Worm drive

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It has been suggested that this article or section be merged into worm gear. (Discuss)

Worm Drive is also a computing term; see Write Once Read Many

A worm drive consists of a cylinder with a spiral groove mounted on a shaft. A gear meshes with the spiral groove on the cylinder, and when the cylinder rotates, it causes the gear to rotate also.

A worm drive controlling a wier gate. Position of the gate will not change after being set

A worm drive produces a large gearing ratio in a compact size. For every rotation of the worm gear shaft, the output radial gear rotates by only 1 tooth. The output drive shaft is at 90 degrees to the input shaft.

The worm gear is always the one that is driven, with the output taken from the radial gear. The arrangement will not readily work in reverse. If torque is applied to the radial gear the worm gear will often not rotate due to the shallow angle of the worm gear helix, with the majority of the force acting axially along the worm gear shaft. This will often cause the worm gear to move on the shaft if it is not securely fixed (such as with plastic friction fit worm gears) or can cause damage to the gear teeth if sufficient force is applied. The resistance to reverse driving is useful in some applications, where the mechanism will stay in the position set without power applied to the driving motor.

Plastic worm gears are often used on small battery operated electric motors, to provide an output with a lower angular velocity (fewer revolutions per minute) than that of the motor, which operates best at a fairly high speed. This motor-worm-gear drive system is often used in toys and other small electrical devices.

A worm drive is used on jubilee type hose clamps, the tightening screw has a worm thread which engages with a slots on the clamp band.