Abstract: A burnishing drill includes a cylindrical drill body connected at its forward end integrally with a shank. The forward end of the drill body includes a first pair of cutting edges inclined radially and rearwardly from the forwardmost central end of the drill body toward the shank at a first cutting angle. A second pair of cutting edges formed of diamond chips are disposed in a plane intersecting the plane in which the first pair of cutting edges are located. The second pair of cutting edges are inclined radially and rearwardly from a position inside a circle including the maximum external margins of the first pair of cutting edges toward the shank at a second cutting angle.

Abstract: A burnishing drill having a drill body, the forward end of which is formed with a reduced-diameter portion having its external diameter smaller than the maximum external diameter of the drill body. The forward end of the drill body includes a pair of first cutting edges formed in the reduced-diameter to include with a first cutting angle, and a pair of second cutting edges formed to extend radially in a direction perpendicular to the first cutting edges at least from the inward position of a plane including the outermost peripheral walls of the first cutting edges to the position of another plane including the outermost peripheral wall of the drill body.Each of the first cutting edges extends radially outward from the center of the forward end of the dril body and includes axially in the rearward direction while each of the second cutting edges inclines extends radially outward from the drill body and inclines axially in the forward direction.