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Pressure Angle

Related Links : 压力角 - 中文版

1-5 Pressure Angle

pressure angle 1

The pressure angle exists between the tooth profile and a radial line to its pitch point. In involute teeth, it is defined as the angle formed by the radial line and the line tangent to the profile at the pitch point. Here α = α’. Therefore, α’ is also the pressure angle.

pressure angle 2

  1. Normal to the profile
  2. Tangent to the reference circle
  3. Tangent to the profile
  4. Radial line

This figure indicates the meshing of a gear A and a gear B at the pitch point.

pressure angle 3

  1. Common normal
  2. Reference circle
  3. Reference circle

At the pitch point, the gear A is pushing the gear B. The pushing force acts along the common normal of the gear A and the gear B. The pressure angle can be described as the angle between the common normal and the line tangent to the reference circle.

(For reference)
The most common pressure angle is 20°. Formerly, a pressure angle of 14.5° was also used.

Related Links :
Gear Tooth Profile
Involute Tooth Profile
Spur Gears

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