Abstract: A burnishing drill includes a cylindrical shank and a drill body connected to the shank. Drilling edges, first reaming edges and second reaming edges are formed on a first reduced diameter portion, a second reduced-diameter portion and a third reduced-diameter portion respectively located at a foremost end of the drill body. Each of the reaming edges is inclined with respect to the longitudinal axis of the drill at an angle which is set so as to be within a range of between 5.degree. and 30.degree.. During a boring operation using the drill, a hole is drilled by the drilling edges and the drilled hole is then worked by the first reaming edges and the second reaming edges to provide a smooth inner wall in the drilled hole. Since each of the reaming edges is formed to extend radially outward from the foremost end of the drill and incline axially in the rearward direction at a relatively small angle, the centering property can be greatly improved.

Abstract: A burnishing drill includes a cylindrical shank and a drill body connected to the shank. Drilling edges, reaming faces and reaming edges are formed on a first reduced-diameter portion, a second reduced-diameter portion and a third reduced-diameter portion located at a foremost end of the drill body respectively. The reaming faces which are located axially at backward positions of the drilling edges and the reaming edges extend radially outward from the foremost end of the drill and incline axially in the rearward direction, and also extend radially outward and incline in the rearward direction with respect of the rotational direction. Since an inner surface of the hole drilled and reamed by the drilling edges and the reaming edges can be further smoothed by the reaming faces, the surface roughness of the finished hole can be much improved.

Abstract: A high speed burnishing drill having drilling edges and reaming edges provided at the forward end of a cylindrical drilling body. The drilling edges are inclined diametrically from the center of the forward end to the axially rearward direction, while the outermost peripheral wall of the drilling edges are on a reduced-diameter portion of the maximum external diameter of the drill body. The reaming edges extend from the plane intersecting the drilling edges radially from a position inward of the outermost peripheral of the drilling edges, outwards, so as to incline axially in the forward direction with a second cutting angle. A reduced diameter portion extends axially backward from the outermost peripheral wall of the drilling edges. An enlarged-diameter guide face extends axially from a slope behind the corresponding drilling edge in the rotational direction, and the forwardmost end of the enlarged guide face is located axially behind the corresponding reaming edge.

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.