| 摘要 |
PROBLEM TO BE SOLVED: To provide a highly practical drilling tool capable of greatly improving breaking resistance and hole position accuracy compared with a conventional PCB drill.SOLUTION: A drilling tool is configured so that, at the outer periphery of a tool body 1, a first chip exhaust groove 2a including three twist regions having predetermined twist angles and a second chip exhaust groove 2b including two twist regions having predetermined twist angles are arranged, and in the midway part of one chip exhaust groove, the other is continuously disposed, and two grooves, a parallel running transfer part, and a parallel traveling part are sequentially arranged from the tip side. The twist angles of the parallel traveling parts of both chip exhaust grooves are set larger than those of the two grooves, and the changing position of the twist angle located at the most tool tip side is set at a position of 1/2 or smaller than the groove length of the chip exhaust groove formed from the tool tip to a predetermined position of the base end side of the tool body 1 larger by 1.5 times or more than a tool diameter. |
