What is a Worm Gear?

With RS worm and wheel gears, you can produce controlled, high-torque actuation in a very small space using minimal input torque. Learn the advantages they offer over bevel gears and rack and pinion gear sets - though we can help with those too.

Worm gears may appear to be just simple screws, but their threads are hard-working gear teeth for turning worm wheel gears. Worm and wheel gears produce massive torque increases in their driven gears. They fit into very tight spaces, making them versatile, powerful tools for their small size.

These worm and pinion gears have many industrial uses such as conveyor belts, lifts, and gates, as well as everyday applications like vehicle odometers and even tuning guitars.

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How Does a Worm Gear Work?

If you’ve ever watched an auger spin, its threads seem to continuously travel lengthwise, ‘disappear’ and get replenished. A worm gear makes this ongoing train of threads a steady motion of gear teeth for making a worm wheel rotate. This turns spinning into straight movement and then right back into rotation.

This conversion produces a drastic change in the speed and torque of the two gears. The worm wheel will crawl compared to the gear that looks like a worm, but it’ll make up for that slow speed with skyrocketing torque. So, the output shaft will do more work than the input shaft does, it just takes longer to do it - a more than reasonable trade-off in many industries.

If you manually spin a worm wheel, the mechanism jams. These gears self-lock due to the way their teeth mesh. When it comes to machinery design, this can be a boon since you can depend on the driven shaft to rotate only when needed. Other gear sets using only round gears often require separate backstops to achieve this.

Friction and lubrication must not be overlooked in worm gear installations. The sliding way these gear teeth surfaces mesh drives friction up and wipes away lubricant. Leaving the gears dry for too long leads to heat, wear, and inefficiency, so make a healthy oil regimen part of your system maintenance.

At RS, our worm gears are made of carbon steel coated with black oxide, and our worm wheels are bronze. Worm wheels are often more accessible for replacement. Their soft bronze will take the brunt of the wear in the gears’ frictional relationship, but these gears will often be well placed for replacement.

Types of Gear

Along with worm gear sets, our gear and rack products include bevel gears, pinion gears, and gear racks.

Bevel Gears

Bevel gears transfer rotation between two rotating shafts set up at 90 degrees to each other. Their teeth are cut at 45 degrees in a circular pattern to make this happen, giving these gears cone shapes. Bevel gears are found in applications like food packaging machines, lawn and garden equipment, and machining tools.

Gear Racks

A gear rack is basically a long, flat track of gear teeth. It is driven by a pinion gear, which produces a long, controlled horizontal movement.

Spur Gears

Spur gears, also known as pinions, have teeth cut parallel to their driving shaft. They are thus meant to mesh with gears parallel to their orientation. The driven gears can be varied sizes of other gears with parallel teeth or gear racks.

Difference Between Worm Gear and Rack and Pinion

The driving gear in a rack and pinion set is the pinion gear, which drives the horizontal rack. The rack also has a finite, constrained length to travel within. In contrast, a worm gear can spin and drive infinitely in its small space.

Applications of rack and pinion gear sets include lifting mechanisms, valve control, and steering systems. Though pinion gears look similar to worm wheels, they differ in their materials and tooth shape. Pinion gears are the driving gears, like worm gears, so they too come in black oxide-finished carbon steel to last longer under their loads. Worm wheels have circular cut teeth for meshing with worm gears, while pinion gear teeth have straight edges.

There is no self-locking in these sets since the gear rack can actually drive the pinion. For this reason, consider installing backstop devices to prevent the rack from running away from you!

Worm Gear Uses and How to Install Them

To install an RS worm gear, first, ensure it’s matched to the correct diameter shaft.

All our worm gears are supplied with an M4 G/S set screw that threads through a small bore in the worm gear’s threads and into its centre bore. Ensure this set screw isn’t protruding into the centre bore and position the worm gear at the desired spot on the shaft. Tighten the set screw onto the shaft to fully set the worm gear’s position.

Worm gear sets are handy in a tight spot since they take up so little space. They can even be set up so that one set’s worm wheel drives another worm gear, and so on, as seen with odometers.

How to Calculate the Gear Ratio of a Worm Gear

It’s simple to figure out the worm gear ratio - you just count teeth, as with other gears. Review our gear spec sheets for the number of threads on the worm gear and teeth on the worm wheel. A single thread is a continuous track travelling around the worm gear's length.

With only one thread on the worm gear and 40 teeth on its worm wheel, the worm gear ratio is 1:40. The worm wheel will lag far behind the worm gear, spinning 40 times slower than its driver.

Unfortunately, you won’t get torque gain by a factor of 40, though. While this would be great, the torque increase depends on more detailed factors like lubricant, wear, and thread profiles.

If these worm and wheel gears look like they can mesh well with your application, RS is here to meet your needs.

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