| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To provide a drill body which is so rigid that its surrounding partial edges forming a negative angle enables the drill body to have the best and longest operational lifetime. <P>SOLUTION: The drill body has a front head (4) formed in a front-end part provided with two cutting edges. A first partial edge is included in a central head-end part (8) having a front chisel edge (29). A second partial edge extends between a circumference end point (11) and an inside end point (12) in a radial direction in which the second partial edge shifts to the first partial edge (9). Two partial surfaces (13a, 13b) of a first gap surface (13) are joined to each other in a chute bottom (17). The drill body includes a second chute bottom (30) which extends in an extended part of the first chute bottom (17) and separates two second partial surfaces (15a, 15b) which are included in a second gap surface (15). <P>COPYRIGHT: (C)2010,JPO&INPIT</p> |
