New type drill with three major cutting edges

Abstract

Drilling performance of a new type twist drill is described. The new type drill has three major cutting edges, three chisel edges and three flutes. This drill is an efficient means of making a hole with high accuracy and no reaming. Recently, some research on drill materials including surface coating, drill point geometry, cutting forces and tool life have been carried out in order to increase the cutting performance of drills. All the drills used in these experiments were ordinary drills with two major cutting edges. The authors calculated the point geometry of the new type drill, and also examined the cutting characteristics of the drill with respect to cutting forces, hole accuracy and tool vibration. The experimental results showed that the whirling vibration which frequently occurs in an ordinary drill with two major cutting edges disappears when the new type drill is used, and thereby rifling marks do not result on the hole surface. Consequently, a hole with high roundness and straightness is obtained.