| 摘要 |
PROBLEM TO BE SOLVED: To provide a drill which is free from any degradation of the rigidity compared with a drill of two types of a cutting blade and a chip discharging groove even when the diameter of the drill is small, free from any degradation of the chip dischargeability compared with a drill of one type of the cutting blade and the chip discharging groove, sufficient in hole position accuracy by simple improvement, and very excellent in practicability. SOLUTION: In the drill, a chisel edge 6 is provided on a tip, a spiral first chip discharging groove 1 and a spiral second chip discharging groove 2 are provided, land parts 3, 4 are provided between the first chip discharging groove 1 and the second chip discharging groove 2, and a cutting blade 5 is provided on an edge of a rake face 7 of the first chip discharging groove 1. The first chip discharging groove 1 and the second chip discharging groove 2 are provided in a non-point symmetric position with respect to a drill rotational center O, and a land part 3 behind the first chip discharging groove 1 is set to be larger than a land part 4 behind the second chip discharging groove 2. COPYRIGHT: (C)2006,JPO&NCIPI |
