A drill bit includes a shank (1) having a tip with two cutting inserts (5, 5') located on a main plane (C-C), the cutting inserts (5, 5') having short central cutting edges 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.  Two junk slots (6, 6') are arranged on the cutter bar, and the junk slots (6, 6') extend from the tip end to the bottom end.  In any cross section along the cutter bar, the junk slots are located at radially opposite positions to each other on the pipe plane, which extends at 90.d egree. to the common blade plane (F-F) of the two blades on both sides of the pipe, and the cutter bar has the greatest rigidity in this plane.  The second plane (e-e) of the central cutting edge is oriented at an angle of approximately 90.d egree. to the main stiffness direction (f-f) of the blade plane or the bottom end of the shank.

The invention relates to a drill bit which can alleviate the sudden change of the drilling state in the drilling operation on concrete and the like, stabilize the drilling operation, and prevent the drilling efficiency from being reduced even when large particles of chips are generated.

A cutting edge part which is arranged in a substantially radial shape has at least two main cutting edge parts and at least two auxiliary cutting edge parts which are arranged between the main cutting edge part and the main cutting edge part in the circumferential direction, wherein the main cutting edge part is provided with a main cutting edge serving as a cutting edge thereof, the inner end of the main cutting edge is positioned at the rotation center, and the outer end is positioned at the outer edge of the rotation track of the cutting edge part.

The secondary cutting edge portion has a secondary cutting edge as its cutting edge, the inner end of the secondary cutting edge is located at a position deviated from the rotation center toward the outer diameter side, and the outer end is located at a position deviated from the outer edge of the rotation track of the cutting edge portion toward the rotation center side.

A drill bit is provided with a plurality of cutting edge parts arranged at the front end of the drill bit, and a shaft-shaped drill bit main body which is arranged on one side of the base end of the cutting edge part and has a handle part formed on the base end;

The cutting edge portion has a cutting edge formed by projecting the joint edge of the cutting surface and the back clearance surface toward the front end side, and the cutting edge is arranged in a substantially radial shape from the rotation center side to the outer diameter side of the drill bit;

Which performs impact cutting by a combined action of a rotating action and an action in the axial direction, is characterized in that the cutting edge part has at least two main cutting edge parts and at least two auxiliary cutting edge parts which are arranged between the main cutting edge part and the main cutting edge part in the circumferential direction;

The main cutting edge portion has a main cutting edge as its cutting edge, the inner end of the main cutting edge is located at the rotation center, the outer end is located at the outer edge of the rotation track of the cutting edge portion, the sub cutting edge portion has a sub cutting edge as its cutting edge, the inner end of the sub cutting edge is located at a position deviated from the rotation center to the outer diameter side, and the outer end is located at a position deviated from the outer edge of the rotation track of the cutting edge portion to the rotation center side.