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A worm-gear motor consists of three parts: a threaded gear formed like a screw, an interlocking toothed wheel, and a motor to drive the gear. The worm gear translates the torque of the motor, driving it to a shaft attached to the wheel. Though the rotational speed of the shaft is less than that of the gear, its torque is greater, and the motor doesn't have to work as hard to produce it. Consequently, a worm-gear motor magnifies the rotational force of the motor that drives the gear. The spectrum of applications for a worm-gear motor extends from heavy industry and shipping to precision tuning for musical instruments and toys.
The force required to drive the wheel of a worm-gear motor depends on a number of factors, including the diameters of the wheel and screw, the number of threads in the screw, their angle of inclination, and the number of teeth in the wheel. The efficiency of the gear motor and its rotational speed are affected by the friction generated at the interface of the gear and the wheel, so a worm-gear motor needs to be frequently lubricated. It is self-locking; that is, the gear cannot be driven by rotating the wheel if this friction is too great. The angle of inclination of the threads is the main determinant of this friction.
The heavy uses of a worm-gear motor include presses and rolling mills used in the steel industry, as well as ship propellers and rudders. Elevator and escalator manufacturers use self-locking worm-gear motors to drive the devices because of the amount of torque they generate and also because they cannot be operated in reverse. In conveyance engineering, a worm-gear motor is used to drive conveyors in automobile, aircraft, and other factories that have assembly lines.
Smaller tools, appliances, and toys may also be powered by a worm-gear motor. A worm-drive circular saw is the tool of choice for builders and carpenters working in heavy construction because of the extra cutting power it provides, and home mixers employ a worm-gear motor to reduce their power requirements. Anyone familiar with the operation of a music box will recognize the operation of the hand-operated worm-gear motor that drives it, and small plastic worm-gear motors often power small toys. In addition, the tuning pegs on stringed musical instruments like guitars, banjos, and mandolins have a worm-gear drive that allows the musician to precisely tune the instrument while exerting a minimum of force.