| 摘要 |
Drill bit of the twist drill type with turns which are held together by a drill centre web and each issue in a radially extending cutting edge of which one extends to the bit axis and the other is shorter than it. This is characterised by the following features: a) the cutting edges (2,3) formed by continuos straight edges lie essentially in a plane coinciding with the bit axis (9), b) the cutting edges (2,3) form an obtuse angle (cutting angle), lying below 180 DEG , of at least 175 DEG , c) the cutting edges (2,3;16) having a leading edge angle (K) of about 30 DEG with a rake angle (S1, S15) of about 30 DEG to 45 DEG , d) the diameter (D) of the drill centre web (6) is at most half the bit diameter. <IMAGE> |
