Worm drive

A worm screw driving a worm wheel at 90° — high reduction.

A worm drive meshes a worm (a driving screw) with a worm wheel at 90°. One worm turn advances the wheel by its number of thread starts, so the reduction is wheel teeth ÷ starts (for example 30:1 from a single-start worm and a 30-tooth wheel) — and it’s often self-locking, meaning the wheel can’t back-drive the worm. The worm lies horizontal and the wheel stands on the plate, positioned so their pitch surfaces are tangent. Both are separate editable bodies.

Print the pair? Turn on the hobbed (throated) wheel. Left plain, the wheel is an ordinary helical gear whose teeth run straight across its face. It is set with its teeth in the worm’s grooves, so the pair clears both as placed and as it turns. A real worm wheel is *throated*: hobbed concave so its teeth wrap around the worm. Switching it on cuts the wheel exactly that way, with the teeth still engaged to drive. It is off by default only because it is slow to rebuild — the cutter is one worm per step per tooth — so leave it off while you are still adjusting numbers, and switch it on when you mean to print. Above 40 wheel teeth it is skipped, because the cutter would grow large enough to stall the geometry worker.

1. Open the Generate panel from the left sidebar and choose Worm drive (under Gears & drives).
2. The worm and wheel drop in on crossed axes, meshed. The parameters open in the Properties panel, where you set them.
3. Set the module, worm diameter, thread starts, and worm wheel tooth count.
4. Set the pressure angle, worm length, wheel thickness, and bore.
5. Turn on Hobbed (throated) wheel before you print — without it the pair cannot be assembled.