| 摘要 |
An object of the present invention is to provide a drill bit capable of easily drilling a drill hole that has no rifling, and has high circularity, can be easily positioned, the drill bit comprising a cutting blade tip which is composed of a block body of cemented carbide, three cutting blade portions are formed circumferentially equidistantly around the cutting blade tip, a connection line between a cutting surface 5 and a flank surface 6, said cutting and flank surfaces being formed in each said cutting blade portion 4a, 4b, 4c, acts as a main cutting edge 8 whereas a connection line between a connection surface 7 and said flank surface 6 acts as an auxiliary cutting edge 9, said main cutting edges 8 and said auxiliary cutting edges 9 cross at a blade tip point 10 so that said blade tip point 10 is shaped like a peak with no chisel edge, each said auxiliary cutting edge 9 lies on a line extending from said main cutting edge 8 of a said cutting blade portion located opposite across said blade tip point 10, and each of said main cutting edge 8, said auxiliary cutting edge 9, and a connection line between said connection and cutting surfaces 7, 5 crossing at said blade tip point 10 extends in a straight line. <IMAGE> |
