3D PRINTED SPUR GEAR GUIDE
Make gears that
actually mesh.
Most problems start with mismatched basic geometry.
MODULE
Matching gears need the same tooth size.
Module describes the size of metric gear teeth. Two spur gears intended to mesh should use the same module and normally the same pressure angle. Pitch diameter is approximately the module multiplied by the number of teeth, so a 20-tooth module-2 gear has a pitch diameter of about 40 mm.
Changing tooth count changes the gear diameter and the ratio. A 20-tooth driving gear turning a 40-tooth driven gear gives a 2:1 reduction: the driven gear turns at half the speed and roughly doubles torque before losses.
PRESSURE ANGLE
20° is a common modern starting point.
The pressure angle affects the shape of the involute tooth and how force is transmitted. Common values include 14.5°, 20° and 25°. Gears with different pressure angles should not be treated as a matched pair even when the module is the same.
Very small tooth counts can also suffer from undercut or weak tooth roots. For functional printed gears, larger modules and sensible tooth counts are usually more forgiving than very fine teeth.
3D PRINTING
Allow for the real printer.
A mathematically perfect gear can still bind after printing. Extrusion width, elephant's foot, material shrinkage and printer calibration all affect the final size. Add appropriate centre-distance or tooth-clearance allowance for your process, and avoid an overly tight bore unless you plan to drill or ream it afterwards.
For load-bearing parts, print orientation, layer adhesion and material choice matter as much as the tooth geometry. Treat a generated SVG as the starting geometry, then validate the finished part in the actual mechanism.