Pick the thread starts, module and wheel teeth. Get the ratio, lead angle, all dimensions, efficiency, whether the drive is self-locking, and the forces on the bearings.
| Dimension | Worm | Wheel |
|---|
Cylindrical worm drive with a 90° shaft angle, after DIN 3975. m is the axial module of the worm (equal to the transverse module of the wheel), z₁ the thread starts, z₂ the wheel teeth, q the diameter factor, αn = 20°, μ the friction coefficient.
Friction for hardened steel on bronze comes from a typical curve of μ against sliding speed for a well-lubricated drive (about 0.08 at 0.1 m/s, 0.045 at 1 m/s, 0.025 at 5 m/s). Cast iron runs about 30% higher, plastic wheels are set to 0.10. The self-locking check uses static friction (about 0.11 for steel on bronze), because a drive only locks while it stands still. Running efficiency uses the friction at the actual sliding speed. Worm length and wheel face width use common design rules; check the gear maker's data.