{"$schema":"nativecad-dfm-pack/1","id":"load-driven-detailing","title":"Load-driven detailing: rotating bodies, castings and fabricated frames","sector":"load-driven-detailing","version":"2026-10-23","summary":"Cited rules for taking material out of gear/pulley/sprocket bodies, castings and fabricated frames the way engineered parts are: rim backup ratio, web, hub, lightening holes, cast wall/draft/rib/boss, rail taper and flanged holes.","aliases":["load-driven detailing","load-driven design","lightening holes","material removal","gear web","gear rim","backup ratio","cast ribs","cast wall thickness","ladder frame","chassis rail","pulley body","flanged lightening hole"],"crossSector":false,"size":"core","sources":[{"id":"agma-2001-d04","title":"ANSI/AGMA 2001-D04 Fundamental rating factors and calculation methods for involute spur and helical gear teeth (rim thickness factor K_B)","accessed":"2026-10-23"},{"id":"iso-6336-3","title":"ISO 6336-3 Calculation of load capacity of spur and helical gears, Part 3: tooth bending strength (rim factor Y_B)","accessed":"2026-10-23"},{"id":"shigley-ch14","title":"Budynas & Nisbett, Shigleys Mechanical Engineering Design, ch. 14 (AGMA bending, K_B, backup ratio m_B)","url":"https://highered.mheducation.com/sites/dl/free/9814595284/1054140/Budynas_Chapter_14.pdf","accessed":"2026-10-23"},{"id":"iastate-me325","title":"Iowa State ME 325 handout: bending stress in gears (K_B piecewise form)","url":"https://engineering.iastate.edu/~gkstarns/me325/bending_stress_gears.pdf","accessed":"2026-10-23"},{"id":"iso-53","title":"ISO 53 Cylindrical gears for general and heavy engineering: standard basic rack tooth profile (ha = 1.0 m, hf = 1.25 m)","accessed":"2026-10-23"},{"id":"machinerys-handbook","title":"Machinerys Handbook (Industrial Press): gear, flywheel and key/keyseat sections","accessed":"2026-10-23"},{"id":"dudley-gear","title":"Dudley, Handbook of Practical Gear Design (CRC Press): gear blank, web and hub proportions","accessed":"2026-10-23"},{"id":"bralla-dfm","title":"Bralla, Design for Manufacturability Handbook, 2nd ed. (McGraw-Hill), casting chapters","accessed":"2026-10-23"},{"id":"nadca-pss","title":"NADCA Product Specification Standards for Die Castings (wall, draft, rib, boss guidance)","accessed":"2026-10-23"},{"id":"asm-hbk-15","title":"ASM Handbook Vol. 15 Casting (design of castings, section modulus, gating)","accessed":"2026-10-23"},{"id":"campbell-casting","title":"Campbell, Complete Casting Handbook (Chvorinov solidification rule, hot spots)","accessed":"2026-10-23"},{"id":"engineersedge-sand","title":"Engineers Edge: design for sand casting (minimum wall, draft, section change)","url":"https://www.engineersedge.com/sand_cast.htm","accessed":"2026-10-23"},{"id":"giessereilexikon-design","title":"Giessereilexikon: favorable casting design (fillet radius a third to a quarter of wall; hot spots at re-entrant angles)","url":"https://www.giessereilexikon.com/en/foundry-lexicon/Encyclopedia/show/favorable-casting-design-4660/","accessed":"2026-10-23"},{"id":"xometry-diecast","title":"Xometry die casting design guide (rib thickness, draft, boss coring)","url":"https://xometry.com/resources/design-guides/die-casting-design-guide/","accessed":"2026-10-23"},{"id":"niu-airframe","title":"Niu, Airframe Stress Analysis and Sizing: lightening holes in webs, flanged holes","accessed":"2026-10-23"},{"id":"peterson-kt","title":"Pilkey, Petersons Stress Concentration Factors (hole in plate: Kt = 3.0 infinite plate, uniaxial tension)","accessed":"2026-10-23"},{"id":"roark","title":"Young & Budynas, Roarks Formulas for Stress and Strain: beams, uniform-strength sections, shear","accessed":"2026-10-23"},{"id":"blodgett-weldments","title":"Blodgett, Design of Weldments (Lincoln Electric): distortion, HAZ, joint detailing","accessed":"2026-10-23"},{"id":"aws-d1-1","title":"AWS D1.1 Structural Welding Code - Steel (weld detailing, gusset and fatigue categories)","accessed":"2026-10-23"}],"entries":[{"id":"ldd-rim-backup-ratio","kind":"rule","tier":1,"title":"Rim backup ratio m_B = t_R / h_t","summary":"Backup ratio m_B = rim thickness under the tooth root t_R divided by whole tooth depth h_t (2.25 m for the ISO 53 rack). Compute it before drilling anything in a gear body: every rim cut is checked against it.","applies":["gear","rim"],"basis":"SRC: AGMA 2001 / Shigley ch.14 define m_B = t_R/h_t; ISO 53 gives h_t = 1.0 m + 1.25 m.","sources":["agma-2001-d04","shigley-ch14","iso-53"],"tags":["backup-ratio","rim","gear"],"value":{"value":"m_B = t_R / h_t, h_t = 2.25 m","unit":"ratio"}},{"id":"ldd-rim-factor-kb","kind":"rule","tier":1,"title":"Rim thickness factor K_B (AGMA 2001) for thin rims","summary":"K_B = 1.0 for m_B >= 1.2; K_B = 1.6 ln(2.242 / m_B) for m_B < 1.2 (1.29 at m_B 1.0, 2.40 at 0.5). Multiplies tooth bending stress. Continuous at 1.2. Covered range 0.5 <= m_B; external gears.","applies":["gear","rim","lightened gear"],"basis":"SRC: textbook piecewise form (Shigley 14); ISO 6336-3 carries an equivalent Y_B. Check constants against the purchased standard.","sources":["agma-2001-d04","iso-6336-3","shigley-ch14","iastate-me325"],"tags":["kb","rim-factor","bending"],"value":{"table":[{"m_B":1.2,"K_B":1},{"m_B":1,"K_B":1.29},{"m_B":0.8,"K_B":1.65},{"m_B":0.6,"K_B":2.11},{"m_B":0.5,"K_B":2.4}]}},{"id":"ldd-rim-min-thickness","kind":"dimension","tier":1,"title":"Rim thickness for K_B = 1.0","summary":"Keep t_R >= 1.2 h_t = 2.7 m under the root so K_B = 1.0 (m=2: 5.4 mm; m=3: 8.1 mm). Thinner is allowed only down to m_B 0.5 with the K_B penalty on the bending check.","applies":["gear","rim"],"basis":"SRC: 1.2 x 2.25 m from the m_B >= 1.2 knee of K_B.","sources":["agma-2001-d04","iso-53"],"tags":["rim","module"],"value":{"min":2.7,"typical":2.7,"unit":"ratio"}},{"id":"ldd-web-thickness","kind":"rule","tier":1,"title":"Web thickness against face width","summary":"Web thickness t_W = 0.25 to 0.40 of face width F, and not less than half the rim thickness t_R. A thin web is limited by stiffness and tooth alignment, not shear, so verify deflection with FEA before going thinner.","applies":["gear","web"],"basis":"EST: handbook proportion (Dudley) for webbed gear blanks; strength is rarely the limit, rim deflection is. Verify by cad_fea_run.","sources":["dudley-gear","machinerys-handbook"],"tags":["web","face-width"],"value":{"min":0.25,"max":0.4,"typical":0.3,"unit":"ratio"}},{"id":"ldd-hub-od","kind":"dimension","tier":1,"title":"Hub OD against bore","summary":"Hub OD = 1.6 to 2.0 x bore for a keyed steel hub (1.8 to 2.2 x for cast iron or aluminium). The wall left under the keyseat must still carry the key bearing load.","applies":["gear","timing pulley","chain sprocket","idler","flywheel"],"basis":"EST: common handbook proportion; keyseat depth from Machinerys Handbook key tables.","sources":["machinerys-handbook","dudley-gear"],"tags":["hub","bore"],"value":{"min":1.6,"max":2,"typical":1.8,"unit":"ratio"}},{"id":"ldd-lighten-ligaments","kind":"rule","tier":1,"title":"Lightening-hole ligaments to rim, hub and each other","summary":"Leave a ligament >= max(t_W, 4 mm) from each hole to the rim inner face and to the hub OD, and >= max(1.5 t_W, 6 mm) between neighbouring holes. This keeps the rim at its t_R and the hub wall intact.","applies":["gear","pulley","flywheel"],"basis":"EST: ligament >= web thickness so no hole edge is thinner than the web it sits in.","sources":["dudley-gear","niu-airframe"],"tags":["ligament","lightening-hole"],"value":{"min":1,"unit":"ratio"}},{"id":"ldd-when-solid","kind":"rule","tier":1,"title":"When a rotating body stays solid","summary":"Keep the blank solid when (root radius - hub OD/2) < t_R + 2 x ligament + 6 mm: no hole fits that respects both ligaments. For m=2 that is roughly any gear under about 40 teeth on a 25 mm bore.","applies":["small gear","pinion"],"basis":"EST: geometric consequence of the ligament and rim rules; the 6 mm minimum drillable hole is the floor.","sources":["dudley-gear","agma-2001-d04"],"tags":["solid","pinion"],"value":{"min":6,"unit":"mm"}},{"id":"ldd-cast-wall-sand-al","kind":"dimension","tier":1,"title":"Sand-cast aluminium nominal wall","summary":"Nominal wall 4 to 8 mm by size (minimum 2.5 mm, 0.10 in, for small areas); keep every wall within +-25 percent of nominal so solidification stays directional.","applies":["sand casting","aluminium casting","gearbox case"],"basis":"SRC: 0.10 in minimum for aluminium sand castings (Engineers Edge); size bands EST from Bralla.","sources":["engineersedge-sand","bralla-dfm"],"tags":["wall","sand"],"value":{"min":4,"max":8,"typical":5,"unit":"mm"}},{"id":"ldd-cast-draft","kind":"dimension","tier":1,"title":"Draft by casting process","summary":"Draft per side: sand 1 to 3 deg (2 standard, 1 minimum); permanent mould 2 to 3 deg; HPDC 1 deg outside, 1.5 to 3 deg inside and on deep cores. Add draft to every face parallel to the pull, ribs and bosses included.","applies":["sand casting","permanent mould casting","die casting","grey iron","ductile iron"],"basis":"SRC: sand figures from Engineers Edge; die-cast figures from the Xometry/NADCA guide; PM EST.","sources":["engineersedge-sand","xometry-diecast","nadca-pss"],"tags":["draft"],"value":{"table":[{"process":"sand","min_deg":1,"typical_deg":2,"max_deg":3},{"process":"permanent mould","min_deg":2,"max_deg":3},{"process":"HPDC outside","min_deg":1},{"process":"HPDC inside","min_deg":1.5,"max_deg":3}]},"see":["automotive/diecast-draft-angle","consumer/draft-angle-minimum"]},{"id":"ldd-cast-rib-thickness","kind":"rule","tier":1,"title":"Rib thickness against wall","summary":"Rib root thickness 0.6 to 0.8 x wall in sand and iron, 0.4 to 0.6 x wall in die-cast aluminium; a rib as thick as the wall makes a hot spot and a sink at the root.","applies":["sand casting","permanent mould casting","die casting","grey iron","ductile iron"],"basis":"SRC: 40 to 60 percent (die casting, Xometry); sand/iron band EST from the same hot-spot logic (Campbell).","sources":["xometry-diecast","campbell-casting","bralla-dfm"],"tags":["rib"],"value":{"min":0.4,"max":0.8,"unit":"ratio"},"see":["automotive/diecast-rib-thickness-ratio"]},{"id":"ldd-cast-boss-od","kind":"dimension","tier":1,"title":"Boss OD at a bolt","summary":"Boss OD = 2.0 to 2.5 x thread diameter (M10: 20 to 25 mm); core out the middle so the boss wall equals the nominal wall, and give the tapped hole at least 1 x d of thread engagement in aluminium.","applies":["bolt boss","bolted flange"],"basis":"EST: handbook proportion; coring to keep a uniform wall is the die-cast practice (Xometry guide).","sources":["xometry-diecast","bralla-dfm"],"tags":["boss","bolt"],"value":{"min":2,"max":2.5,"typical":2.2,"unit":"ratio"}},{"id":"ldd-cast-fillet-radius","kind":"rule","tier":1,"title":"Inside fillet radius at every junction","summary":"Inside fillet R = 0.25 to 0.33 x wall (a quarter to a third); the outside radius = inside R + wall so the section stays constant round the corner. Too large a fillet makes a hot spot of its own.","applies":["sand casting","permanent mould casting","die casting","grey iron","ductile iron"],"basis":"SRC: Giessereilexikon (quarter to a third of wall); outside = inside + wall is the constant-section rule (Bralla).","sources":["giessereilexikon-design","bralla-dfm"],"tags":["fillet","corner"],"value":{"min":0.25,"max":0.33,"unit":"ratio"}},{"id":"ldd-cast-hotspot-junction","kind":"rule","tier":1,"title":"Hot spots at junctions","summary":"Solidification time scales with (volume / cooling area)^2 (Chvorinov). Keep the largest circle inscribed at an L, T or X junction <= 1.25 x wall, and stagger ribs so no four-way crossing remains.","applies":["sand casting","permanent mould casting","die casting","grey iron","ductile iron"],"basis":"SRC: Chvorinov rule (Campbell); the 1.25 x inscribed-circle limit is EST design practice.","sources":["campbell-casting","asm-hbk-15"],"tags":["hot-spot","junction","chvorinov"],"value":{"max":1.25,"unit":"ratio"}},{"id":"ldd-rail-taper-moment","kind":"rule","tier":1,"title":"Rail depth follows the bending moment","summary":"For constant stress at fixed width, section modulus follows M(x): depth h ~ sqrt(M). Cantilever end load (M ~ x) gives a parabolic taper, uniform load (M ~ x^2) a straight linear taper. Depth tracks the moment, not the length.","applies":["ladder frame","chassis rail","fabricated frame","plate"],"basis":"SRC: beam of uniform strength (Roark; Shigley ch.3), h = sqrt(6 M / (b sigma)).","sources":["roark"],"tags":["taper","moment","rail"],"value":{"value":"h(x) = sqrt(6 M(x) / (b sigma_allow))","unit":"ratio"}},{"id":"ldd-hole-dia-vs-web","kind":"rule","tier":1,"title":"Lightening-hole diameter against web depth","summary":"Unflanged hole diameter <= 0.5 to 0.6 x web depth at that station; flanged hole up to 0.8 x web depth. The hole sits on the neutral axis, in low-shear mid-span, never within one web depth of a support or load point.","applies":["ladder frame","chassis rail","fabricated frame","plate"],"basis":"EST: airframe practice (Niu, lightening holes in webs); limits come from shear buckling of the strip left above and below.","sources":["niu-airframe","roark"],"tags":["lightening-hole","web"],"value":{"min":0.5,"max":0.8,"unit":"ratio"}},{"id":"ldd-hole-kt","kind":"rule","tier":1,"title":"Stress concentration of a hole","summary":"A circular hole in a wide plate under tension has Kt = 3.0 (4.0 in pure shear): the edge sees three times nominal stress. Put holes where nominal stress is under a third of allowable, near the neutral axis, with slot corners at R >= 1 x plate thickness.","applies":["ladder frame","chassis rail","fabricated frame","plate"],"basis":"SRC: Peterson Kt for a circular hole, infinite plate (3.0); slot corner radius EST.","sources":["peterson-kt"],"tags":["kt","hole","stress-concentration"],"value":{"value":3,"unit":"ratio"}},{"id":"ldd-gusset-crossmember","kind":"rule","tier":1,"title":"Gussets at crossmember joints","summary":"Gusset thickness >= 0.8 x joined member wall, leg length >= 1.5 x member depth, 45 deg bias, with a corner scallop R >= 20 mm so welds never cross. Use where a crossmember meets a rail.","applies":["crossmember joint","ladder frame"],"basis":"EST: weldment practice (Blodgett, AWS D1.1 detailing); verify the joint by FEA at the load case.","sources":["blodgett-weldments","aws-d1-1"],"tags":["gusset","joint"],"value":{"min":1.5,"unit":"ratio"}},{"id":"ldd-hole-to-weld","kind":"rule","tier":1,"title":"Hole-to-weld distance","summary":"Keep a hole edge >= 2 x plate thickness (and >= 6 mm) from a weld toe: the heat-affected zone, distortion and the weld-toe stress riser should not overlap a hole edge.","applies":["ladder frame","chassis rail","fabricated frame","plate"],"basis":"EST: Blodgett detailing guidance on HAZ and distortion; AWS D1.1 for fatigue categories.","sources":["blodgett-weldments","aws-d1-1"],"tags":["weld","hole","haz"],"value":{"min":6,"unit":"mm"}},{"id":"ldd-verify-after-removal","kind":"rule","tier":1,"title":"Re-verify after every cut","summary":"After lightening, rerun the stress solve at design load: peak von Mises incl. Kt <= yield / 1.5 (EST) and report mass removed. Reject a cut that drops the safety factor under target; stop when mass stops falling.","applies":["all load-driven parts"],"basis":"EST: 1.5 on yield is a common static factor for non-critical structure; the project sets its own target.","sources":["roark","peterson-kt"],"tags":["fea","verify","safety-factor"],"value":{"min":1.5,"unit":"ratio"}}]}