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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Some articles on pressure angle:

Profile Angle
... The profile angle of a gear is the angle at a specified pitch point between a line tangent to a tooth surface and the line normal to the pitch surface (which is a ... The profile angle gives the direction of the tangent to a tooth profile ... are considered only in a transverse plane, and the general terms profile angle and pressure angle are customarily used rather than transverse profile angle and transverse pressure angle ...
Backlash (engineering) - Gears
... in profile, pitch, tooth thickness, helix angle and center distance, and runout ... = difference between actual and ideal operating center distances = pressure angle Standard practice is to make allowance for half the backlash in the tooth thickness of each gear ... The amount of additional material removed when making the gears depends on the pressure angle of the teeth ...
Geared - Nomenclature - General Nomenclature
... Line of action, pressure line Line along which the force between two meshing gear teeth is directed ... position on the gear where the circular tooth thickness, pressure angle and helix angles are defined ... predefined diametral position on the gear where the circular tooth thickness, pressure angle and helix angles are defined ...

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