| 摘要 |
Method of boring a pilot hole by inserting a boring tool (21) into a pilot hole formed on a workpiece beforehand to cut an inner wall face of the pilot hole, thereby forming a bored hole, wherein the boring tool (21) is provided with a shank part (22) rotated around an axis (O) and an edge part (23) arranged at the tip of the shank part (22), a chip discharging groove (27) extending from the tip side to the rear end side is formed at the edge part (23), a cutting edge (30) is formed at a crossed ridge part between the wall face of the chip discharging groove facing forward in the tool rotating direction and the outer peripheral face of the edge part, and a length (C) of the cutting edge (30) in the axis direction is made shorter than a length (H) of the pilot hole. |
