| 摘要 |
PROBLEM TO BE SOLVED: To provide a drill with a plurality of cutting edges which has an improved thinning shape of a rotation center part to suppress abrasion at a position where the groove surface of the thinning part meets the groove surface of a flute groove, and improves discharge of scraps in the thinning part to improve processing performance and life thereof.SOLUTION: A thinning part 4 employs two-stage thinning with a first thinning part 4disposed on the rotation center side and a second thinning part 4connected to the first thinning part at an angle. The axial rake angle of the first thinning part 4is set within the range from -5° to -10°, and the axial rake angle of the second thinning part 4relative to the axial rake angle of the first thinning part is set within the range from +2° to +4°. |
