| 摘要 |
A drill according to the present embodiment has a long shape including a rotation shaft, and includes: a hole boring portion located at a first end side; a shank portion located at a second end side; and a tapered portion which is located between the hole boring portion and the shank portion and the diameter of which is larger at the second end side than at the first end side. The hole boring portion includes a first helical groove and a first cutting blade located at the first end side of the first helical groove. The tapered portion includes a second helical groove connected to the first helical groove, a second cutting blade located at the first end side of the second helical groove, and a chamfered portion located along the second cutting blade. In the tapered portion, a connection portion between the second cutting blade and the hole boring portion is a curved surface, and the chamfered portion becomes gradually smaller in size toward the first end side. When the length of the second cutting blade in a front view of the first end is L and the width of the outer circumferential end of the chamfered portion in a direction parallel to the rotation shaft is w, w/L is 0.0015-0.5. |
