| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a drill capable of stably and accurately drilling a workpiece formed by laminating a metal member and a fiber-reinforced resin composite material over a long term when drilling the workpiece at once. <P>SOLUTION: This drill is a stepped drill (a) having two or more steps by axially dividing a cutting blade, wherein the cutting blade 10 at the first step from the tip is formed into a characteristic small in cutting thrust resistance as compared with the case where it is formed to have the same number of cutting blades, the same tip angle and the same relief angle as the cutting blades after the second step by being formed to have a small number of cutting blades, a large tip angle or a large relief angle relative to the cutting blades 20, 30 from the second step. For instance, the first step has two blades, the second step has four blades, the third step has four blade, the tip angles satisfy a condition of θ<SB POS="POST">1</SB>>θ<SB POS="POST">2</SB>>θ<SB POS="POST">3</SB>, the relief angles satisfy a condition of γ<SB POS="POST">1</SB>≥γ<SB POS="POST">2</SB>≥γ<SB POS="POST">3</SB>, each of the first and second steps has a constant tip angle, the third step is formed into a curvilinear shape where a blade edge ridge line is smooth by gradually reducing the tip angle as moving to the drill rear end side. <P>COPYRIGHT: (C)2013,JPO&INPIT |
