| 摘要 |
PROBLEM TO BE SOLVED: To provide a twist drill for forming a stepped hole, which is for use in grinding a hard fragile material to form the stepped hole therein, and can form the inner surface of the stepped hole as a smooth surface with high accuracy. SOLUTION: A diamond twist drill 1 has a diamond grindstone 2 attached to the tip of a shank 3, and an axial penetration hole 6 formed at the diamond grindstone 2 for feeding a fluid therethrough. The diamond grindstone 2 has a side surface grindstone 2a, a front surface grindstone 2b, and a protruded grindstone 4 protruded from the tip of the front surface grindstone 2b. When a through hole 10 having an annular step 10a is formed at a hard fragile material 9 by using the diamond twist drill 1, the dimension of the hard fragile material 9 and a dimension concerning the shape of the diamond twist drill 1 are specified so that the hard fragile material 9 is ground by the front grindstone 2a to form the annular step 10a with a predetermined residual thickness D left at the bottom of the hard fragile material 9. COPYRIGHT: (C)2006,JPO&NCIPI
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