| 摘要 |
<p>A drill includes a cutting edge (6) having a ridgeline. The ridgeline has a part of an ellipse and a straight line. The ridgeline of the cutting edge (6) is formed straight along the tangent in the area of the tip, and is formed along the ellipse in the periphery. A margin (5) is formed continuously from a relief face (8) of the cutting edge (6).</p> |
