| 摘要 |
[Problem] To provide a drill and a method for drilling a layered plate which can be applied to drill machining of a layered plate or a thick material, which can have fewer machining steps to reach the desired hole diameter, and which has a longer tool service life and exceptional machining precision. [Solution] In the tip of a body (20) is a pilot shaft part (30) protruding concentrically, the pilot shaft part (30) having a smaller diameter than the body (20). The pilot shaft part (30) is provided with a shaft major body part (31), a tip flat surface (32) positioned at the tip of the shaft major body part (31), and a tip tapered surface (23) having a prescribed tip angle ß, the tip tapered surface (23) being positioned between the outer peripheral surface of the shaft major body part (31) and the tip flat surface (32). The body (20) is provided with an odd number of helical grooves (22) in the outer peripheral surface thereof, and three major cutting edges (23) in a tip tapered surface (25) formed at a prescribed tip angle a in an area extending from the outer peripheral surface to the pilot shaft part (30). Formed in the pilot shaft part (30) are auxiliary helical grooves (24) joined to the helical grooves (22) from the outer peripheral surface of the shaft major body part (31) to a tip tapered surface (33), and auxiliary cutting edges (34) in the tip tapered surface (33). |
