Abstract
Straight or circular cutting edges at the chisel edge portion of conventional twist drills are formed usingelectrical discharge machining. Various shapes of main cutting edge changing into a concave or edge from a straight one are obtained by grinding the flank surface of the conventional twist drill for different pointangles. Cutting edge configurations of these drills are analyzed geometrically, and expresslons for inclination angleand normal rake angle along the cutting edge are derived. From the geometrical analysis, it is found that theinclination angle at the chisel edge portion takes positive or negative values with the location of straight or circularcutting edges and the normal rake angle along the main cutting edge of the drill having a32°helix angle varies onlyabout 20° by changing the point angle largely from 90° to 150°The torque and thrust force of these drills aremeasured using a piezo-electric type dynamometer, and the relations between chip form and cutting forces are discussed.
