Gear generator: spur gears as STL, free in your browser

How to use it

1. Choose a ready-made gear under Start from, or set the module and the teeth yourself.
2. Under Body and axle, set the thickness, the bore for your axle and, if you like, a hub.
3. Drag in the 3D view to look round it. The figures under the settings give the pitch, tip and root diameters.
4. Press Download STL and open it in your slicer. It lies flat, ready to print.

Module, teeth and the sizes that follow

Two gears mesh when they have the same module and the same pressure angle. The module is the size of a tooth: the pitch diameter divided by the number of teeth. From the module m and the teeth z everything else follows:

• Pitch diameter: d = m × z
• Tip diameter: m × (z + 2)
• Root diameter: m × (z − 2.5)
• Distance between the axles of two gears: m × (z₁ + z₂) / 2
• Gear ratio: z₂ / z₁

A module 1 gear with 20 teeth is 20 mm across its pitch circle and 22 mm over its tips; paired with a 40-tooth gear the axles stand 30 mm apart.

Printing gears that work

• Module 1 or more prints well on an FDM printer with a 0.4 mm nozzle; finer gears (0.5) are a job for a resin printer.
• Backlash of 0.1 to 0.2 mm keeps printed teeth from binding. Raise it if your gears stick, lower it if they rattle.
• Below about 17 teeth at 20° a real gear is undercut at the root. It still meshes, but the teeth are weaker: use a 25° pressure angle or more teeth for a small pinion that has to work hard.
• Make the bore a tenth or two larger than the axle, or drill it out after printing.
• PETG and nylon wear better than PLA in gears that run for a long time.

Questions

Is the gear generator free?

Yes. Try as many gears as you like without an account. To download the STL you get a link by mail, which makes your free WAZO3D account at the same time; members download straight away. The full WAZO3D editor is free too, with a free account.

Are the teeth real involute teeth?

Yes. The flanks are involute curves worked out from the base circle, at a pressure angle of 14.5°, 20° or 25°, so the gears roll on each other as real gears do.

Which two gears mesh?

Any two with the same module and the same pressure angle. The number of teeth sets the ratio; the distance between the axles is the module times the sum of the teeth, halved.

Which file formats can I get?

The STL comes from this page. Opened in the WAZO3D editor, the gear can also be exported as STL, OBJ, glTF and more, and combined with other parts.

Can I make worm gears, racks or helical gears?

Not yet: this generator makes spur gears. In the editor you can build a rack or a housing round the gears yourself.