained.", "Fillets >= 1.5 mm on the hook and cam root. ASA has only ~3 kJ/m2 notched Charpy at -30 C.", "Place latches at the rim-bending pitch limit (~28 mm for a 3 mm flat lid edge, ~110 mm with a 20 mm skirt). Several latches of ~120 N are what the lid needs." ], "failure_modes": [ "Hook arm creep or fracture at 60-70 C", "Cam or wing wear and slip under vibration, so the latch backs out", "Wing breakage when over-torqued by hand (peak ~400 N)", "Gasket compression set loses 25-49 % of the force with no way to retension", "Zinc-plated steel corroding outdoors (96-120 h salt-spray class)", "Recess collecting water and debris", "FDM tolerance giving too little or too much squeeze" ], "existing_designs": [ { "title": "Penn Elcom medium MOL recessed butterfly latch L905/928PBZ (commercial steel reference, not printable)", "url": "https://translations.penn-elcom.com/medium-mol-recessed-latch-with-padlock-bracket-in-deep-dish-l905-928pbz", "note": "Verified: 90 kg max working load, 1.2 mm steel, zinc, 105x102 mm, padlockable. Page does not say twist or double-throw." } ], "sources": [ { "title": "Penn Elcom medium MOL recessed latch L905/928PBZ", "url": "https://translations.penn-elcom.com/medium-mol-recessed-latch-with-padlock-bracket-in-deep-dish-l905-928pbz", "note": "Verified by re-fetch: 90 kg working load, 1.2 mm steel, zinc finish, 10.5x10.2 cm, 13 mm dish, 231 g, listed as a butterfly latch with no double-throw wording." }, { "title": "Lee Spring: music wire versus stainless steel", "url": "https://www.leespring.com/music-wire-versus-stainless-steel", "note": "Verified: music wire rusts and tops out ~121 C; 302/304 stainless to ~288-316 C. Use stainless springs outdoors." }, { "title": "Albany County Fasteners: fastener materials and coatings guide", "url": "https://www.albanycountyfasteners.com/media/48/29/31/1764608481/fastener-materials-and-coatings-guide.pdf", "note": "From the lead (zinc plate 12-72 h and yellow zinc 96-120 h salt spray); not re-fetched." }, { "title": "CNC Kitchen: comparing PLA, PETG and ASA", "url": "https://www.cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament", "note": "Verified: standing vs lying hook strength (ASA 17 vs 57 kg); ASA softens 110 C." }, { "title": "CNC Kitchen: Prusament PC Blend review", "url": "https://www.cnckitchen.com/blog/prusament-pc-blend-review", "note": "Verified: PC Blend hooks 74 and 77 kg lying vs 22-35 kg standing, softens ~110 C, fails 125 C; no creep data." }, { "title": "filamentspecs: creep resistance of 3D printed parts", "url": "https://filamentspecs.com/creep-resistance-3d-printed-parts/", "note": "Verified: PETG joint lost ~11.5 % preload in 7 days vs ~3 % PLA." } ], "review": { "id": "double-throw-butterfly", "verdict": "corrected", "peak_clamp_force_N": 350, "sustained_clamp_force_N": { "low": 45, "typical": 85, "high": 150 }, "scores": { "seal_suitability": 3, "outdoor_durability": 4, "printability": 6, "usability": 7 }, "issues": [ "The mechanism identity is unverified. The Penn Elcom page (re-fetched) calls it a 'Recessed Butterfly Latch' and gives 1.2 mm steel, zinc finish, 105x102 mm, 13 mm dish, 231 g, 10 holes, and 'Maximum working load capacity: 90kg'. It does not say twist, cam or double-throw. The 'double-throw' label and the quarter-turn cam are the analyst's own model of a hypothetical printed latch. The 90 kg (883 N) figure is a lid-holding rating for a steel latch, correctly not used as a draw force.", "The wedge arithmetic reproduces: lead 6 mm/rev on r = 8 mm gives a 6.8 deg lead angle, wedge factor 2.30, gain 18/8 x 2.30 = 5.17, so 155 N from a 30 N finger. It ignores pivot friction. With a 4 mm pin at mu 0.3 the closing force is about 132 N. A pure cam is only about 27 % efficient.", "Hook-arm capacity is inconsistent with the snap-fit analysis. The 100 / 133 / 167 N figure for the 10x5 arm at 3 / 4 / 5 MPa and Kt 1.5 assumes zero eccentricity (e = 0). With the hook line offset e = 1 mm the arm holds 45 / 61 / 76 N (68 / 91 / 114 N without Kt). With e = 2 mm it holds 29-49 N. The arm therefore limits sustained force to about 60-90 N, below the 120 N typical.", "The latch is force-limited by the user's twist, not stroke-limited. At 132-155 N through the series stiffness (hook 3600 N/mm in series with 625 N/mm of gasket per 100 mm pitch) the gasket compresses only about 0.25-0.29 mm. The 1.5 mm cam throw is mostly consumed by FDM clearance. Clamp force therefore varies about +/-35 % with 20-40 N finger effort (103-207 N), and there is no stop or adjustment.", "Sustained = closing force x (1 - set loss). With 25-49 % loss (ks/(kg+ks) = 0.85) a 132-155 N closing force falls to 67-116 N. At 100 mm pitch this is 0.5-1.0 N/mm, below the 2 N/mm floor. Typical lowered from 120 to 85 N.", "Peak. 80 N finger x 18 mm x 2.3 gives 414 N. With pivot friction it is 350 N, and wing bending (12x5 mm) is 28.8 MPa, consistent. Peak set to 350 N.", "Outdoor durability. A zinc-plated stamped steel latch only has 12-72 h salt-spray class (yellow zinc 96-120 h) per the analyst's Albany source, which I could not read. A printed cam under 100 N at 60 C will creep and wear, with back-out in vibration unless a detent holds it. The recess collects water. Durability 5 reduced to 4. Usability 8 reduced to 7 because the twist effort sets the preload." ], "confidence": "low", "reviewer_notes": "Independent recalculation: lead angle = atan(6 / (2 pi 8)) = 6.81 deg; wedge (1 - mu tan l)/(tan l + mu) = 2.299 at mu 0.3; efficiency tan l x wedge = 0.274; gain 2.25 x 2.299 = 5.17. F = 103 / 155 / 207 N at 20 / 30 / 40 N finger force, 414 N at 80 N. Including 4 mm pin friction (mu 0.3) the closing force at 30 N is 132 N. Hook arm 10x5 mm: factor 1 + 6e/t = 1 / 2.2 / 3.4 at e = 0 / 1 / 2 mm. Capacity at 4 MPa with Kt 1.5 is 133 / 61 / 39 N. Series fraction 3600/(3600+625) = 0.852, so loss is 0.85 x 30-58 % = 25-49 %. Sustained is therefore about 66-116 N from the closing force and about 60-90 N from the arm at e of about 1 mm. Typical 85 N is 29 % below the analyst's 120 N. I used 'corrected' because the arm capacity ignores eccentricity and the model is not the cited product. Fetched and confirmed: Penn Elcom (90 kg working load, 1.2 mm steel, zinc, 105x102 mm, 13 mm dish, no 'twist' or 'double-throw' wording); Lee Spring (music wire strength drops above about 121 C, rusts when wet; stainless superior outdoors); CNC Kitchen hook test; CNC Kitchen PC Blend review not re-fetched by me. The Albany fastener guide PDF text could not be extracted by my fetch, so the salt-spray hours (12-72 h, 96-120 h) are unverified by me. The WebSearch budget was exhausted, so I could not look for the real meaning of 'double-throw' or for printed butterfly or cam latch tests.", "dead_or_misquoted_sources": [ "https://translations.penn-elcom.com/medium-mol-recessed-latch-with-padlock-bracket-in-deep-dish-l905-928pbz is quoted correctly (90 kg working load, 1.2 mm steel, zinc) but never says 'double-throw' or twist. The 'double-throw' naming is unsupported", "https://www.albanycountyfasteners.com/media/48/29/31/1764608481/fastener-materials-and-coatings-guide.pdf: the salt-spray hours (12-72 h zinc, 96-120 h yellow zinc) could not be read by my fetch and are unverified", "https://www.leespring.com/music-wire-versus-stainless-steel: the 121 C limit for music wire is right, but the 288-316 C figure is a general stainless range, not stated for 302/304, and '25-30 % weaker' is the analyst's derivation, not a page statement", "https://www.cnckitchen.com/blog/prusament-pc-blend-review was not re-fetched by me; the PC Blend hook numbers (74 / 77 kg lying, 22-35 kg standing) are unverified in this review" ] } } ], "calibration": { "ranking_by_clamp_force": [ { "id": "perimeter-band-clamp", "rank": 1, "sustained_clamp_force_N_typical": 800, "one_line_verdict": "Highest number but it is a whole-closure force for one steel band on a ROUND or oval lid (about 2.1 N/mm on a 377 mm path), not a per-latch force. It does not fit the 70x35x30 mm envelope or the 200x150 mm rectangle. A 10x8 mm printed ring and a spring in the T-bolt are required." }, { "id": "cam-lever-steel-stud", "rank": 2, "sustained_clamp_force_N_typical": 350, "one_line_verdict": "Highest true per-latch force. Limits are the M5 pin bearing in 2x7 mm ears and the insert anchor in a thick ledge. A steel stud, plate and spring stack are mandatory, so it is a hybrid with a printed lever and bracket. Adjustable, with a positive stop and about 25 N hand force." }, { "id": "swing-bolt-wing-nut", "rank": 3, "sustained_clamp_force_N_typical": 300, "one_line_verdict": "Cut from 400 N because the clevis bracket anchors to the wall like a baseline screw and adds a pin joint. Torque is set by the hand, so a Belleville stack or torque-limiting knob is needed. Fully re-tensionable, but slow to operate." }, { "id": "baseline-screws", "rank": 4, "sustained_clamp_force_N_typical": 250, "one_line_verdict": "The benchmark any printed latch must beat. Limited by insert pull-out and the washer seat in a hot boss. Durable and printable, with an inherent stop, but rigid, so 35-55 % of the force is lost after hot sun until re-tightened. Usability 3." }, { "id": "captive-screw-spring-stack", "rank": 5, "sustained_clamp_force_N_typical": 220, "one_line_verdict": "Same boss limit as the baseline, slightly lower because a spring holds the load continuously. Best retention of the screw types (calculated about 85-95 % held after hot set, not validated) and removes most of the cold overload. Needs a die spring or Belleville stack, not a small coil." }, { "id": "vise-action-screw-cam", "rank": 6, "sustained_clamp_force_N_typical": 200, "one_line_verdict": "Limited by the keeper ledge loaded across layers (120-240 N). Adjustable, with a positive stop and about 22 N hand force. Printed helical ramps wear. Force scatter is about 40 % without a spring." }, { "id": "oc-adjustable-screw-hook", "rank": 7, "sustained_clamp_force_N_typical": 185, "one_line_verdict": "Over-center lever with a steel eye-bolt adjuster. About five printed failure modes (wall bearing, pin bores, lug, ear root, keeper) sit within about 1.4x of each other. Re-tensionable (0.2 turn restores hot-set loss) and quick to operate. A rigid link, so scheduled re-tensioning is required." }, { "id": "oc-spring-loaded-compensating", "rank": 8, "sustained_clamp_force_N_typical": 170, "one_line_verdict": "Same printed limits as the screw-hook version, minus a knock-down for the carriage and guides. Best end-of-life retention of the over-center types (about 92 % kept). Fit in the envelope is unproven, and the exposed spring and guide are weak outdoors." }, { "id": "threaded-lid-cap", "rank": 9, "sustained_clamp_force_N_typical": 165, "one_line_verdict": "Round caps of 50 mm or less only. Force is torque-limited (about 3 Nm drives about 165 N because TPU face drag dominates). Thread-root bending across layers caps the structure near 400 N, not 1 kN. About 1 N/mm on the 157 mm ring, below the 2-4 N/mm window." }, { "id": "quarter-turn-compression", "rank": 10, "sustained_clamp_force_N_typical": 150, "one_line_verdict": "A printed pawl alone gives about 115 N. 150-350 N needs a steel pawl and a keeper. Commercial 4-6 mm ramp travel does not match the 0.5 mm gasket stroke, so force scatter is about 40 %. Better with foam or a thin rib than with the 85A design rib." }, { "id": "multi-point-rod-latch", "rank": 11, "sustained_clamp_force_N_typical": 150, "one_line_verdict": "This is per latch POINT on a 4-point door. One handle delivers only about 0.57-0.8 kN in total before set loss, which is 0.5-1.1 N/mm. It does not fit the envelope. Rod, bellcrank and guide complexity outdoors hurts durability." }, { "id": "wedge-slide-bolt", "rank": 12, "sustained_clamp_force_N_typical": 140, "one_line_verdict": "Cut from 200 N to the force a reasonable push can deliver. The wedge gives excellent stroke control (10:1) and recovers hot set, but it needs a separate pivoted tab or catch block anchor. Loose wedge, fretting and ice jams are the risks." }, { "id": "bayonet-twist-lock", "rank": 13, "sustained_clamp_force_N_typical": 120, "one_line_verdict": "Round lids only. Torque and TPU drag give 92-183 N at 2-4 Nm, and the lug roots across layers give 120-180 N. Fixed ramp height, no re-tightening, 30-58 % hot loss. About 0.7 N/mm, so it suits only small lids." }, { "id": "oc-fixed-hook-pinned", "rank": 14, "sustained_clamp_force_N_typical": 85, "one_line_verdict": "Cut from 110 N. The printed claw throat is a curved-beam limit of about 40-70 N, with a bent A4 wire hook the only route to 100 N or more. No adjustment, so +/-0.3 mm of tolerance is +/-160 N. After hot set the line load falls to about 1 N/mm or less." }, { "id": "double-throw-butterfly", "rank": 15, "sustained_clamp_force_N_typical": 65, "one_line_verdict": "The printed hook arm with 1 mm of load eccentricity holds about 45-76 N. The 90 kg figure belongs to a stamped steel latch and is not a gasket force. No stop or adjustment, and closing force depends on the finger. Cut from 85 N." }, { "id": "rotary-cam-lock-simple", "rank": 16, "sustained_clamp_force_N_typical": 60, "one_line_verdict": "The thumb can overload the printed tongue (165-225 N at 0.8 Nm). The tongue limits it to about 25-100 N. No stop, and no way to re-tighten. A 700 mm path would need 15-35 cams." }, { "id": "cam-hook-printed", "rank": 17, "sustained_clamp_force_N_typical": 55, "one_line_verdict": "Hook jaw root limited (Winkler curved beam, about 0.075-0.115 MPa/N). Fixed stroke, no spring, and the +/-0.2 mm of FDM tolerance is +/-40-100 % of the force. Fine on small boxes with a light rib. Hot creep takes 40-70 % of the force." }, { "id": "bail-wire-latch", "rank": 18, "sustained_clamp_force_N_typical": 50, "one_line_verdict": "The wire (steel) is not the limit. The printed catch hook is (about 7 MPa at 60 N). Good retention because the wire acts as the spring. 28-56 latches would be needed on the reference lid." }, { "id": "oc-fully-printed", "rank": 19, "sustained_clamp_force_N_typical": 40, "one_line_verdict": "Printed posts loaded across layers and C-hook creep limit it (post bending 25-34 N for a 9 mm post standing). Print-in-place posts reach only about 10 N. About 0.46 N/mm with 8 latches. No steel to fix it." }, { "id": "snap-fit-compliant", "rank": 20, "sustained_clamp_force_N_typical": 18, "one_line_verdict": "A rigid snap hook holds about 9-25 N and cannot store preload. The 85A design rib pushes back about 84 N per hook. A TPU strap holds more but relaxes. Useful only as a position keeper beside a real clamp." } ], "best_for_outdoor_tpu_seal": [ { "id": "cam-lever-steel-stud", "rank": 1, "why": "Highest sustained force of any per-latch mechanism that stays adjustable (about 350 N, range 220-550). With 6-8 latches this covers the 1.4-2.8 kN window, and it has a positive stop, a steel stud and plate, and low hand effort (about 25 N). It must have a Belleville or spring stack under the setting nut (about 4x softer than the gasket) to cut 85A set loss from 30-58 % to about 10 % and to cap the cold overload. Also needs an A4 stud, pin and plate, and a stiffened rim. Confidence low; 1-week 65 C force-gauge soak required." }, { "id": "swing-bolt-wing-nut", "rank": 2, "why": "About 300 N sustained (range 200-450). A steel eye-bolt with a washer or Belleville stack gives the highest force among the fully recoverable closures, and it can be re-tightened after the first hot week. Use an A2/A4 DIN 444 bolt, not the zinc 4.6 version. Print the clevis flat as a separate bracket, because an integral upright clevis tears at about 340 N or less. Limit torque with a small knob or slip clutch. Usability 4 (several turns each)." }, { "id": "captive-screw-spring-stack", "rank": 3, "why": "About 220 N (range 110-380) on the simplest printed geometry (boss, insert, washer). The spring stack gives the best calculated retention (about 83-96 % after hot set, unvalidated) and avoids the +100 % cold overload of a rigid screw. Add a printed or steel-sleeve hard stop. Needs a die spring or Belleville stack, since a coil spring light enough to help is impractical. About 11 mm thread depth; usability 4." }, { "id": "oc-adjustable-screw-hook", "rank": 4, "why": "About 185 N (range 130-240) with the best operability of the lever types (about 10 N hand force, one motion). A steel eye-bolt re-tensions (about 0.2 turn restores a 37 % hot-set loss). Six to eight latches give about 1.9-2.6 N/mm, the bottom of the design window. Rigid, so expect to re-tension after the first hot weeks. Fit a locknut and a printed hard stop." }, { "id": "oc-spring-loaded-compensating", "rank": 5, "why": "About 170 N (range 120-220), but it keeps about 92 % of its preload after hot set (rigid latches keep about 63 %) and the cold rise is only about 10 %. Needs 8 or more latches to reach the lower window edge. Printability 6, exposed spring and sliding carriage lower durability to 5, and fit in 70x35x30 mm is not demonstrated. A steel stop is needed so the spring cannot coil-bind." }, { "id": "perimeter-band-clamp", "rank": 6, "why": "Conditional on a ROUND or oval lid of about 100-200 mm. About 800 N per closure (about 2.1 N/mm on a 120 mm lid), with a uniform line load that removes the rim-bending pitch problem. Use a stainless band, 10x8 mm or metal-reinforced rings, and a spring in the T-bolt. Not a per-latch number and not usable on a rectangular lid. For round lids it would rank near the top." }, { "id": "baseline-screws", "rank": 7, "why": "Reference to beat, not a latch: about 250 N per screw with the best durability (8) and printability (9) and an inherent stop. Rigid, so 35-74 % of the force is lost in hot sun until re-tightened, and cold raises the force about 2x. A steel compression sleeve and a spring washer or stack are the cheap upgrades. Usability 3 (6-11 screws)." }, { "id": "vise-action-screw-cam", "rank": 8, "why": "About 200 N (range 100-350), adjustable by the stud nut, with a positive stop and about 22 N hand force. Limited by the keeper ledge across layers, and printed ramps wear and back-drive under ice or dirt. Needs a wave spring or Belleville plus a 2.5-3 mm ramp rise to hold the force. Only worthwhile with a steel keeper." }, { "id": "wedge-slide-bolt", "rank": 9, "why": "About 140 N (range 75-280) hand-limited, but the best stroke control of the non-screw types: 1 mm of squeeze needs 10 mm of travel, so tolerance and hot set are easy to take up. A jack screw raises it to 250-300 N. Anchoring the tab and catch block is the real limit. Loose wedge, fretting and ice jams hurt outdoor durability (5)." }, { "id": "quarter-turn-compression", "rank": 10, "why": "About 150 N (range 60-300) and only with a steel pawl and keeper, since a printed pawl holds about 115 N. Convenient and has a positive stop, but 4-6 mm commercial travel against a 0.5 mm gasket stroke gives about +/-40 % force scatter. Better suited to foam or a thin rib than the 85A design rib; included to fill the top 10, not as a recommendation." } ], "adjustments": [ { "id": "swing-bolt-wing-nut", "field": "sustained_N.typical", "from": "400 (reviewer; range 250-600)", "to": "300 (range 200-450)", "reason": "The clevis must be a separate bracket anchored by screws or inserts into a 3-4 mm wall (the reviewer's own text says this has not been shown to carry 500 N hot), so it shares the baseline-screw anchor limit and adds a pin joint plus a slot seat across layers. It cannot exceed baseline-screws (250 N) by 1.6x. 300 N is the baseline scaled by about 1.2 for the larger M5 hardware, and it ranks below the cam lever, whose stud anchors in an M5 insert in a thick ledge." }, { "id": "wedge-slide-bolt", "field": "sustained_N.typical", "from": "200 (reviewer; range 100-400)", "to": "140 (range 75-280)", "reason": "Same hand-limited rule as the cap and bayonet: input at or near the 50 N comfort limit. The reviewer's own 1.64-2.48 push ratio gives 82-124 N from 50 N, so 200 N needs 80-125 N of push. The catch block is also a cantilever loaded across layers, as in the vise-action latch." }, { "id": "double-throw-butterfly", "field": "sustained_N.typical", "from": "85 (reviewer; range 45-150)", "to": "65 (range 40-120)", "reason": "The reviewer deducted gasket set loss from a hand-limited closer, which the cap, bayonet and multi-point reviews did not do, so that deduction was inconsistent. The structural limit is the 10x5 mm hook arm with 1 mm of eccentricity (45-76 N at 3-5 MPa with Kt 1.5), the same hook-arm limit as the cam-hook (55 N) and bail (50 N). Typical set to the arm limit." }, { "id": "oc-fixed-hook-pinned", "field": "sustained_N.typical", "from": "110 (reviewer; range 70-150)", "to": "85 (range 50-130)", "reason": "The analyst's neck check puts the load line 3 mm off the neck centre line on a straight beam. A real claw throat (inner radius about 2 mm, load line through the centre of curvature) gives about 0.10 MPa/N by the Winkler method used for the cam-hook and bail reviews, which is about 40-70 N at 4-7 MPa. The reviewer's 110 N credits an unmodelled bent-wire hook; set to a blend of the printed claw and the wire variant." }, { "id": "perimeter-band-clamp", "field": "comparability basis", "from": "per latch", "to": "per closure (one T-bolt band, round or oval lid, about 377 mm path)", "reason": "The 800 N figure is the axial force of the whole band on a 120 mm round lid. Every other entry is per latch device on a rectangular lid. Value unchanged, but it is flagged as not directly comparable and excluded from the rectangular-lid recommendation." }, { "id": "threaded-lid-cap", "field": "comparability basis", "from": "per latch", "to": "per closure (single round cap, 50 mm or less)", "reason": "One cap carries the whole 157 mm ring, and torque scales as diameter squared, so the figure does not extend to larger lids. Value unchanged (165 N); ranked on the number but not offered as a rectangular-lid latch." } ], "methodology_notes": "Common basis used: sustained force = the lower of (a) the printed-structure capacity at the working allowables for ASA at 60-70 C (in-plane 3 / 4 / 5.5 MPa, pin bearing 6 / 8 / 10 MPa, across layers about 2 MPa, with stress-concentration factors where a reviewer applied them) and (b) the force a hand can deliver at about 20-50 N finger force or 3-4 N.m torque. Gasket set, creep and cold are reported as retention and are not subtracted, so a rigid latch's number is its as-set capacity and about 55-65 % of it remains after the first hot weeks (loss = set x k_latch/(k_latch + k_gasket), own calc). The Texin 985 gasket numbers (https://sushengpolymer.com/media/pdf/phFiH7_Texin-985.pdf) give 2.2x flexural modulus at -30 C, so a fixed-stroke latch sees up to 1.5-2x the force in the cold. The ASA hook anisotropy (lying 57 kg vs standing 17 kg, https://www.cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament) and the M3 insert pull-out (about 1.17 kN, PETG, 23 C, short term, https://www.cnckitchen.com/blog/helicoils-threaded-insets-and-embedded-nuts-in-3d-prints-strength-amp-strength-assessment) are the only measured anchors. The hand-force and friction values come from https://elesa.com/en/elesab2bstoreca/Clamping-handles--Cam-levers--GN9272-A--d1. All other values are reviewers' or my own calculations. I found no printed sustained-load test for any mechanism, so every number is a calculation or estimate, and the ASA allowables themselves are an untested working rule, so expect +/-2x on absolute values (the ranking is more robust than the numbers). Where mounting choices differed between reviewers (4 mm pins vs M5 pins, thin wall vs thick boss), differences of about 20 % were left alone, and only larger or logically inconsistent gaps were adjusted. Peak values from the reviews (roughly 2.5-6x sustained) are room-temperature breaking estimates and were not used for the ranking. Two entries are closure-level, not per latch (perimeter band, threaded cap), and one is per latch point (multi-point rod). Material effects: PC (UV-stabilised grade only) could raise the structure-limited values about 1.3-1.5x (own judgement), but not the hand-limited or steel-limited ones. PETG and PETG-CF sit at their HDT at 60-70 C and are not suited to sustained load. PA6-CF loses about 22 % strength to moisture and should be avoided outdoors; PAHT-CF is acceptable but still creeps. Largest uncertainties: ASA hot creep allowables, anchor pull-out hot and sustained, printed-bead stiffness (+/-2x), and rim bending, since the latch count is limited by rim stiffness (about 28 mm pitch on a flat 3 mm edge, about 110 mm with a 20 mm skirt) before latch strength.", "headline_recommendation": "For a TPU 85A seal on a rectangular outdoor lid, no purely printed latch comes close. The best-supported choice is a steel-assisted, adjustable clamp with a series spring and a printed hard stop: a cam lever on an A4 stud (about 350 N sustained each), or a swing eye-bolt or captive screw with a Belleville stack (about 220-300 N), with 6-8 latches round a stiffened rim and the 1.2-1.6 mm design rib at 2-4 N/mm. All-plastic snap, bail, cam-hook and over-center latches hold only about 20-85 N sustained and cannot hold that rib. For round lids a V-band clamp delivers about 800 N per closure. Verify every design with a force-gauge test and a 65 C soak, since the numbers are +/-2x." }, "missing": [] }