What is pressure angle?

Pressure Angle

Pressure angle in relation to gear teeth, also known as the angle of obliquity, 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 angle formed by the common tangent to pitch circle and common tangent to Dedenda Circle throughout the pitch point is known as Pressure Angle. 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 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.

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