| 摘要 |
PURPOSE:To improve a centripetal property, and to reduce the thrust load at the time drilling by forming a flank extending from a cutting edge into a curved surface very close to a flat surface, and by forming a cutting edge continued to the cutting edge on the tip of a web part. CONSTITUTION:A cutting edge 3 is formed on the end part of a land 2, and a flank 4 is formed continuously. When the flank 4 is formed into a predetermined width, the flank 4 comes in contact with an inner edge 7b of a grinding wheel 7, while a drill 1 is moved along the edge 7b, and a second flank 5 is formed on the left end side of the land 2. At the time of forming the second flank 5, a sharp raised part 5a is formed on the front of the second flank 5, and the cutting edge 3a is formed on the chisel edge on the front end of a web part. The centripetal property can be improved, while the thrust load at the time of drilling can be reduced. |
