| 摘要 |
<P>PROBLEM TO BE SOLVED: To improve accuracy of an inlet hole diameter and an exit hole diameter, to exhibit stable performance and to suppress occurrence of burrs at the hole exit in a throw-away drill having cutting edges constructed from a plurality of throw-away tips. <P>SOLUTION: Throw-away tips 5<SB>-1</SB>, 5<SB>-2</SB>constituting a center edge 8 and an outer circumference edge 9 are mounted on a tip end of a drill body 1. Proportions between the cutting amount A of the center edge 8 and the cutting amount B of the circumferential edge 9 are set such that the center edge 8 has a greater proportion, and the throw-away tip 5<SB>-2</SB>is projected axially forward from the throw-away tip 5<SB>-1</SB>so that biting in to a workpiece starts at an outer end corner 9a of the outer circumferential edge 9. <P>COPYRIGHT: (C)2008,JPO&INPIT |
