| 摘要 |
PROBLEM TO BE SOLVED: To form a high-quality through-hole without any burrs in a work material of CFRP or the like in which the burrs are easily formed by machining by a drill, and to drastically improve the service life of the drill. SOLUTION: A drill body 3 is provided with a preceding work part 4 for drilling a preparatory hole in the work material and a finishing part 5 having a finishing blade 7 on the tip. A diameter difference between the outside diameterϕD2 of the finishing part 5 and the outside diameterϕD1 of the preceding work part 4 is adjusted to be above 0.1 mm and below 2.0 mm. A chip discharging groove 8 is formed as a high-helix groove having a torsion angleβof 40°or larger, and the surface of the drill body 3 is covered with a diamond coating. COPYRIGHT: (C)2008,JPO&INPIT
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