Wormwiel

Wormwiel, or worm gear, is a two-part gear arrangement that transmits torque between non-parallel shafts at approximately a right angle. It comprises a cylindrical worm (a screw-like gear) and a wheel with a helical tooth pattern (the worm wheel). The worm engages the wheel by sliding contact along its threads, causing the wheel to rotate in response to the worm’s turning.

Mechanics and ratio: The overall reduction is determined by the wheel’s number of teeth Z and the worm’s number of starts s. The reduction ratio i = Z/s. A single-start worm with Z teeth yields i = Z:1. Using multiple starts reduces the ratio for the same wheel; a given wheel can thus support different reductions by selecting a worm with different s.

Construction and materials: The wheel is typically bronze or brass to provide good wear characteristics against steel or hardened worms; the worm is usually steel, sometimes coated. Plastic versions use nylon or other polymers for light-load applications. Lubrication is essential to reduce wear, heat, and to maintain efficiency.

Performance and limitations: Worm gear sets offer high torque in a compact form and can provide self-locking under suitable lead angles, which prevents backdriving. However, efficiency is generally lower than spur gears due to sliding friction, and performance depends on lubrication, alignment, and load. They require precise manufacturing and can be sensitive to shock.

Applications and history: Used in actuators, machine tools, hoists, elevators, conveyors, and some automotive and aerospace systems, where right-angle drive, high reduction, or self-locking are desirable. The concept dates to the 18th–19th centuries and remains common in modern gear trains.