The profile is a true involute: not a star with teeth, but the curve that makes two wheels turn at a constant ratio. Two wheels mesh when they share the same module.
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The tooth is not a rounded triangle: it is the curve that keeps the ratio constant as the wheels turn. Two wheels with the same module mesh, and that is all there is to it.
For two wheels of z₁ and z₂ teeth with module m, the centres sit m·(z₁+z₂)/2 apart. It is written below while you move the sliders.
A plain DXF on the usual layers. Lightburn, xTool, Glowforge: it opens where you already work.
The module is the measure gears are spoken of in: it is the pitch diameter divided by the number of teeth. Two wheels mesh only if they share a module — the tooth count sets the ratio, and so how much one slows the other down.
For 3 mm plywood a module between 2 and 4 gives sturdy teeth that do not chip on the cut. Below 2 the teeth get as thin as a matchstick and the laser eats part of them.
Twenty degrees is the standard and is almost always right. Lower makes the motion smoother but the teeth more fragile; higher strengthens them and makes the movement a little harsher.
Tick «first wheel as a ring gear» and the teeth turn toward the centre: the small wheel goes INSIDE and turns the same way, not against it. The centres come closer instead of further apart — m·(z₁−z₂)/2 — and this is the part planetary reducers and rotating bezels are made of. Leave about a dozen teeth of difference between ring and wheel: below that the tooth tips foul each other.
Yes: download twice with the same module and different tooth counts, or open the project in the full editor and duplicate the wheel with a different count.
