| 摘要 |
A plurality of cutting oil feed holes extend from the proximal side towards the distal side are provided in a drill body located on a reference line that extends towards a circumferential central portion of an outer circumferential surface of the drill body split by a chip discharge groove from an axis in a cross section orthogonal to the axis. 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. Two or more openings of the cutting oil feed holes are provided in one cutting edge as the plurality of cutting oil feed holes are formed in the vicinity of the intersection ridgeline portion between the distal flank face and the second thinned face.
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