Gears | Working pressure angle
The working pressure angle αw is the angle of inclination of the line of action between pinion and the wheel. It is measured relative to the perpendicular to the line connecting the centers of the pinion and wheel O1O2 (see figure). The line of contact is the tangent to the base circles of pinion and wheel. Consequently, the working pressure angle increases as the center distance between the two gears becomes larger, and decreases as the gear centers approach each other. The working pressure angle is always defined in the transverse plane, i.e., αw=αwt.
In general, the working pressure angle is not equal to the (manufacturing) pressure angle α (i.e., the working pressure angle between the gear and the generating rack). In the case of helical gears (β≠0), a distinction must also be made between the pressure angle in the transverse plane αt and in the normal plane αn. If the sum of the profile shifts of pinion and wheel is equal to zero, the working pressure angle αw is equal to the (manufacturing) pressure angle α.
