Overview of Various Gear Types, Part 1

When you think of a gear, this is the one that typically comes to mind. A spur gear transfers power and speed, while allowing for change in the ratio, speed, or rotational direction. Two spur gears may function on the same shaft at either the same or different rates. Spur gears are used for linear motion applications. They are found in anything from appliances and to aircraft and missile targeting systems. While they are simple and efficient in design, spur gears are relatively noisy due to their straight teeth.

A helical gear is very similar to a spur gear, however the tooth from one side to the other side is at an angle. If you looked at one head-on, you would see the angle. This angle allows for more contact on the tooth, which reduces both noise and vibration. Helical gears are more durable than spur gears due to the load being spread out across the larger surface area of the teeth. These attributes make them ideal for applications that require efficient transfer of motion and speed such as automotive transmissions, industrial machinery, and robotics. 

This type is somewhat different than spur and helical gears. It’s comprised of two components: the rack, and the pinion. The rack is essentially an “unrolled” gear that has teeth along a straight bar, allowing for back-and-forth linear motion. Racks have a straight-edged tooth profile, with a tooth that is very square when compared to the involute profile of a spur gear. The pinion is a circular gear that interacts with the rack. The most common usage example is a car’s steering system, where the rotational motion of a steering wheel is converted to the linear motion required to turn the wheels.  Rack and pinion gears are also found in lifting mechanisms where vertical movement is required such as CNC lathes or airplane interiors, to move things like trays and TV screens.

This is essentially the opposite of a spur gear. With an internal gear, the teeth are on the inside. These gears are ideal for situations where space is limited. They provide both low vibration and high speed reduction ratio. As such, they are most commonly used for planetary gear transmissions. They may be found in an extensive array of applications such as robotics, turbine generators, and inventory movement systems.