| 摘要 |
A drill includes a cutting section having a cylindrical shape and configured to be rotated about a rotation axis. The cutting section includes a first cutting section and a second cutting section, at a front end portion thereof, a first flute continuous with the first cutting section and extending helically around the rotation axis toward a rear end of the cutting section, and a second flute continuous with the second cutting section and extending helically around the rotation axis toward the rear end of the cutting section. The first cutting section includes a first inner cutting edge and a first outer cutting edge positioned closer to the outer peripheral surface than the first inner cutting edge and gradually inclined to the rear end of the cutting section toward the outer peripheral surface. The first inner cutting edge is positioned closer to the rear end of the cutting section than the inner end of the first outer cutting edge. |
