A drill bit comprising a tool holder (1) having a tip end having two cutting inserts (5, 5') on a main plane (C-C), the cutting inserts (5, 5) ') has a short central cutting edge oriented on a common second plane (E-E). The cutting edge forms a point-like central cutting edge for entering the workpiece and thereby centering the drill bit. On the arbor, two chip flutes (6, 6') are provided, which extend from the tip end to the bottom end. In any section along the arbor, the flutes are located diametrically opposite each other in the plane of the tube, and the plane of the tube is in the plane of the common land (F-F) of the two lands on both sides of the tube. Extending at 90°, the arbor has maximum rigidity in this plane. The second plane (E-E) of the central cutting edge is oriented at an angle of approximately 90 to the major rigid direction (F-F) of the land plane or the bottom end of the shank.
In a drilling operation for concrete or the like, it is possible to alleviate the sudden change of the drilling state, and to stabilize the drilling operation, even when generating large-sized chips, the drilling efficiency is not lowered.
A cutting edge portion arranged substantially in a radial shape, having at least two main cutting edge portions, and at least two auxiliary cutting edges disposed between the main cutting edge portion and the main cutting edge portion in the circumferential direction The main cutting edge portion has a main cutting edge as a cutting edge thereof, and the inner end of the main cutting edge is located at the center of rotation, and the outer end is located at the outer edge of the rotation locus of the cutting edge portion.