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A keyway acts as a notch: it lowers the torsional strength of the shaft and increases the angle of twist. Moore's empirical equations give both as ratios against a shaft with no keyway. Multiply the allowable torsional stress for a plain shaft by the strength ratio and you have the allowable torsional stress with the keyway.
Input
Shaft diameter
Keyway width
Keyway depth
Allowable torsional stress (without keyway)
Result
Strength ratio
Ratio of angles of twist
Allowable torsional stress (with keyway)
Notes
- Both ratios are dimensionless: they depend only on the shaft diameter and the width and depth of the keyway. Enter all three in the same unit.
- The equations are empirical, so they hold for keyways of ordinary proportions. A groove that is unusually deep or wide will take the result away from reality.
- Source: Hyojun Kikai Sekkei Zuhyo Binran, 5th revised and enlarged edition, Fujio Oguri and Tatsuo Oguri, Kyoritsu Shuppan, p. 13-5, 2005.