US Patent 7364390 Drilling tool

Disclosed is a drilling tool comprising a first drill bit (2) that is provided with at least two forward cutting edges (4, 5) and a second drill bit (3) which encompasses at least two rear cutting edges (6, 7). A cutting groove (8, 9) runs continuously from one respective forward cutting edge (4, 5) to a rear cutting edge (6, 7). Said cutting groove (8, 9) is embodied in an asymmetric manner in an area (A) bordering the forward drill bit (2), in a symmetric manner in a central area (B), and asymmetric in an area (C) bordering the rear drill bit (3).