Investigation in Tool Life of Twist Drills

It is well known that geometrical parameters of the drill point, i.e., relief angles, chisel form and web size, have a major influence on the drill's performance. This paper deals with the influence on the drill life of some geometrical errors which were often completely neglected in drilling tests. Two different drill groups of different manufactures were tested. The results show that regular production scatter of each of the geometrical errors may influence the drill life by 30 percent. However, some combinations of errors may also double or even triple the above. Some ideas of drill testing procedures are discussed.