| 摘要 |
PROBLEM TO BE SOLVED: To include a form protecting a drill from damage by overheat when a cooling material is missing. SOLUTION: It is provided with a chunck 110 for driving a drill 100, a body 120 connected to the chunck 110 and including a surface, a groove 130 provided on the surface, a cutting blade 160 provided on the tip of the drill 100, and an outer circumference run off surface crossing the outer circumference at the outer circumferential point of the groove edge with regard to the cross section of the drill 100 perpendicular to the drill 100 axis and extending outward from the surface of the body 120 to the outer circumference of the drill 100. This drill 100 includes an improved performance resisting the missing of a cooling material during drilling without critically overheating the drill 100 or the drilled piece and hardly damaging the drill 100 and the drilled piece. |
