A worm gear set actually looks a lot like it sounds — there's a worm that drives a gear. The worm — a shaft with a spiral thread — engages with and drives the gear — a toothed wheel. The worm screw and worm wheel are aligned at a 90-degree angle, forming the simplest kind of right angle gearbox. In fact, a worm gear was one of the original six simple machines. No matter how simple, though, the worm gear is an effective, time-honored way to manage power and torque.
Uses for Worm Gears
Worm drives create a compact means to substantially decrease speed and increase torque. A worm gear can have a massive reduction ratio with little effort — by simply adding more circumference to the wheel. That technique can either greatly increase the torque, or greatly reduce the speed. By comparison, it would take multiple reductions of a conventional gear set to achieve the same results — so worm gears have fewer moving parts and fewer places for failure.
Another major reason to use a worm gear is its inability to reverse the direction of power. In many ways, that makes it a self-locking mechanism. Because of the friction between the worm and the wheel, it is virtually impossible for a wheel with force applied to it to start the worm moving. On a standard gear, the input and output can be turned independently once enough force is applied. That requires adding a backstop to a standard gearbox, further increasing the complication of the gear set.
Ideal Applications for Worm Gears
Worm gears are used in low to moderate horsepower applications. They offer low initial cost, high ratios, and high output torque in a small package. You should consider using worm gears in these situations:
- A high ratio is needed in a compact package.
Worm gears can have a low number of threads, so higher ratios can be accomplished with fewer gears. - Quiet operation is required.
The sliding action of worm gears is quieter than other gear types. - When back driving is not desirable.
Since worm gears only work in one direction, their self-locking characteristics aid braking and avoid back driving.
Worm gears are less efficient than most other gear combinations. Their typical efficiency ranges from 50-90%, depending on gear ratio, lead angle, and friction factor. For comparison, helical gears range from 94-98% efficiency, while the efficiency of spiral bevel gears ranges from 95-99%.
Worm Gears from W.C. Branham
The three model configurations of W.C. Branham Series 4 Right Angle Worm Gearboxes include: Hollow Bore, Single Shaft; Hollow Bores Only; and Hollow Bore, Double Shafts. All come in 10:1 and 20:1 ratios.
Select models are available with .625 inch diameter shaft x either .625, .750, 1.00 inch diameter hollow bores. Each model is designed around a 1.333-inch center distance, and all models are constructed with double sealed, heavy duty ball bearings and case hardened worm gears.
