| 摘要 |
This drill has a plurality of convex-arc-shaped cutting blades (4a, 4b) formed on the distal-end side of a drill body, the cutting blades extending from the outer periphery of the drill body to a chisel edge (14) near the axis of rotation, wherein the drill further has: substantially strip-shaped second surfaces (5a, 5b) formed along the convex-arc-shaped cutting blades, the second surfaces being formed rearward along the rotation direction from the convex-arc-shaped cutting blades; third surfaces (6a, 6b) formed sequentially rearward along the rotation direction from the second surfaces; and fourth surfaces (7a, 7b) formed sequentially rearward along the rotation direction from the third surfaces. |
