| 摘要 |
PURPOSE:To prevent run-out of a drill at its biting and smoothly perform cutting work, by locating the start end of a lip about to the rotating center, while protruding said start end to the topmost end, and forming a rotating locus of the lip about to a conical shape with the start end of the lip as the vertex. CONSTITUTION:Center lip parts 31, 31', protrusively curved for the direction of rotation of a drill, are provided in the vicinity of the rotating center of a drill 10, and a lip start end 0 of the lip part is arranged about to the center of rotation. A rotating locus of lips 30, 30' is constituted almost to a conical shape formed with the lip start end 0, about in the center of rotation, as the vertex, at a start of drilling a hole, the lip start end 0 about in the center of rotation always starts biting first, and generation of run out can be prevented to increase a life of the drill. |
