Cutting Behavior of Drill Point at Beginning of Drilling

Abstract

In the drilling process using twist drill, point shape of drill is closely related with machining characteristics. Especially, it is generally known that chisel edge angle has an influence on machining characteristics such as machining accuracy. The cause of the roundness error of machined hole is wandering of drill. There were many studies about wandering motion of drill, and most of these studies analyzed mechanism of wandering by detecting the motion of drill point. However, there were few research works on the relation between wandering and shape of drill point. Therefore, wandering behavior was examined with different angle of chisel edge, and moreover the mechanism of start of wandering and change of wandering motion were observed. Results obtained are as follows : (1) Wandering starts when major cutting edge starts to cut. (2) The larger the chisel edge angle is, the larger the wandering motion is. (3) In the case that chisel edge angle is less than 115deg. wandering becomes small and circular motion. (4) With increase of the chisel edge angle from 115deg. to 137deg. wandering changes from polygonal to triangular.