Gear Terminology

Gear terminology and properties have been developed through the years of evolution. The most widely used tooth form or profile is known as the 'involute' profile. The 'involute' is the locus of a point on a straight line, which rolls without slipping on the circumference of a circle.

Figure 3 Involute generation. (Marshek)

In the case of gear teeth the circle that the straight line rolls on is referred to as the base circle. The same involute profile is also generated by the end of a piece of string, which is unwrapped from the base circle.

Figure 4 shows some teeth with the most commonly used terms of description.

Figure 4 Gear definitions. (Marshek)