Abstract: A rotary drill bit for hand-held power drills comprises successively, a cutting section of progressively increasing diameter, a section of decreasing diameter and a shank portion for mounting the bit in a hand-held electric drill. The cutting section of the bit comprises a plurality of cutting edges disposed symetrically about the axis of rotation of the bit and extending rearwardly from the apex at an angle to the axis. The cutting edges have cutting portions and noncutting portions which are so-arranged that the cutting portions of one cutting edge cut selected diameters of a hole to be bored and cutting portions of another cutting edge cut other diameters of the hole whereby all cutting edges together cut all diameters of the hole. The sum of the lengths of the cutting portions of all of the cutting edges is approximately equal to the total length of one cutting edge so that the torque required to turn the bit is reduced.

Abstract: A motor comprises a rotor supported to rotate freely about its longitudinal axis while the axis is confined to an elastically bowed configuration by internal or external means. Heat, cold or other stress inducing means applied to the side of the rotor causes local internal stresses that cause the rotor to rotate in the direction that allows relaxation of the induced stress.