In a workpiece support, a servomotor, a right-angle speed reducer and a work gripping device are supported on a horizontal shaft which is rotatable on bearings in a frame to tilt the axis of rotation of the workpiece. The shaft is locked against rotation by a lever-operated screw, which exerts a lateral force on the shaft through a lock ring. The lock ring is held against rotation by a pin which is fixed to the frame and which extends into a hole in the lock ring along an axis parallel to the axis of the screw. Fixing the lock ring against rotation prevents unintended movement of the shaft caused by tightening of the lever-operated screw. The inner surface of the lock ring is provided with an axial extending V-shaped groove which engages a spacer ring fixed on the shaft along two lines of contact for secure locking of the shaft against rotation.