Products > Spur Gears

Spur Gears

Spur Gear produced by Arrow Gear
Spur gear

While widely known for our bevel gear products, Arrow is also a leading supplier of spur gears.

Spur gears, sometimes referred to as straight-cut gears, are perhaps the most common form of parallel axis gear.

The spur gear has a cylindrical shape with teeth cut parallel to the axis. The most common spur gears are external gears, where the teeth are located on the outside of the cylinder. Another variation is internal spur gears where the teeth are cut on the inside of the cylinder. In either case, spur gears are designed to mesh with mating parts located on parallel shafts.

The teeth projecting from a spur gear are not straight-sided, as this would not allow for uniform motion. Instead, the tooth surfaces of the gear teeth have an involute profile.

Animation Showing Involute Profile
This animation shows two involute gears rotating in mesh, with the left driving the right. The blue arrows show the contact forces between the two gears.

Involute profile is a critical attribute in the forming of the gear teeth, and the involute gear profile is the most common system used in modern gearing.

Gears that utilize involute profiles have tooth surfaces that are involutes of a circle. A good way to explain the involute of a circle is to imagine a string wrapped around the outside diameter of a circle. As the string unwinds from the circle, a fixed point on the string creates a spiraling curve. The spiraling curve is an involute and is the same profile as a gear tooth. See Fig.1

The physical properties of the involute profile result in minimal speed or torque variations as the mating pairs of teeth come in and out of mesh.

Animation Showing Involute Principle
Fig.1 - This animation shows the basic principle of how an
involute profile is formed.

Arrow began robust investment in spur gear technologies over 30 years ago. Today, Arrow is equipped with a full range of advanced machine tools for the shaping, hobbing, grinding, and inspection of spur gears.  Arrow’s spur gear products are now utilized in a wide range of both aerospace and commercial applications.

Recently, Arrow expanded size capabilities for spur gears up to 36 inches by adding new equipment including the Hofler Rapid 800 Spur and Helical Tooth Grinder.

Spur Gear Teeth produced by Arrow Gear
Spur gear teeth

Arrow’s size range and capabilities for Spur Gears are provided in the list below.

Maximum Pitch Diameter – 36”
Diametral Pitch – 3.0 – 48
Face Width – 13.0
Unground Tooth – AGMA Q9
Ground Tooth – AGMA Q13

Pump Gears

Pump Gear produced by Arrow Gear
Pump gear
Pump Gear produced by Arrow Gear
Pump gear

Pump gears are similar to spur gears in their geometry. However, pump gears are not used to transmit power between shafts. Instead, they are used for the positive displacement of fluid in pumping applications - most commonly for fuel systems. The benefit of using pump gears in this application over other methods is the precise volume of fluid that is displaced
during each revolution.