| 摘要 |
PURPOSE: To provide a twist drill-type drill bit comprising the spiral parts integrated by a drill center web, and capable of providing the superior cutting free from chips. CONSTITUTION: Each spiral part of a twist drill type drill bit reaches a radially extended cutting edge, one of edges is extended to a bit axis and the other edge is shorter than it. In this drill bit, the cutting edges 2, 3 formed by the continuous straight edges lie essentially in a plane coinciding with the bit axis 9, an obtuse angle of the cutting edges 2, 3 is above 175 deg. and below 180 deg., the cutting edges 2, 3 have about 30 deg. to 45 deg. of a rake angle (S1 ) and about 30 deg. of a leading edge angle (K), and a diameter D of the drill center web 6 is at most half the bit diameter. |
