| 摘要 |
PROBLEM TO BE SOLVED: To provide a drill capable of drilling with higher degree of accuracy compared with a conventional drill. SOLUTION: In a peripheral surface 13 of a blade part which is the tip side part of a drill body 10 rotated around an axis CL, two main grooves 20, 30 are extended from a pair of tip flanks 12a, 12b formed on a tip surface 12 of the blade part toward a base end side. The drill includes: a first cutting edge 21 formed on a cross ridgeline between a wall surface 22 facing the forward side in the drill rotational direction K of one main groove in the two main grooves and the tip flank 12a, and extended to the peripheral end of the drill body; and a second cutting edge 31 formed in an inner circumference side area of a cross ridgeline between a wall surface 32 facing the forward side in the drill rotational direction K of the other main groove having a shorter groove length compared with the one main groove 20 and the tip flank 12b of the blade part except a non-cutting part 41 formed by a minor groove 40 notching a peripheral part of the cross ridgeline and the wall surface 32 connected to the peripheral part to a rear side in a drill rotational direction K. COPYRIGHT: (C)2010,JPO&INPIT |
