DRILL

摘要

PURPOSE: A drill is provided to improve cutting performance using four edges including a main edge and a sub edge according to wear condition. CONSTITUTION: A drill comprises a pair of main edges(A) and sub edges(B). A pair of main edges are formed from the front end to the rear end(G) of a drill. A pair of sub edges are formed at the F-G parts of the maximum diameter(E). The front end(B1) of the sub edge is positioned within the angle narrower than 90°at the rear part from a front end of a main edge in a rotational direction. The front end angle of the sub edge is larger than the front end angle of the main edge.