Zylinderkopfbohrer

摘要

The drill's (1) main blade (4) with centring point (5) has free-cut surfaces (11) and extends over the entire circular cross-section of the drill-head (3). Slanting drilling-dust ducts (7) penetrate the drill head and are open towards the edge next to the main blade. Each end of the main blade adjoins a pre-cutting edge (8) coinciding with the peripheral line of the drill-head. The pre-cutting edge extends as far as the edge of the outer drilling-duct, and is formed by the edge of a cylindrical outer wall (6) of the drilling head. The otherwise smooth outer casing wall is broken up by radial outward bulges (13) interspersed by grooves (12) sloping towards the axis or parallel with the axis.