Worm gears work like a screw, with “teeth” that form a continuous helix. Worm gears are not necessarily the most efficient choice, but for certain industrial applications, they offer distinct advantages.
A worm drive consists of a screw (the worm) that meshes with a gear or wheel. This design enables:
- Control over rotational direction and speed
- Higher torque transmission
Types of worm gears
There are three basic work drive designs:
- Non-throated. Instead of a continuous thread, this style has a single moving point that contacts the gear. The minimal contact makes this type of worm drive most vulnerable to wear and tear from high unit load.
- Single-throated. This variation can withstand high unit loads with less wear. Its concave helix wraps around the worm, making continuous contact with the gear.
- Double-throated (called hourglass or cone). This style can withstand the highest unit loads without excessive wear and tear, because it has concave teeth on both the worm and the gear, doubling the contact area.
Worm drives can be designed with right-hand or left-hand gearing, to turn either clockwise or counter-clockwise. With an internal helical gear, both parts must be the same hand. With external helical gears that function in parallel, the hands must be opposite.
The simplest of worm gears is the peg that turns to tune an acoustic guitar. This is the only type of worm gear that allows bi-directional turning. The drives used in industrial applications do not reverse, making them valuable to regulate speed and when braking and/or holding are required. Good examples are elevators and other lifting mechanisms. For these applications, a worm drive is not used alone, but as a secondary braking system.
Because the worm drive’s non-reversing characteristic enables holding, it is also commonly used to operate gates and conveyor systems to prevent equipment from moving backward. In applications where equipment must move in both directions – such as an automatic security gate – two worm gears are installed, one to control each direction. Security is enhanced because the gate cannot be breached or forced open.
Worm drives are compact, which makes them useful in designs where space is limited. This is often the case with conveyors, small machinery, and packaging equipment. They also operate quietly compared to other gear types, making them ideal for installations where noise would pose problems, such as elevators and theaters.
Another significant advantage is the worm gear’s ability to transmit torque in 90o.
W.C. Branham manufactures three types of right angle (worm drive) gearboxes, and each model can be spec’d in numerous bore sizes and gear ratios.
As always, if you need help determining which configuration would be best for your application, we enocurage you to contact W.C. Branham's design and engineering experts.