| 摘要 |
<p>A drill bit in which drilling performance does not deteriorate and the outside-diameter end of the edge does not fracture. The drill bit A is provided with a plurality of cutting edge portions (1) in the circumferential direction where the joint ridge (4) of the cutting face (2) and the flank (3) formed in each cutting edge portion (1) forms a cutting edge, and the inner-diameter ends of respective cutting edges are joined at the central part of the bit tip to form a tip portion (10). At least one cutting edge portion (1) has a first flank (3A) at the circumferential end and a second flank (3B) on the inner circumferential side thereof, wherein the first flank (3A) has a cutting edge side flank (3a) close to the cutting edge and a proximal end side flank (3b) formed on the proximal end side of the cutting edge side flank, and the inclination angle a1 to the axial direction of the cutting edge side flank (3a) is set smaller than the inclination angle a2 to the axial direction of the proximal end side flank (3b).</p> |
