| 摘要 |
A holder (1) has a taper-shaped fitting section (4B) formed in a mounting hole (4), and a front end surface (2B) is set perpendicular to a centerline (O). A cutting head (10) has a taper-shaped mounting section (12) protruding from a rear end surface (11C) perpendicular to the centerline (O) of a cutting blade section (11). The cutting head (10) and the holder (1) are mounted to each other in such a manner that female and male threaded sections (3E, 13) are engaged with each other to thereby fit the mounting section (12) and the fitting section (4B) to each other and to thereby make the front end surface (2B) and the rear end surface (11C) in contact with each other. The inner/outer diameter ratio (d/D1) before the fitting, the inner/outer diameter ratio (d/D1) being the ratio between the inner diameter (d) of the fitting section (4B) and the outer diameter (D1) of the front end of the holder (1), is set to be in the range from 0.5 to 0.8, and the outer diameter expansion ratio ((D2 - D1)/D1 × 100 (%)) of the difference (D2-D1) between the outer diameter (D2) of the front end of the holder (1) after the fitting and the outer diameter (D1) to the outer diameter (D1) is set to be in the range from 0.022 × d/D1 - 0.003 (%) to 0.33 × d/D1 - 0.06 (%). |
