GearForge

Parametric gears and drives, written in Rust: involute gears (including crossed helical pairs), timing belt pulleys, chain sprockets, cycloidal drives, Geneva drives and ratchets. Pick a type or a preset, edit the parameters with a live 3D or top view, watch the parts turn at their real ratios, check how each pair meshes, and export everything in one click: print files, CAD files (including one STEP assembly), A4 drawings, and scripts that rebuild gears parametrically in Inventor or SolidWorks. Add a printable gearbox housing, engrave a label, tune the print files to your printer, or copy an existing gear from caliper readings or a scan.

Types

Type	What you get
Spur / helical gear	One gear, or a compound stack on one axis. Each stage can be spur, helical or herringbone, with face recesses, lightening and edge chamfers. Optional fillet or chamfer where a smaller stage meets a larger one, a raised hub with a set screw, an engraved label, and up to two mating gears placed in mesh, on parallel or crossed shafts.
Internal ring gear	Teeth on the inside of a rim, spur, helical or herringbone
Rack	Straight or helical rack with a solid back
Bevel gear	Straight bevel for any shaft angle, sized from the mating gear's tooth count
Worm and wheel	Worm with 1–8 starts plus its matching wheel, positioned at the right centre distance. The wheel is throated (cut the way the worm would cut it) or a plain helical gear
Planetary set	Sun, planets and ring, phased so they mesh. Spur, helical or herringbone
Timing belt pulley	GT2 (2, 3 and 5 mm) and HTD (3M, 5M and 8M) pulleys with flanges, a hub and set screw. Optionally a driven pulley at the centre distance a closed belt sets, with the belt drawn
Chain sprocket	ISO 606 tooth form for standard roller chains (#25, #35, #40, #50, #60, 05B, 06B, 08B and 1/2 × 1/8 bicycle), with chamfered tooth sides and a hub. Optionally a driven sprocket at the centre distance a chain length sets, with the chain drawn
Cycloidal drive	One or two lobed discs, a housing with printed ring pins or pockets for dowels, the eccentric cam and the output carrier with its pins
Geneva drive	A slotted wheel that turns one slot for each turn of its crank and is locked in between: 3 to 18 slots
Ratchet and pawl	A saw-toothed wheel that turns one way only, with a pawl shaped to sit in its teeth

Every design can use a round, keyway, D-flat, double-D, hex or involute spline bore. Keyways default to DIN 6885 sizes for the bore diameter: for example a 2 mm key on a 6–8 mm shaft, or 5 mm on 12–17 mm.

Spline bores follow DIN 5480 (30° involute, flat root). The module and tooth count come from the standard for the bore diameter, or set your own; Spline fit is the play on each flank. Give a Shaft length and GearForge makes the matching spline shaft as its own part to print.

Stronger teeth

• Root fillet: each tooth root is the curve a rack cutter with rounded tips leaves (the trochoid), set as the cutter tip radius in modules (ISO 53 uses 0.38). Small pinions get their real undercut. Set it to 0 for the old plain radial root.
• Tip rounding: rounds the tooth tip corners by a radius in mm. About 0.1–0.2 mm stops printed tips curling and catching.
• Edge chamfer: a 45° chamfer on the tooth edges of a stage's open top and bottom faces (a face covered by a larger stage is left square). 0.2–0.4 mm stops the first layer squashing out into the teeth and helps gears slide into mesh.

All three are under Tooth form in each stage card.

Recesses, lightening and hubs (spur / helical stacks)

• Face recesses: an annular pocket in the top and/or bottom face of any stage, between an inner and outer diameter, at any depth. This suits copying moulded gears. Fit sizes a recess to all the free room on that face: outside the bore, hub or neighbouring stage, and inside a solid rim under the teeth.
• Recess down to the next stage's teeth: on a face where a smaller stage sits, tick Run in to stage N's teeth. The recess then has no inner edge. The smaller stage's teeth carry on down to the recess floor, twisting on if they're helical. The stage fillet or chamfer moves down to the floor with them. That puts the joint below the face the smaller stage's mating gear runs against, so a big fillet or chamfer can't catch it.
• Stage joint: where a smaller stage meets a larger one, fill the inside corner with a fillet (a quarter circle) or a 45° chamfer, which fills more of the corner and prints without support.
• Lightening: round holes, or spokes with rounded windows, between a solid hub and a solid rim. They can sit inside a recess. Fit sizes them to the free room.
• Hub and set screw: a raised collar on the top or bottom face, with an optional radial set-screw hole along +X, lined up with the keyway or flat. The hole can be round (stepped in 0.15 mm layers) or square (prints without support). Buttons fill in tap-drill sizes for M2 to M5.

GearForge checks that everything fits:

• recesses leave a rim and clear the bore;
• a recess that runs in to the next stage clears its teeth and the joint;
• lightening sits wholly inside or outside each recess;
• edge chamfers stay clear of the rim;
• the hub fits its face.

Throated worm wheels

By default the worm wheel is cut the way its worm would cut it. Each slice through the wheel is made by rolling the worm's thread through mesh at the right ratio, the way a hob cuts a real wheel. The hob is slightly oversize: 0.25 module deeper, for root clearance, and thicker by the backlash.

The result:

• The teeth wrap round the worm, with a concave throat on the tips.
• The worm touches along a line instead of a point, so it carries more load and wears less.
• The wheel is phased to mesh with the worm in the assembly and the animation.

Turn off Throated on the Wheel card for a plain helical wheel. A throated wheel's face width is limited so the worm can still reach its faces; the card shows the limit.

Belt pulleys

Grooves follow each belt's published groove shape. GT2 grooves have a round bottom and larger flank arcs; HTD grooves are one arc. Each groove's corner is rounded onto the outside diameter, which is the pitch diameter less twice the belt's pitch line offset. A 20-tooth GT2 2 mm pulley comes out 12.22 mm across, as bought ones are.

• Groove clearance opens every groove up for printers that close small gaps. Try 0.05 mm steps if the belt won't seat.
• Belt drive: add a driven pulley and give the closed belt's length, in teeth or mm. GearForge works out the centre distance and shows how many belt teeth wrap the small pulley. Under 6 teeth, the belt can jump.
• The belt appears in the 3D and top views and in the STEP assembly, but isn't exported to print.

Chain sprockets

Teeth use the ISO 606 form, taking the middle of the standard's range: a roller seat, then a convex flank up to the tip. Pick a chain size and its pitch, roller diameter, width and plate height fill in; or enter your own under Chain sizes.

• Tooth width is 0.93 or 0.95 of the chain's inside width.
• The tooth sides are rounded towards the tips so the chain finds its way on.
• Seat clearance enlarges the roller seats for printing.
• The hub is kept small enough to clear the chain's plates.
• Chain drive: add a driven sprocket and a chain length in links for the centre distance. The chain is drawn but not exported.

Cycloidal drives

The ring has N pins and the disc N − 1 lobes, so the reduction is (N − 1) : 1, with the output turning the opposite way. The disc's outline is worked out exactly from the pin path: it touches every pin at every input angle, which the tests check.

• Two discs half a turn apart balance the drive. When the lobe count is odd and the output pin count even, they're the same part. Otherwise GearForge makes the second disc with its holes turned to match.
• Pins are printed as part of the housing, or the housing has pockets for steel dowel pins, which run smoother.
• Bearing buttons fill in common bearings (608, 6000, 67xx, 68xx). The eccentric cam carries the bearing's inside, and each disc's centre hole takes its outside.
• Output: pins on a carrier above the housing pass through holes in the discs.
• Checks: the eccentricity stays under the limit where lobes cross, the pins stay smaller than the tightest lobe curve, and the holes, bearing and cam all fit.

The animation shows the discs riding the cam and turning back slowly against the input.

Geneva drive

A crank pin enters a slot in the wheel, turns it one slot (360° ÷ slots), and leaves. In between, the crank's locking disc sits in the wheel's concave arc and holds it still. With 4 slots the wheel moves for 90° of each crank turn and is locked for the other 270°; more slots give smaller steps and a longer dwell. The wheel turns the opposite way to the crank.

• Everything is sized from the slots, the centre distance and the pin: the pin circle, the slots, the locking arcs and the cut in the locking disc that lets the wheel through.
• The crank is a base plate carrying the locking disc and the pin. The wheel sits above the plate, its faces flush with the locking disc.
• Clearance opens the slots round the pin and the locking arcs round the disc.
• The tests step the crank through a full turn and check the wheel never touches it, and that the wheel can't turn while it's locked.

The animation shows the wheel index and stop.

Ratchet and pawl

The wheel turns freely anticlockwise (seen from the top) and locks clockwise. Each tooth rises steeply from its valley, the locking face, and slopes down to the next.

• Hook angle leans the locking faces back from radial: under load a hooked face pulls the pawl in rather than pushing it out. 5–10° is usual.
• Tooth depth 0 picks about half the tooth pitch.
• The pawl pivots above the teeth, clear of them. Its tip runs down the locking face and is shaped to sit in the valley with the clearance all round. Its pivot sits above the line of the locking force, so the load holds it in.
• The pawl's pivot bore and length are settable. Hold it against the wheel with a light spring or a rubber band.

The animation shows the pawl riding up each tooth and dropping into the next valley. The tests check it never cuts into the wheel, and that turning back runs the locking face into its tip.

Crossed helical gears

A mating gear can sit on a shaft that crosses the stack's at an angle, rather than parallel: pick Crossed on the mating-gear card and give the shaft angle (90° for square shafts).

• The two helix angles add up to the shaft angle, so give the stage a helix of about half of it. 45° each, same hand, is the usual square-shaft pair. GearForge works out the mate's helix and hand.
• They share the normal module and pressure angle. The ratio is the tooth ratio, not the diameter ratio.
• The mate is placed at the right distance, square to both shafts, through the middle of the stage's face width, and turned so its teeth fall between the stage's. The tests turn the pair and check no tooth of one enters the other.
• They touch at a point and slide along the teeth, so they suit light loads, need grease and wear in. The mesh analysis and strength guide cover parallel shafts only, and the top view can't show a crossed mate (the 3D view does).

Engraved labels

Text cut into a stage face, set round the bore so it reads from outside: the teeth and pitch ("27T 32DP") unless you type your own. Pick the stage, the face, the depth (0.4–0.6 mm reads well) and the height, or leave the height at 0 to fill the room.

• The letters are a single-stroke font stroked to a printable width, about 0.15 of their height and at least 0.4 mm. Capitals, digits and - + = / . : × ° Ø are covered.
• A label on a bottom face is mirrored so it reads the right way round with the gear turned over.
• It keeps clear of the bore, hub, neighbouring stage, recesses, lightening and the rim under the teeth, and says if it won't fit.
• It's in every output: the print files, both STEP files and the CAD scripts.

Gearbox housing

For spur and helical stacks with their mating gears, belt drives and chain drives: two plates on pillars that hold every shaft at its centre distance.

• Bearings picks a bearing for each shaft from 683 to 6804 and gives both plates a pocket for it, with Bearing fit for a press fit. Without them, plain shaft holes with clearance.
• Pillars are spaced round the outline with tap holes in the bottom plate and clearance holes in the top one, for M2 to M4 screws.
• Gaps between the parts and the plates, and round the largest gear on each shaft.
• The shafts and bearings appear in the views for reference. The plates have their own drawings.

Print fit

Corrections for how your printer prints, applied to the print files only (STL, 3MF and OBJ). STEP, drawings and the CAD scripts stay at the true sizes.

• Hole compensation is added to every hole's diameter: bores, bearing pockets, pin holes. Printed holes usually come out 0.1–0.2 mm small.
• First-layer inset pulls the bottom layer's edges in, and its holes out, so the squashed first layer ends up the right size. It's left off any part where doing so would run two edges together.

Copy from a scan

Lay the gear on a flatbed scanner, or photograph it square-on beside a ruler, and open the image in Copy from a scan.

• Scale: the scanner's DPI, or click two marks on the ruler a known distance apart.
• GearForge separates the gear from the background, finds its centre and traces the outline all round. Click near the centre first if more than one thing is in the picture.
• It counts the teeth (or give the count), measures the tip and root, and fits real involute outlines to the trace: each candidate module or DP, pressure angle and profile shift is listed with how far it is from the trace.
• The traced edge (green) and the chosen gear (orange) are drawn over the picture. One click copies the gear into the design.

Drawings

An A4 drawing for every part, as PDF and SVG:

• a front view with tip, pitch and root circles;
• a side view with the diameters and thicknesses;
• a gear data table (teeth, module, pressure angle, helix, profile shift, diameters, tooth thickness and root form) and the part's features;
• a title block. The scale is picked from the usual ratios to fit the sheet.

Pulleys, sprockets, cycloidal discs, Geneva and ratchet parts and the housing plates get the same sheet with their own data.

Mesh analysis

For every meshing pair in a design, GearForge reports:

• Pairs covered: a stage with its mating gears, sun with planet, planet in ring, worm with wheel, and a bevel gear with its mate.
• Contact ratio: how many tooth pairs share the load on average, plus helical overlap. Under 1 the gears knock; 1.2 or more runs smoothly. Only the true involute counts, so a pinion whose root is undercut gets the lower figure it really runs at.
• Backlash: the real play between the teeth at the centre distance the parts are built at. Mates of a shifted gear sit slightly further out, which opens the backlash a little.
• Root clearance: the smallest gap between one gear's tips and the other's roots.
• Rolling check: the real tooth outlines, root fillets and all, are rolled through a full tooth pitch. Any overlap means the teeth will jam or grind. This finds tip interference the formulas can't judge. For example, a standard 18-tooth planet in a 48-tooth ring overlaps by 0.02 mm with no backlash, and runs clear with 0.1 mm.
• Stepped through mesh: at 36 steps through a tooth, GearForge finds how far the driven gear can turn either way before the teeth touch. That gives the play at every step, and where the driven gear sits against the tooth ratio when driven forward and back (transmission error). The inspector draws it over three teeth; flat lines run smoothly, steps mean the teeth hand over with a jolt, red is where they jam. Good involute pairs stay within a micron or two (the outlines' facets). The real outlines can show what the involute sums don't: in that 18-tooth planet in its 48-tooth ring, the play is the full 0.2 mm as the teeth pass the pitch point, but closes to 0.155 mm between as the ring's tips come near the planet's flanks.

Each pair is rated runs smoothly, runs roughly or won't run properly, with what to change. The analysis is in the inspector's Mesh card and the spec sheet, and problems show under Warnings.

Measure a gear

Copying an existing gear needs a few caliper readings:

• Teeth and outside diameter: enough to find the nearest module or DP, assuming 20° and no profile shift.
• Span over k teeth: close the jaws over k teeth so they rest on the flanks. This gives the profile shift.
• Span over k + 1 teeth as well: the two spans differ by exactly one base pitch, π × m × cos α, whatever the shift. That tells the module and pressure angle apart (14.5°, 15°, 20°, 22.5°, 25°).
• Root diameter and helix angle: optional, for a further check and for helical gears.

The tool lists the best candidates with how closely each predicts every reading, and copies the teeth, module, pressure angle and shift into a stage with one click. Caliper readings to 0.01 mm are enough: the tests recover a 27-tooth 32 DP gear from rounded, slightly-off readings.

The editor

• Header: menu, new and preset, open, save, undo and redo, the inspector toggle, and Export.
• Left panel: the type, then a card per stage (with Tooth form and Recesses & lightening folds), the hub, two mating-gear cards (position each around the stack in degrees, on parallel or crossed shafts), the housing, the bore shape, the label, print fit and the resolution. Hover any field for an explanation. Module and diametral pitch are linked.
• Middle: the view.
  • 3D: GPU-rendered, with a floor grid and axes. Drag to orbit, right-drag or Shift-drag to pan, scroll to zoom, double-click to re-centre. Iso, Top, Front and Right buttons; perspective or orthographic.
  • Top: the profiles with tip, pitch and root circles, a mm grid and a scale bar.
  • Play: turns every part at its true ratio (Space to play or pause). Geneva wheels index and stop, and pawls ride the ratchet's teeth.
  • The camera button saves a PNG of the view.
• Right panel (inspector):
  • Summary: mass in the chosen material, volume, pieces to print and the overall size.
  • Parts: each part's mass. Belts, chains and dowel pins are listed as shown only.
  • Mesh: the mesh analysis for every pair, with a verdict, its play through mesh and a small plot of the driven gear against the tooth ratio.
  • Strength: the largest tooth load and torque each gear should carry before its teeth bend, at the speed you enter. It uses the Lewis equation with the Barth speed factor and the material's allowed stress, as a rough guide: no wear, heat or shock. It covers involute gears; belts and chains have ratings from their makers.
  • Warnings, and the full spec sheet with a Copy button.
• Tools:
  • Measure a gear: works out the module or DP, pressure angle and profile shift of a gear you've measured, and copies them into the design.
  • Copy from a scan: the same from a scan or photo of the gear.
  • Gear train: give it a reduction and it finds tooth counts for one pair, or for an input pinion → compound gear → output gear. Use builds the train as a stack with both mates. A hub that no longer fits the new stages is shrunk to fit, or turned off if it can't.
  • Clearance test: a test print with numbered gear pairs at several backlash values on a pin plate. Print it, try each pair, and use the tightest that turns freely. It exports STL, 3MF and a legend.

Run it

Download: get gearforge.exe from the latest release. It's a single program for 64-bit Windows 10 or 11, with nothing to install. The first time you run it, Windows may say it protected your PC because the program isn't signed: choose More info, then Run anyway.

Double-click gearforge.exe, or from a terminal:

gearforge                            # open the editor
gearforge my_gear.toml               # open the editor with a gear file
gearforge export my_gear.toml out    # write every format without opening the editor
gearforge example > my_gear.toml     # start a new gear file

Files and folders

• Gear files: New, Open, Open recent, Save and Save as, using normal Windows dialogs. The title bar shows * when there are unsaved changes, and you're asked before anything is lost. Ctrl+N new, Ctrl+O open, Ctrl+S save, Ctrl+Shift+S save as, Ctrl+E export.
• Export: pick the folder, tick the formats, and optionally open the folder afterwards.
• Remembered between runs: your current gear (even if unsaved), the gear file, recent files, export folder, format choices, view, camera, theme, window size, the strength speed and the clearance-test settings. These live in %APPDATA%\GearForge\data\app.ron.
• Defaults: gear files and exports go to Documents\GearForge until you choose elsewhere.

Outputs

File	Use
.stl	3D printing (binary, watertight, mm). One per part; _x3 in the name means print three.
.3mf	3D printing: every part (and every copy) as its own object, laid out side by side on the bed
_assembly.stl / .obj	Every part in its working position, for checking fit
_assembly.step	A STEP assembly: each part defined once and every copy placed where it works, so CAD opens it as an assembly of named components (planet:1, planet:2 …). Parts use smooth geometry where they have it, faceted otherwise (bevel gears, belts and chains)
.obj	Mesh for Blender and similar tools
.step	CAD import. Faceted solid: flat facets, includes every feature
_smooth.step	CAD import with true geometry. Straight walls are flat faces, real cylinders and extruded B-spline flanks, merged across features. Helical and herringbone teeth, worms and throated wheels are smooth B-spline surfaces. Every type except bevel gears. It leaves out the stepped stage fillet or chamfer, edge chamfers, the set-screw hole and sprocket tooth chamfers (add them in CAD), and the spec sheet says so
_<profile>.dxf	2D profile (with lightening) for laser, waterjet or CNC: gear stages, pulleys and flanges, sprockets, cycloidal discs and housing, Geneva and ratchet parts
_drawing.pdf / _drawing.svg	An A4 drawing per part: views, dimensions, gear data and title block
_<profile>.svg, _all_profiles.svg	2D profiles at true scale in mm
.scad	OpenSCAD: profiles as polygon modules, parts as polyhedron, plus the assembly
_spec.txt	Dimensions, span measurement, root form, recesses, lightening, hub, label, ratios, centre distances, belt and chain lengths, Geneva and ratchet motion, housing, print fit, mesh analysis, volume and weight
.toml	The gear file, to reload or batch-export later
_inventor.iLogicVb	Inventor iLogic rule that builds the gear with editable parameters

The smooth STEP files were checked by importing them into Inventor 2026, covering:

• spur, helical, herringbone, rack, ring and planetary parts;
• worms and throated wheels;
• GT2 and HTD pulleys, sprockets, and cycloidal discs, housings, cams and output carriers;
• Geneva cranks and wheels, ratchet wheels and pawls, and a gear with an engraved label.

Each comes in as a single valid solid. Volumes are within 0.1% of GearForge's own, and the worm within 0.5%, the gap being GearForge's mesh.

STEP assemblies of a planetary set, a worm drive, a cycloidal drive, a belt drive, a Geneva drive, a ratchet and a crossed helical pair open in Inventor 2026 as assemblies. Every component comes in at the right position and angle (the crossed mate with its axis square to the stack's), with the right volume.

Parametric gears in Inventor and SolidWorks

GearForge writes a script that builds the gear natively in your CAD package, with real involute curves (splines and arcs, not facets) driven by named parameters. The scripts cover the involute gear types; take pulleys, sprockets and cycloidal drives into CAD with smooth STEP.

Inventor (*_inventor.iLogicVb):

1. Start a new part from a metric (mm) template.
2. Manage tab > iLogic > Add Rule, paste the file's contents, then Save & Run. You can also run the file directly as an external rule.
3. The setup creates user parameters (Manage > Parameters) and a rule named GearForge.
   • Per gear or stage: Teeth1, Module1, Thickness1, PressureAngle1, Shift1, Backlash1, Addendum1, Dedendum1, HelixAngle1, Hand1 (1 right, -1 left), Herringbone1 (0 or 1), RootFillet1 (cutter tip radius / module), TipRound1 (mm), EdgeChamfer1 (mm).
   • Recesses, when a stage has them: RecessBottom1 (1 on, 0 off), RecessBottomID1, RecessBottomOD1, RecessBottomDepth1, RecessBottomToStage1 (1 = run in to the next stage's teeth), and the same for RecessTop….
   • Lightening: Lighten1 (0 none, 1 holes, 2 spokes), LightenCount1, LightenID1, LightenOD1, LightenWeb1, LightenCorner1.
   • The hub: HubOn, HubOnTop, HubDia, HubLength, SetScrew, ScrewDia, ScrewRound.
   • A label: LabelDepth. The text and its layout are fixed when GearForge exports; the rule draws them as sketch outlines and cuts them to depth.
   • For the whole part: BoreDia, BoreShape, KeyWidth, KeyDepth, FlatDepth, FilletRadius, JointChamfer (1 = chamfer the stage joints, 0 = fillet), plus RimDia for rings and BackHeight for racks.
   • Bevel gears add MateTeeth, ShaftAngle and BackThickness. Worms use WormModule, Starts, PitchDia, WormLength, PressureAngle, Backlash, Addendum, Dedendum and Hand.
4. Change any parameter and the GearForge rule rebuilds the gear. Modules can be written as 25.4 mm / 32 to work in diametral pitch.

Every involute gear type is supported:

• spur, helical and herringbone stacks with bore, stage fillets or chamfers, root fillets, tip rounding, edge chamfers, recesses (including ones that run in to the next stage's teeth), lightening, hub and set screw;
• internal rings and racks;
• straight bevel gears, as a loft to the cone apex;
• worms, with each thread a coil feature;
• throated worm wheels, lofted through sections cut by the worm (the same calculation as GearForge's), or plain helical wheels;
• the planetary sun, planet and ring (one rule each);
• mating gears, including crossed helical mates (each is its own helical gear).

Geneva drives and ratchets go to CAD as smooth STEP.

All of them were run in Inventor 2026. Each solid's volume matches GearForge's own to within about 0.5%, and for every feature design 600 sample points agree on inside and outside with GearForge's model. That covers the thread hand and phase, the side the set screw is on, and where the spokes sit.

Inventor can't fillet a stage joint tighter than the curved tooth roots. When that happens, the rule steps the fillet radius down until it fits and says so on the status bar. Edge chamfers that would run into each other on narrow tooth tips step down the same way.

Inventor can't fillet or chamfer the edges of helical (lofted) teeth. The rule leaves those features off and says so; the print files have them.

Labels were checked in Inventor 2026 on a bottom face and a top face: deepening the label from 0.4 to 0.8 mm removes 5.64 and 12.51 mm³, against 5.6 and 12.5 mm³ in GearForge's own models.

The recess and chamfer features were checked in Inventor 2026 against 600 sample points each:

• A bottom-face recess that runs in to the next stage, with a fillet: every point agrees.
• A top-face one with a joint chamfer and edge chamfers on all three open faces: 599 agree. The last sits within 0.04 mm of a face, where GearForge's thin chamfer layers differ from the true chamfer by 15 µm. The rule recreates the features, sketches and work planes named GF_… on each rebuild, so put your own features after them.

SolidWorks (*_solidworks.swb): Tools > Macro > Run and pick the file. It adds global variables with the same names (Tools > Equations). Edit them and run the macro again to rebuild. It builds the same features:

• helical and herringbone stages as lofts;
• bevel gears as a loft;
• worms as a helix with a swept thread.

It also builds throated worm wheels as a loft. Helical ring teeth are built straight. The macro hasn't been run in SolidWorks yet. Its structure is checked automatically, but treat it as a first draft and report anything it gets wrong.

The 27T / 17T example

The example is a 27-tooth gear 23 mm across and 2.5 mm thick, under a 17-tooth gear 4 mm thick, with a 0.4 mm fillet where they meet. 23 mm over 27 teeth fits 32 diametral pitch (module 0.79375, OD 23.02 mm) better than module 0.8 (OD 23.2 mm). Use Measure a gear in the app with spans over 3 and 4 teeth to confirm the pitch, pressure angle and any profile shift.

To copy a gear with recessed faces:

1. Tick Bottom face recess on the 27T and Top face recess on the 17T.
2. Press Fit.
3. Set the measured diameters and depths.

How the geometry is approximated

• Root fillet: the trochoid is traced by rolling the cutter's tip circle around the gear, then sampled. The involute flanks are sampled at the flank-points setting.
• Stage fillet or chamfer: built from 8 thin layers that follow the tooth outline. Each layer is under 0.1 mm, so slicers see a smooth fillet. A mating gear can't use the bottom fillet-height strip of that face, unless the joint sits in a recess that runs in to the teeth. On a helical stage the helix starts above the fillet.
• Edge chamfers: 3 to 12 layers about 0.05 mm thick, each pulled in from the tooth outline, so slicers see a smooth bevel.
• Round set-screw holes: stepped in thin layers in the print files. The CAD scripts cut a true cylinder.
• Bevel gears: Tredgold's back-cone tooth on a flat back face, ruled straight to the cone apex, ending on a flat front face, with material behind the teeth.
• Worm wheel: the throated wheel is cut by rolling the worm's thread through mesh in thin slices. The slices are joined face to face, and in CAD lofted through sections.
• Sprocket tooth sides: ISO 606 rounds them with a radius of one pitch. GearForge takes 0.1 pitch off each side at the tip, through 4 thin ruled layers per face.
• Belts and chains are drawn as plain bands (and rollers) for reference only.
• Labels: each letter's centre-lines are stroked to width with round ends and joins, and the strokes of the whole label are merged into one set of outlines (with islands inside letters such as O) before they're cut.
• Geneva and ratchet outlines are built from circles and polygons with exact boolean operations. The pawl's motion is found by stepping the wheel through a tooth and swinging the pawl until it just clears.
• Stepped through mesh: each step looks only at the teeth near the pitch point, where the two gears' tooth rings overlap. A test checks it against turning the whole outlines.
• Strength: Lewis bending only (form factors for 20° full-depth teeth, adjusted for other pressure angles, virtual tooth counts for helical and bevel gears) and the Barth speed factor.

Building

Needs Rust (rustup, GNU toolchain) and MinGW-w64 on PATH (WinLibs from winget works). Build from a short folder path: a very deep path breaks some Windows build scripts. Crates used beyond eframe include image (scans) and i_overlay (polygon booleans for labels and mechanisms).

cargo test --release
cargo build --release

Source:

• gear.rs: parameters, involute and trochoid maths, design checks
• drives.rs: belt pulley grooves, ISO 606 sprocket teeth, cycloidal discs, belt and chain lengths
• mechanisms.rs: Geneva drives, ratchets and pawls, and their stepped motion
• label.rs: the stroke font and label layout
• housing.rs: gearbox housing layout, bearings and screws
• scan.rs: tracing a gear from an image and fitting involutes to it
• drawing.rs: A4 drawings as PDF and SVG
• analysis.rs: mesh analysis (contact ratio, backlash, clearance, rolling check, stepping through mesh)
• matching.rs: measure and match (module, pressure angle and shift from caliper readings)
• geom.rs: 2D helpers, offsetting and rounding
• layers.rs: the layered-solid builder (bands of loops, worked-out steps between them)
• model.rs: stacks with fillets, recesses, lightening and hubs; rings, racks, bevels, worms, planetary sets, pulleys, sprockets and cycloidal drives; meshing and assemblies
• brep.rs: smooth STEP (lines, arcs and B-spline fitting, advanced B-rep) and STEP assemblies
• earcut.rs: face triangulation
• export.rs: file writers (STL, 3MF, OBJ, STEP, DXF, SVG, OpenSCAD) and spec sheets
• strength.rs, train.rs, testprint.rs: strength estimate, gear train search, clearance test
• cad.rs, solidworks.rs: Inventor iLogic rule and SolidWorks macro generators
• gui/: the editor
• docs/: the project website (GitHub Pages) and its images

Contact

Questions, ideas or something that doesn't work? Email [email protected], or open an issue on GitHub.

Licence

GearForge is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License, version 3, as published by the Free Software Foundation. It is distributed in the hope that it will be useful, but without any warranty; see LICENSE for details.