| 摘要 |
PROBLEM TO BE SOLVED: To provide a drill and a drilling method of stacked plates excellent in processing accuracy, capable of being applied to drilling processing of the stacked plates or thick material, reducing the number of processing steps until achieving a required hole diameter, and extending a tool life.SOLUTION: At a tip of a body 10, there is provided a pilot shaft part 20 having a diameter smaller than that of the body 10, and protruding concentrically with the body. The pilot shaft part 20 includes: a shaft main body part 21; a tip flat surface 22 located at a tip of the shaft main body part 21; and a tip taper surface 23 located between an outer peripheral surface of the shaft main body part 21 and the tip flat surface 22, and having a predetermined point angle &bgr;. The body 10 includes: an odd number of helical flutes 11 provided on an outer peripheral surface; and three cutting blades 13 on a body tip surface 12 having a predetermined point angle α, provided at an area from the outer peripheral surface to the pilot shaft part 20. The pilot shaft part 20 includes: auxiliary helical flutes 24 connected to the helical flutes 11, and provided from the outer peripheral surface of the shaft main body part 21 to the tip taper surface 23; and auxiliary cutting blades 26 provided on the tip taper surface 23. |
