Pressure Angle (α)
The pressure angle α is the angle between the line of action (force direction between meshing tooth flanks) and the tangent to the operating pitch circle at the pitch point. The standard value is 20° per DIN 867; it influences load capacity, tooth shape, and the radial forces acting on the bearings.
Definition and Standard Value
For involute gearing, the pressure angle is also the flank angle of the basic rack profile. The standard value of 20° per DIN 867 is a compromise: it provides sufficient root thickness, moderate radial force on the bearings, and good manufacturing properties. A smaller angle (14.5° in older standards) yields slimmer, quieter teeth with higher contact ratio but lower load capacity. A larger angle (25°) increases load capacity and reduces the risk of undercut but generates higher bearing forces.
Comparison of Common Pressure Angles
| Pressure angle | Load capacity | Contact ratio | Bearing force | Typical application |
|---|---|---|---|---|
| 14.5° | Low | High | Low | Older standards, precision mechanics |
| 20° | Standard | Medium | Medium | General mechanical engineering (DIN 867) |
| 25° | High | Low | Higher | High-performance gearboxes, low tooth counts |
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