| 摘要 |
TASK An inexpensive drill with high processing accuracy is provided. MEANS FOR SOLVING THE PROBLEM A chisel edge 11 of a tip 12 is removed, and a pyramid 1 is formed in that part, in which an inclination angle theta1 of each edge 4 extending from an apex P relative to a center line of the drill CL is formed to be larger than an angle theta2 that is one-half of a drill tip angle theta0, and so chisel steps are resolved and stable cutting becomes possible, thereby improving hole accuracy. Also, it is possible to form the pyramid 1 by grinding a tip of an existing drill by a grinder, so that a drill can be realized at a low cost. |
