What’s a worm winch?

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A worm gear winch uses a worm gear and a disc-shaped flat gear to create torque, resulting in a higher gear ratio than other winches. This design is less efficient but preferable for fast-acting self-locking winches, commonly used for boat trailers, low-bed car transport equipment, and tow trucks.

A worm gear winch uses a specialized type of helical gear called a worm gear to create torque. The worm gear is connected to a drum that spins as the gear rotates. These winches are available in hand crank and motorized versions. Thanks to the worm gear winch design, it has a higher gear ratio than other winches of a comparable size.
Worm gears use a worm and a disc-shaped flat gear. Worms are long spur gears that may have a single tooth or multiple teeth that spiral around the worm at an angle. This creates the look of a screw. The worm intersects the flat gear at an angle that allows the worm teeth to mesh loosely with the gear teeth. Depending on the angle of the intersecting teeth, the set may be self-locking, meaning the worm can turn the gear but the friction will not allow the gear to turn the worm.

The high gear ratio of the worm winch makes this design perform its role faster than other designs. While the traditional helical gear has a gear ratio of 10:1 or less, worm gears increase that ratio to 500:1. This equates to faster movement because each rotation of the worm rotates the gear 500 times compared to the 10 revolutions generated by traditional helical gears.

While the worm gear’s high ratio makes it run faster than other gear sets, the trade-off is efficiency. The worm gear design leaves a large amount of backlash, or sliding action, between the teeth of the two gears. In some cases, the worm winch is less than 50% efficient. Despite this drawback, the worm assembly is preferable for applications where fast-acting self-locking winches are required.

A common application for a worm gear winch is boat trailers. The worm winch is usually mounted on the front of the trailer and the drum is loaded with braided wire rope or cable. The boat is connected to the winch cable, then the operator operates the handle or operates the electric motor connected to the worm. As the worm begins to spin, its teeth connect with the gear, turning the drum and pulling the boat onto the trailer. Similar arrangements are used for low-bed car transport equipment and tow trucks.

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