| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To obtain a hard material head for a percussion-rotary drill further optimized for the purpose of increasing durability in cutting obliquely relative to a reinforcement material. <P>SOLUTION: A percussion-rotary drill includes a hard material head 3 having two major cutting bits 4 each having a main cutting edge 5, and two minor cutting bits 6 each having a minor cutting edge 7 axially offset rearwardly along a rotational axis A of the drilling head relative to an adjacent major cutting edge 5, with the two minor cutting bits 6 each having, in its radially outer region on both sides of the minor cutting edge 7, a tangential edge 8 extending at an angle thereto. Suitably, the tangential edge 8 and the minor cutting edge 7 adjacent to this tangential edge 8 are made to form an edge angleαin the range of 50-85°. More suitably, the major cutting bits 4 are provided in a radial direction and extended over the entire range of a drill diameter B. <P>COPYRIGHT: (C)2009,JPO&INPIT</p> |
