| 摘要 |
PURPOSE: To prevent sticking of a drill bit having a drill head, for making a drilled hole, at the time of drilling, by providing a scraping edge for removing drilled scraps generated at an enlarged diameter portion, a cylindrical step portion connected to the enlarged portion, and a transition portion to the step portion, during the drilling. CONSTITUTION: A drill bit 1 makes an undercut by the action of side cutting blades 7, 8 attached to a drill head 6. Next, an enlarged diameter portion is formed which is spaced a predetermined interval away from the drill head 6, and the enlarged diameter portion is laterally rotated while being in contact with a drilled hole wall. Further, a step portion 11 which is reduced in diameter is formed at a location connected thereto and closer to a depth stopper 2, and a scraping edge 12 is provided at a transition portion between the enlarged diameter portion and the step portion. By the scraping edge 12, drilled scraps are scraped from the drilled hole wall at the time of lifting and drawing the drill bit 1. In this manner, drilled scraps generated during the drilling are removed via a drilled scrap ditch 13, which enables operation of the drill bit 1 without sticking. |
