Modification of Drill Point for Reducing Thrust

A considerable amount of thrust force during drilling is due to the cutting action at the chisel edge of drills. This is in turn due to large values of negative rake angle along with a very small cutting velocity in the zone of chisel edge. The authors have developed a grinding technique for modifying the chisel edge into a pair of auxiliary cutting edges with positive rake angle by generating two slots at the chisel point in a manner similar to Zhirov-point drills. Analytical expressions have been developed for analyzing the geometry of modified chisel edge. Experimental investigations have indicated that during drilling of cast iron such modifications result in the reduction of thrust force by about 50 percent. However, there is an optimum orientation angle and setting angle which should be chosen during grinding of drills in order to get the maximum benefit in regards to the reduction of thrust force.