| 摘要 |
PROBLEM TO BE SOLVED: To provide a drill which has at least three cutting edges arranged in nearly the same radial direction in a cutting head portion, and has chip ejecting flutes formed on its outside surface, and can achieve high machining precision even in machining a hole having a large ratio of a drilling depth to a hole diameter. SOLUTION: An inside cutting edge portion 2C is arranged at the back of an outside cutting edge portion 2A and a middle cutting edge portion 2B in the drilling direction. A guide pad 3A to be brought into sliding contact with the inside peripheral surface of the drilling hole is fixed to at least the position on the outside peripheral surface of the cutting head portion 1a, to which position the cutting reaction force by the inside cutting edge portion 2C is applied. The guide pad 3A is positioned such that its front end portion is fitted in an annular groove G cut by the outside cutting edge portion 2A before the start of the cutting by the inside cutting edge portion 2C. COPYRIGHT: (C)2007,JPO&INPIT
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