Effects of point geometries of twist drills on drilling

The twist drill is one of the most widely used yet complex of all cutting tools. There are many factors which influence drill performance including both the drill and drill workpiece materials. Another major affecting the performance of the drill is the drill point shape. The drill point is the most critical part of the drill and small variotions in its geometry can have a strong influence on its performance. In this paper different types of drill point geometries were investigated. The invastigations results showed that the whirling vibration which frequently occurs in an ordinary drill with two major cutting edges disapears when the three cutting edges drill used, also a hole with high roudness and straightness is obtained. The cermented carbide drill with three cutting edges is more effective than a conventional drill with two cutting edges, expect for cylindiricity. Split point drills have found extensive and successful use in industry due to their ability to reduce the trust and to provide a positive rake cutting edge and a chip breaking point. The advantages of the desing of Multifacet Drills (MFD) over conventional twist drills are lower cutting forces, improved heat transfer, impoved chip ejection, improved hole quality and higher productivity or longer toll life. The drill thrust developed by the New Point Drill (NPD) was singficantly lower in comprasion to that of the other carbide tipped drills. The invastigations showed that, the advantages of the double cone drill which has 60° second cone angle over conventional twist drill are, improved drilling performance and more drill life. Despite these facts, twist drills of the traditional geometry used almost one hundred years ago are still in use very widely. The main reason for this seems to be the fact that all of these new geometries are complicated and require sophisticated instruments for grinding. xv