| 摘要 |
A drill according to an embodiment of the present invention has: a pair of main cutting edges which are located at the front end of the drill body; a pair of first chisel edges which extend respectively from the pair of main cutting edges toward the rotation axis; and second chisel edges which are located between the pair of first chisel edges and which intersect the rotation axis of the drill body. In a cross-section of the rotational paths of the first and second chisel edges, taken so as to include the rotation axis, the respective rotational paths of the pair of first chisel edges have a rectilinear shape, and imaginary straight lines which are extended respectively from the rotational paths of the pair of first chisel edges toward the rotation axis are located closer to the rear end of the drill body than the rotational paths of the second chisel edges. |
