The invention relates to a drill bit which extends along a center axis in the axial direction, comprising main cutting edges, which are connected to one another by a transverse cutting edge, comprising a tool flank adjoining each of the main cutting edges, which tool flank respectively merges into a chip flute, comprising an additional point thinning in the region of the transverse cutting edge, and comprising a drill back configured peripherally between the chip flutes.
A drill bit of this type can be derived, for instance, from WO 2011/151155 A1.
In drilling tools, the problem generally exists that in the center only an inadequate chip evacuation takes place, which, inter alia, leads also to higher cutting forces. This problem arises in the region of the transverse cutting edge. In order to reduce this problem, the so-called point thinning is known, by which, in the region of the transverse cutting edge, additional material is removed, so that an improved chip evacuation, in particular also in the region of the center, is obtained. The point thinning is usually made by an additional grinding operation, in that a grinding wheel is attached in the region of the transverse cutting edge to the end face of the drill bit.
Similarly, in a so-called four-face starting cut, in addition to the tool flank adjoining the respective main cutting edge, a further face with stronger inclination than the tool flank is ground. However, as a result of these additional grinding operations, edges, which are disturbing, are usually formed, in particular in the transition to the chip flute.
A drill bit in which, by a special grinding process, the tool flank merges homogeneously and without edges into the chip flute is described in EP 1 230 058 B1. By virtue of the special grinding process, the tool flank here descends steeply in the transition to the chip flute. An additional point thinning is in this case explicitly dispensed with. The special grinding process therefore replaces the otherwise customary point thinning, which is usually made by a second grinding step.