<P> Pressure angle in relation to gear teeth, also known as the angle of obliquity, is the angle between the tooth face and the gear wheel tangent . It is more precisely 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 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 are 14.5, 20 and 25 degrees . Earlier gears with pressure angle 14.5 were commonly used because the cosine is larger for a smaller angle, providing more power transmission and less pressure on the bearing; however, teeth with smaller pressure angles are weaker . To run gears together properly their pressure angles must be matched . </P> <P> The pressure angle is also the angle of the sides of the trapezoidal teeth on the corresponding rack . The force transmitted during the mating of gear teeth acts along the normal . This force has components along the pitch line and the other along the line perpendicular to the pitch line . The force along the pitch line which is responsible for power transmission is proportional to the cosine of pressure angle . The one which exerts thrust (perpendicular to the pitch line) is proportional to the sine of pressure angle . So it is advised to keep the pressure angle low . Standard pressure values are 14.5 and 20 degrees . </P>

How to determine the pressure angle of a gear
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