Free gear generator — involute gears to STL, DXF & SVG
Generate true involute spur, helical, herringbone, internal and rack gears. Set module, teeth and pressure angle, watch the pair mesh live, then download a watertight STL for 3D printing or a true-scale SVG / DXF for the laser — free, no signup, nothing uploaded.
Gear
Bore & holes
Fit & precision
For printed gears, 0.1–0.2 mm backlash usually gives a smooth mesh without slop.
Mating gear
Gear tips
- Two gears mesh only with the same module and pressure angle. Mount them at the centre distance shown in the readout.
- Module ≥ 1 mm prints reliably with a 0.4 mm nozzle; add 0.1–0.2 mm backlash so printed pairs don’t bind.
- Herringbone runs quieter than spur and, unlike helical, produces no axial thrust — the favourite for printed gearboxes.
- Under 17 teeth at 20° the root undercuts; add profile shift (+0.3…+0.5) to keep teeth strong.
- Print flat, 100% infill or 4+ walls, and the layer lines will run across the teeth for strength.
Capabilities
What the gear generator does
- True involute tooth profiles — module, pressure angle (14.5° / 20° / 25°), profile shift and backlash, with a trochoid-approximated root fillet.
- Five gear types: spur, helical, herringbone (chevron), internal ring and rack — helical pairs get opposite hands automatically.
- Live meshing preview: add a mating gear, watch the pair run, and read the exact centre distance and ratio off the panel.
- Practical print features built in: shaft bore, DIN-style keyway, lightening holes, and warnings for undercut or too-fine teeth.
- Download a watertight STL for 3D printing — free, no watermark — or a real-millimetre SVG / DXF for laser cutting and CAD.
- 100% in your browser: instant regeneration as you drag sliders, nothing uploaded, no account.
Process
How it works
- Set the tooth numbersPick the gear type, teeth and module (tooth size). The preview regenerates instantly and warns you if the combination undercuts or won’t print well.
- Check the meshShow the mating gear to see the pair run together, and note the centre distance — that is the exact shaft spacing your design needs.
- Download and makeExport STL for the printer, or SVG / DXF at true scale for a laser cutter or CAD. Two gears mesh when they share module and pressure angle.
The three numbers
Module, teeth and pressure angle — what actually defines a gear
The module is the tooth size: pitch diameter = module × teeth, and two gears only mesh if their modules match. (Working from an imperial chart? module = 25.4 ÷ DP.) The tooth count sets the ratio — a 20-tooth driving a 40-tooth halves the speed and doubles the torque. The pressure angle shapes the flank: 20° is today’s standard, 14.5° appears in older and hobby designs, 25° gives stubbier, stronger teeth that tolerate sloppy centre distances — common in 3D-printed gearboxes. Everything else — outside diameter, root, centre distance — follows from those three numbers, and the readouts show them all.
3D printing
How to 3D print gears that actually mesh
Keep the module at 1 mm or more with a 0.4 mm nozzle so each flank spans several extrusion widths. Add 0.1–0.2 mm of backlash — printed surfaces are slightly oversized, and a zero-backlash pair binds. Print gears flat on the bed with 100% infill or at least four walls, so layer lines run across the teeth instead of along them. For gearboxes, herringbone teeth run quieter than spur and cancel the axial thrust that pushes helical gears sideways. Below 17 teeth, add +0.3…+0.5 profile shift to avoid the undercut that weakens small pinions. Mount the pair at the centre distance in the readout, not “until it feels right”.
Notes
Good to know
- Tooth flanks are exact involutes; the root fillet is a close approximation of the true trochoid (it affects strength margins, not meshing).
- Helical and herringbone gears are exported as one twisted solid; the mate needs the opposite hand — generate it by swapping the tooth counts.
- The rack is straight-toothed (no helical rack), and internal ring gears assume an external spur/helical pinion.
- SVG and DXF export the 2D face profile — for helical gears the 2D outline is the transverse section, so laser-cut versions behave like spur gears.
FAQ
Questions, answered
Is this a true involute gear generator?
Yes. Tooth flanks are computed from the involute of the base circle with your module, pressure angle, profile shift and backlash — the same geometry CAD packages produce — plus an approximated root fillet. Gears made here mesh with any standard gear of the same module and pressure angle.
What is the module, and how does it relate to DP?
Module (mm) is the tooth size: pitch diameter = module × teeth. It is the metric equivalent of diametral pitch — module = 25.4 ÷ DP — so a 24 DP gear is roughly module 1.06.
How do I make two gears that mesh?
Give both the same module and pressure angle, choose tooth counts for your ratio, and mount them at the centre distance shown in the readout: module × (z1 + z2) ÷ 2 for external pairs. The preview shows the pair running so you can sanity-check before printing.
Can I download an STL for 3D printing?
Yes — the STL is a watertight solid in millimetres, with the bore, keyway and lightening holes already cut. Slice it flat with 100% infill or 4+ walls for strong teeth.
Can I laser-cut the gears?
Yes. SVG and DXF exports are true-scale millimetre outlines (the DXF is R12 with closed polylines) that open in LightBurn, Fusion 360, Illustrator or AutoCAD.
Why herringbone instead of helical?
Helical teeth engage gradually, so they run quieter than spur — but they push the shaft sideways (axial thrust). Herringbone joins two opposite helices, cancelling the thrust while keeping the smooth engagement; it prints without supports, which is why printed gearboxes love it.
What does the undercut warning mean?
Below about 17 teeth (at 20°), a standard cutter removes material from the tooth root, weakening it. Add positive profile shift (+0.3…+0.5) or more teeth; the warning disappears when the geometry is safe.
Next