What does a pressure angle in a gear physically mean?
Pressure angle is in general the angle at a pitch point between the line of pressure which is normal to the tooth surface, and the plane tangent to the pitch surface. The pressure angle gives the direction of the normal to the tooth profile. The pressure angle is equal to the profile angle at the standard pitch circle and can be termed the “standard” pressure angle at that point. Standard values include 14.5, 20 and 25 degrees.
Meshed gears must share the same pressure angle to perform efficiently and wear properly. The tooth surfaces of meshed gears roll against each other and create a force driving the gears apart. Selecting a suitable pressure angle and number of teeth that applies for both meshed gears best takes advantage of the strength of the materials for the torque that is to be transmitted.
