Patent ID: 7762748
Filing Date: 2010-07-27
Classification: B23B,Y10T

Abstract:
1. A drill comprising: a chip discharge groove that extends towards a proximal side of the drill body is formed at the periphery of a cutting tip provided on a distal side of the drill body that rotates around an axis; a cutting edge formed at an intersection ridgeline portion between a wall face of the chip discharge groove that is directed forward in a drill rotation direction, and a distal flank face of the cutting tip; a thinned portion having: a plurality of cutting oil feed holes that extend from the proximal side towards the distal side are provided in the drill body so as to be located on a reference line that extends towards a circumferential central portion of an outer circumferential surface of the drill body split by the chip discharge groove from the axis in a cross section orthogonal to the axis, wherein a cutting oil feed hole that is located on the radial outermost side is used as a first cutting oil feed hole, and a cutting oil feed hole that is on the radial innermost side is used as a second cutting oil feed hole, wherein two or more openings of the cutting oil feed holes are provided for the cutting edge whereby the plurality of cutting oil feed holes are formed with centers radially displaced from and in the vicinity of an intersection ridgeline portion between the distal flank face and the second thinned face, and wherein a ratio F/R of an angle F that is formed between the reference line, and a straight line that passes through the axis and a front end of an outer circumferential surface of the drill body in the drill rotation direction that is split by the chip discharge groove, and an angle R that is formed between the reference line, and a straight line that passes through the axis and a rear end of the outer circumferential surface of the drill body in the drill rotation direction, is set to be within a range of 0.8≦F/R≦1.3.