| 摘要 |
A drill comprising a holding section, a prismal section receivable by the holding section, and a top-truncated, pyramidal section which is integral with the prismal section, with the prismal section having side faces and side ridges defined by the adjoining two side faces, the top-truncated, pyramidal section having end faces which taper and coverage on the axis of rotation of the drill, end ridges which are defined by meeting of the adjoining two end faces, and a truncated surface extending across the axis of rotation and forming an angle of more than 1 DEG to less than 90 DEG with the cross-section of the prismal section. The end faces and end ridges of the pyramidal section extend from said side faces and side ridges of the prismal section, respectively. Because the apex of the drill is located out of the axis of rotation, it has enhanced cutting performance.
|
