| 摘要 |
A drill including a columnar body that is rotated about an axis, a cutting edge that is formed at the tip end of the body, and a thinning edge that is formed continuously with the cutting edge close to the axis of the body, by having a thinning at the tip end of the body. The thinning edge is formed such that a rake angle of the thinning edge relative to the axis of the body changes depending on a location of the thinning edge, where the rake angle of the thinning edge close to the cutting edge is a positive angle larger than that close to the axis of the body.
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