| 摘要 |
PROBLEM TO BE SOLVED: To provide a drill bit capable of punching an undercut-type prepared hole continuously formed with straight hole parts having smaller diameters than that of a prepared hole general part on a hole bottom side of a tapered hole part, before construction of a post-construction anchor. SOLUTION: A cutter blade 183 for punching the straight hole part 22 and a cutter blade 184 for punching the prepared hole general part 20 are provided at a distal end of a cutter body 182. The cutter blade 183 first punches the straight hole part 22, and the cutter blade 184 in no diameter expanded state punches the prepared hole general part 20 to expand the diameter of the straight hole part 22. At a stage when the prepared hole depth becomes a prescribed depth, the cutter blade 184 is expanded in diameter with oscillation and projection of the cutter blade 184, thereby machining a part adjacent to the straight hole part 22 into the tapered hole part 21. COPYRIGHT: (C)2008,JPO&INPIT
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