Involute spur gear: parametric template

Parameters

Open in the editor opens the design with these defaults; change them afterwards in Modify › Parameters, and everything that depends on them follows. Opened from the editor’s template library instead (New ▾ › New from template…), the template asks for its values first and checks them against these ranges and against each other, and Copy link gives an address that opens it with your values.

Name	What it sets	Default	Range
`module`	Module	2 mm	0.5 to 5 mm, steps of 0.25
`teeth`	Number of teeth	20	10 to 80, steps of 1
`pressureAngle`	Pressure angle	20 deg	14.5 to 25 deg, steps of 0.5
`faceWidth`	Face width	8 mm	2 to 40 mm, steps of 0.5
`bore`	Bore diameter	5 mm	1 to 30 mm, steps of 0.5

Notes

Change the module and the number of teeth together to get the size you want: the pitch diameter is module x teeth, the outside diameter module x (teeth + 2), and two gears mesh when they share the module and the pressure angle (20 degrees is the standard; 14.5 is the old one). The centre distance of a pair is module x (teeth1 + teeth2) / 2.

The flanks are true involutes (a spline through twelve points on each, within 0.0004 module of the curve) with a root fillet of 0.25 module; teeth are not undercut, so below about 17 teeth at 20 degrees the mating gear's tips may touch the flank near the root - give a little extra centre distance or use more teeth. There is no backlash built in: for 3D printing add 0.1 to 0.2 mm to the centre distance, and break the tip edges with a small chamfer if your printer flares the first layer.

The bore is limited automatically so that at least one module (or 1 mm) of rim stays under the teeth. For a D-shaft or a key, sketch it on the face and cut it. The tooth count drives a sketch pattern, so the whole outline is one extrusion: even 80 teeth regenerate in a few seconds.