{"$schema":"nativecad-dfm-pack/1","id":"robotics","title":"Robotics -- shafts, bearings, gears, belts, motors and linkages","sector":"robotics","version":"2026-09-03","summary":"Shaft and bearing standards, gear and GT2/HTD belt geometry, lead-screw and coupling sizes, NEMA/servo/BLDC motor mount patterns, linkage fits, 3D-printed structural rules, and the tests a robot's moving parts are held to.","aliases":["robot","robot arm","actuator","shaft","bearing","gear","pulley","gt2","stepper","nema 17","nema 23","servo","lead screw","coupling","linkage","gripper","motion"],"crossSector":false,"size":"core","sources":[{"id":"din-6885","title":"DIN 6885-1:1968 Drive type fastenings without taper action -- Parallel keys, keyways","url":"https://www.din.de/en","accessed":"2026-09-03"},{"id":"iso-286","title":"ISO 286-2:2010 Geometrical product specifications (GPS) -- ISO code system for tolerances on linear sizes -- Part 2: Tables of tolerance classes","url":"https://www.iso.org/standard/45469.html","accessed":"2026-09-03"},{"id":"skf-bearing-catalogue","title":"SKF Rolling Bearings Catalogue (dimension tables, shoulder diameters, fit recommendations)","url":"https://www.skf.com/group/products/rolling-bearings","accessed":"2026-09-03"},{"id":"gates-gt2-design-manual","title":"Gates PowerGrip GT2 Belt Drive Design Manual","url":"https://www.gates.com/content/dam/gates/master-portfolio/master-brand-en/pdfs/powergrip-gt2-design-manual.pdf","accessed":"2026-09-03"},{"id":"khk-gear-tech-ref","title":"KHK Stock Gears -- Gear Technical Reference (module, pressure angle, backlash, undercut)","url":"https://khkgears.net/new/gear_knowledge.html","accessed":"2026-09-03"},{"id":"nema-ics-16","title":"NEMA ICS 16-2001 (R2016) Motion/Position Control Motors, Controls and Feedback Devices","url":"https://www.nema.org/standards/view/motion-position-control-motors-controls-and-feedback-devices","accessed":"2026-09-03"},{"id":"stepperonline-nema-mech","title":"StepperOnline NEMA 14/17/23/34 hybrid stepper motor mechanical drawings (frame, bolt pattern, pilot, shaft)","url":"https://www.omc-stepperonline.com/","accessed":"2026-09-03"},{"id":"iso-724-trapezoidal","title":"ISO 724:1993 ISO general purpose metric trapezoidal screw threads -- Basic dimensions","url":"https://www.iso.org/standard/4759.html","accessed":"2026-09-03"},{"id":"matweb-materials","title":"MatWeb Material Property Data (shafting steels, engineering plastics)","url":"https://www.matweb.com/","accessed":"2026-09-03"}],"entries":[{"id":"shaft-standard-diameters","kind":"dimension","tier":1,"title":"Standard robotics shaft diameters (h6/h7)","summary":"Common robot shaft/axle diameters are 3, 4, 5, 6, 8, 10, 12, 15 and 20 mm, turned to h6 (precision bearing/pulley register) or h7 (looser register, e.g. printed hubs) per ISO 286.","applies":["shaft","axle","gear shaft","pulley shaft"],"value":{"options":[3,4,5,6,8,10,12,15,20],"unit":"mm"},"basis":"ISO 286 shaft tolerance classes: h6 for a bearing-seat register, h7 where the mating bore is coarser (3D-printed hub, clamp coupling)","sources":["iso-286"],"tags":["shaft","tolerance","h6","h7"]},{"id":"shaft-keyway-din6885","kind":"fastener","tier":1,"title":"Parallel keyway width/height/depth by shaft diameter (DIN 6885)","summary":"DIN 6885-1 parallel keys by shaft dia: 6->2x2 (t1 1.2), 8->2x2 (t1 1.2), 10->3x3 (t1 1.8), 12->4x4 (t1 2.5), 15->5x5 (t1 3.0), 20->6x6 (t1 3.5) mm -- b x h key cross-section, t1 the shaft-side depth.","applies":["shaft","keyway","key","coupling","pulley"],"value":{"table":[{"shaftDia":6,"b":2,"h":2,"t1":1.2},{"shaftDia":8,"b":2,"h":2,"t1":1.2},{"shaftDia":10,"b":3,"h":3,"t1":1.8},{"shaftDia":12,"b":4,"h":4,"t1":2.5},{"shaftDia":15,"b":5,"h":5,"t1":3},{"shaftDia":20,"b":6,"h":6,"t1":3.5}],"unit":"mm"},"basis":"DIN 6885-1 form B square-ended parallel key table, keyed by shaft diameter range","sources":["din-6885"],"tags":["shaft","keyway","din-6885","key"]},{"id":"shaft-dflat-setscrew-depth","kind":"feature","tier":1,"title":"D-flat depth for set-screw shaft retention","summary":"A milled D-flat for a set screw (common on 5 mm NEMA 17 and small gearmotor shafts) is cut 0.5-1.0 mm deep, centred on the shaft so the set screw seats flat rather than point-loading round stock.","applies":["shaft","stepper shaft","set screw","coupling"],"value":{"min":0.5,"max":1,"typical":0.7,"unit":"mm"},"basis":"Common hobby-drivetrain practice for stepper and gearmotor output shafts (StepperOnline mechanical drawings show a flat on the 5mm/6.35mm shaft)","sources":["stepperonline-nema-mech"],"tags":["shaft","d-flat","set-screw"]},{"id":"bearing-common-sizes-table","kind":"dimension","tier":1,"title":"Common robotics deep-groove ball bearing sizes (bore x OD x width)","summary":"Bearings used across robot joints: 608 8x22x7, 6000 10x26x8, 6001 12x28x8, 6002 15x32x9, 6004 20x42x12, 623 3x10x4, 625 5x16x5, 626 6x19x6, 688 8x16x5, MR105 5x10x4 (all mm).","applies":["bearing","joint","pulley bearing"],"value":{"table":[{"designation":"608","bore":8,"od":22,"width":7},{"designation":"6000","bore":10,"od":26,"width":8},{"designation":"6001","bore":12,"od":28,"width":8},{"designation":"6002","bore":15,"od":32,"width":9},{"designation":"6004","bore":20,"od":42,"width":12},{"designation":"623","bore":3,"od":10,"width":4},{"designation":"625","bore":5,"od":16,"width":5},{"designation":"626","bore":6,"od":19,"width":6},{"designation":"688","bore":8,"od":16,"width":5},{"designation":"MR105","bore":5,"od":10,"width":4}],"unit":"mm"},"basis":"SKF Rolling Bearings Catalogue dimension tables for the 60x/62x/68x deep-groove series and MR miniature series","sources":["skf-bearing-catalogue"],"tags":["bearing","608","6000","6001","6002","6004","dimension"]},{"id":"bearing-housing-shaft-fits","kind":"tolerance","tier":1,"title":"Bearing housing bore and shaft fit classes","summary":"House the outer ring in an H7 bore. Fit the shaft: k6 where the inner ring rotates with the shaft (a light interference press, the normal robot-joint case), h6 where the shaft is stationary and the outer ring/housing rotates (a sliding fit).","applies":["bearing","housing","shaft"],"value":{"options":["H7 housing / k6 shaft (rotating inner ring)","H7 housing / h6 shaft (rotating outer ring)"]},"basis":"SKF fit-selection guidance (rotating-inner-ring load case) applied to ISO 286 shaft/hole tolerance classes","sources":["skf-bearing-catalogue","iso-286"],"tags":["bearing","fit","h7","k6","h6"]},{"id":"gear-module-pressure-angle","kind":"dimension","tier":1,"title":"Gear module and pressure angle for small robot gearing","summary":"Robot gearing is cut to module 0.5, 1, 1.5 or 2 mm at a 20deg pressure angle -- the standard KHK/AGMA rack, so off-the-shelf gears and hobs interchange across vendors.","applies":["gear","gear train","gearbox"],"value":{"options":[0.5,1,1.5,2],"unit":"mm"},"basis":"KHK gear technical reference: standard module series and the 20deg full-depth involute rack","sources":["khk-gear-tech-ref"],"tags":["gear","module","pressure-angle"]},{"id":"gear-min-teeth-undercut","kind":"rule","tier":1,"title":"Minimum tooth count before undercut (20deg pressure angle)","summary":"A 20deg pressure-angle involute gear needs >= 17 teeth to avoid root undercut from rack generation; a pinion below 17 teeth loses root strength unless profile-shifted.","applies":["gear","pinion"],"value":{"min":17,"unit":"count"},"basis":"KHK gear technical reference: undercut limit z_min = 2/sin^2(pressure angle) ~= 17.1 for 20deg","sources":["khk-gear-tech-ref"],"tags":["gear","undercut","min-teeth"]},{"id":"gear-center-distance-formula","kind":"rule","tier":1,"title":"Spur gear centre distance","summary":"Two spur gears of the same module mesh at centre distance a = m(z1+z2)/2 -- module times the summed tooth counts, halved; get the module or a tooth count wrong and the mesh either binds or runs with excess backlash.","applies":["gear","gear train"],"value":{"value":"a = m*(z1+z2)/2","unit":"mm"},"basis":"Standard involute spur-gear meshing geometry (KHK gear technical reference)","sources":["khk-gear-tech-ref"],"tags":["gear","center-distance","formula"]},{"id":"gt2-pulley-pitch-diameter","kind":"dimension","tier":1,"title":"GT2 pulley pitch diameter from tooth count","summary":"A GT2 (2 mm pitch) pulley's pitch diameter is PD = z*2/pi mm -- a 20-tooth pulley pitches at 12.73 mm, a 16-tooth at 10.19 mm; the belt centreline sits on this circle, not the pulley OD.","applies":["gt2","pulley","timing belt"],"value":{"value":"PD = z*2/pi","unit":"mm"},"basis":"Gates PowerGrip GT2 design manual: pitch diameter = teeth x pitch / pi","sources":["gates-gt2-design-manual"],"tags":["gt2","pulley","pitch-diameter"]},{"id":"gt2-belt-widths","kind":"dimension","tier":1,"title":"GT2 belt widths","summary":"GT2 timing belt comes 6 mm or 9 mm wide for light robotics use; match the pulley's flange width to the belt or it walks off the pulley under any side load.","applies":["gt2","belt","timing belt"],"value":{"options":[6,9],"unit":"mm"},"basis":"Gates PowerGrip GT2 design manual standard belt width series","sources":["gates-gt2-design-manual"],"tags":["gt2","belt","width"]},{"id":"nema17-mount-pattern","kind":"dimension","tier":1,"title":"NEMA 17 stepper mounting pattern","summary":"NEMA 17 motors present a 42.3 mm square face, four M3 holes on a 31 mm bolt square, a dia22 mm central pilot boss, and (usually) a dia5 mm output shaft.","applies":["nema 17","stepper","motor mount"],"value":{"table":[{"field":"faceSquare","value":42.3},{"field":"boltSquare","value":31},{"field":"boltSize","value":"M3"},{"field":"pilotDia","value":22},{"field":"shaftDia","value":5}],"unit":"mm"},"basis":"NEMA ICS 16 frame-size convention as realised in NEMA 17 stepper mechanical drawings (StepperOnline)","sources":["nema-ics-16","stepperonline-nema-mech"],"tags":["nema17","stepper","mount","bolt-pattern"]},{"id":"nema23-mount-pattern","kind":"dimension","tier":1,"title":"NEMA 23 stepper mounting pattern","summary":"NEMA 23 motors present a 56.4 mm square face, four bolts on a 47.14 mm square, a dia38.1 mm central pilot boss, and a dia6.35 mm (1/4 in) output shaft.","applies":["nema 23","stepper","motor mount"],"value":{"table":[{"field":"faceSquare","value":56.4},{"field":"boltSquare","value":47.14},{"field":"pilotDia","value":38.1},{"field":"shaftDia","value":6.35}],"unit":"mm"},"basis":"NEMA ICS 16 frame-size convention as realised in NEMA 23 stepper mechanical drawings (StepperOnline)","sources":["nema-ics-16","stepperonline-nema-mech"],"tags":["nema23","stepper","mount","bolt-pattern"]},{"id":"leadscrew-tr8-lead-pitch","kind":"dimension","tier":1,"title":"Tr8 trapezoidal lead-screw pitch and lead options","summary":"An 8 mm trapezoidal lead screw is cut Tr8x2 (single-start, 2 mm lead = 2 mm pitch, self-locking) or Tr8x8 (4-start, 8 mm lead, 2 mm pitch, fast but not self-locking) -- same thread form, very different travel per revolution.","applies":["lead screw","tr8","linear stage"],"value":{"table":[{"designation":"Tr8x2","pitch":2,"lead":2,"starts":1},{"designation":"Tr8x8","pitch":2,"lead":8,"starts":4}],"unit":"mm"},"basis":"ISO 724 metric trapezoidal thread basic dimensions, applied to the Tr8 hobby lead-screw sizes sold with these two lead options","sources":["iso-724-trapezoidal"],"tags":["lead-screw","tr8","pitch","lead"]},{"id":"coupling-bore-sizes","kind":"dimension","tier":1,"title":"Flexible shaft coupling bore combinations","summary":"Motor-to-leadscrew couplings for hobby robotics are stocked as 5x8 mm and 6.35x8 mm bore pairs (NEMA 17's 5 mm or a 1/4 in shaft into an 8 mm lead screw), body OD 19-25 mm.","applies":["coupling","lead screw","nema 17"],"value":{"options":["5x8","6.35x8"],"unit":"mm"},"basis":"Common jaw/beam coupling catalogue bore pairings for stepper-to-leadscrew drivetrains","sources":["stepperonline-nema-mech"],"tags":["coupling","bore","nema17","leadscrew"]},{"id":"tolerance-bearing-bore-position","kind":"tolerance","tier":1,"title":"Position tolerance for a machined bearing bore","summary":"Hold a CNC-machined bearing bore or shaft register to +-0.05 mm position; the same feature on an FDM print only holds +-0.2 mm, so a press-fit bearing pocket sized for CNC will rattle or crack a printed part.","applies":["bearing","bore","tolerance"],"value":{"options":[{"process":"CNC","tolerance":0.05},{"process":"FDM","tolerance":0.2}],"unit":"mm"},"basis":"ISO 286-class positional capability difference between 3-axis CNC and FDM printing","sources":["iso-286"],"tags":["tolerance","bearing","position","cnc","fdm"]},{"id":"shaft-material-steel","kind":"material","tier":1,"title":"Shaft steels: 1045 and 4140","summary":"Turned robot shafts and axles use 1045 (cold-drawn, good machinability, adequate wear resistance unshielded) or 4140 (alloy steel, through-hardenable, used for higher-load or ground shafts); both take a keyway and press-fit bearings without distortion.","applies":["shaft","axle"],"value":{"table":[{"material":"1045 (normalized)","yield_MPa":375,"hardness_HB":170},{"material":"4140 (Q&T)","yield_MPa":655,"hardness_HB":197}]},"basis":"MatWeb property data for AISI 1045 and 4140 bar stock, the two steels most robot shafting is cut from","sources":["matweb-materials"],"tags":["material","steel","1045","4140","shaft"]},{"id":"gear-material-pom","kind":"material","tier":1,"title":"POM (acetal) for machined and printed gears","summary":"POM (Delrin/acetal) is the default plastic gear material: low friction against itself and steel, dimensionally stable, and machines or injection-molds to a clean tooth profile -- density 1.41 g/cm3, tensile ~65 MPa.","applies":["gear","pulley"],"value":{"table":[{"property":"density","value":1.41,"unit":"g/cm3"},{"property":"tensile strength","value":65,"unit":"MPa"}]},"basis":"MatWeb POM copolymer property data, the standard plastic gear/bushing material","sources":["matweb-materials"],"tags":["material","pom","acetal","gear"]},{"id":"print-material-pa12-cfpa","kind":"material","tier":1,"title":"3D-printed structural robot parts: PA12 and CF-PA","summary":"Load-bearing printed brackets, arms and gear housings favour PA12 (SLS nylon, tough, low warp) or carbon-fibre-reinforced PA (CF-PA, higher stiffness, lower creep) over PLA/PETG when the part carries a running joint load.","applies":["3d printed part","bracket","arm","gear housing"],"value":{"table":[{"material":"PA12 (SLS)","tensile_MPa":48,"flex_modulus_MPa":1500},{"material":"CF-PA","tensile_MPa":90,"flex_modulus_MPa":6000}]},"basis":"MatWeb PA12 (SLS) and CF-filled PA property data versus unfilled FDM plastics for load-bearing service","sources":["matweb-materials"],"tags":["material","pa12","cf-pa","3d-print"]}]}