| 摘要 |
A hammer drill bit has an axis, a shaft and a crown and a plurality of hard metal circumferential studs carried by the crown and distributed along a circumference thereof. Each circumferential stud has an axis inclined at an acute angle with respect to the bit axis and a conical cutting tip oriented obliquely away from the bit axis. The acute angles of the axes of consecutively viewed circumferential studs alternate between a relatively large magnitude and a relatively small magnitude differing by 10 DEG to 25 DEG from one another. |
