A new approach to eliminate twist drill chisel edge Part 2. Symmetric configuration
提出了两种新型钻头构型，一种通过直径向唇消除横刃，另一种结合直唇与曲线唇以延长钻头寿命。
The flute shape to produce two new drill configurations are presented. The first configuration is to provide a straight diametral lip which could be extended to eliminate the chisel edge. The second configuration, which encompasses the feature of the first one at the inner portion of the lip and the curved shape at the outer portion of the drill lip, is provided to enhance the overall life of the drill.