Advantages of cylindrical keys for torque transmission

Abstract

Elastic stresses due to torque transmission through cylindrical keys have been determined from 16 two-dimensional photoelastic tests. Two key diameters were tested with dry and lubricated shafts, using keys which were push or sliding fit, dry or lubricated. The greatest stresses occur in the keyway surface of the shaft at the loaded edge of the keyway and about one-third of the way around the keyway. The total torque is transmitted partly by friction and partly through the key. The latter has been used to calculate the mean shear stresses across the key. The peak stresses are independent of the key diameter, shaft lubrication and key surface condition; unlike rectangular keys, they vary little with torque. Peak stresses are lower than in rectangular keys.