wormdrive

Wormdrive is a gear arrangement consisting of a screw-like worm and a wheel, called the worm wheel. The worm is mounted on one shaft and the worm wheel on a second shaft whose axis is approximately perpendicular to the worm’s axis. When the worm turns, its helical thread engages the teeth of the worm wheel, producing rotation of the wheel in a compact, high-reduction configuration.

The gear ratio is roughly Z/S, where Z is the number of teeth on the worm wheel and S is the number of starts on the worm. A single-start worm with a wheel of Z teeth yields a 1:Z reduction, while multi-start worms produce smaller or larger reductions according to S. This arrangement is favored when large reductions are needed in a compact space.

Characteristics include smooth, quiet operation and a high gear reduction in a small footprint. Under certain conditions—typically a low lead angle and sufficient friction—the system can be self-locking, meaning back-driving is resisted. However, efficiency is limited by sliding contact between the worm and wheel, leading to heat generation under heavy loads. Proper lubrication and precise alignment are essential to minimize wear and backlashes.

Applications span actuation systems, machine tools, lifting mechanisms, conveyors, and robotics, where a compact, high-reduction drive is advantageous. Design considerations include material pairing (often hardened steel for the worm and bronze or steel for the wheel), surface finish, lubrication regime, and backlash control to ensure reliable operation over time.