Gear module explained: choosing a module for 3D printing and DIY

What is the module?

The module (m, in mm) is the key parameter of a metric gear: pitch diameter divided by the number of teeth. A larger module means bigger, thicker, stronger teeth; a smaller module gives finer teeth that run smoothly but carry less load.

m = D / z　　D = m · z　　p = π · m

D is the pitch diameter, z the tooth count and p the circular pitch. Standard whole depth is 2.25 m: addendum 1 m, dedendum 1.25 m.

Different modules don't mesh

Two gears mesh only if their circular pitch — i.e. their module — and their pressure angle (usually 20°) match. A m1 gear will not run with a m1.5 gear or rack, even if the diameters look similar.

TIPImperial gears use diametral pitch DP (teeth per inch of pitch diameter): m = 25.4 / DP. 32 DP ≈ m0.794, not m0.8.

Common modules at a glance

Module advice for 3D-printed gears

• FDM (0.4 mm nozzle): use m ≥ 1. Below m0.8 the tooth details are smaller than two extrusion widths.
• SLA / DLP resin: m0.5 or even m0.3 works, with smooth flanks for small precise mechanisms.
• SLS / MJF nylon: m0.8 and up — tough, wear-resistant functional gearboxes.
• Face width is typically 6–10 × module; for more load increase the module before the width.

Add 0.05–0.15 mm of backlash so printed gears don't bind, and open bores by 0.1–0.2 mm. The spur gear generator has an FDM print-fit preset.

Centre distance from the module

a = m · (z₁ + z₂) / 2

For m2 with 20 and 40 teeth: a = 2 × 60 / 2 = 60 mm. Profile-shifted gears change this — use the spur gear centre distance calculator.