| 摘要 |
A drilling head has a cylindrical body with a longitudinal axis, tapering towards a leading end thereof. The drilling head comprises at least two chip evacuation flutes and at least two lands therebetween. Each flute has a first side all facing in the direction of rotation of the drilling head and a second side wall diverging outwardly from the first side wall and merging therewith via a web-thinning recessed surface extending towards this leading end. Each land is bound by the first wall of one adjacent flute and the second wall of another adjacent flute and has a generally radially extending and axially inclined front flank face tapering towards the leading end. The front flank face of each land intersects the first wall of one flute at a primary cutting edge, the web-thinning recessed surface of this flute at a secondary cutting edge, and the front flank face of the other land at a chisel edge which is disposed at the leading end of the drilling head and which passes through the longitudinal axis thereof. The chisel edge is concave and merges with the secondary cutting edges of the two lands via axially outermost extremities thereof which are spaced from the longitudinal axis. |
