| 摘要 |
A drill having an exchangeable conical tip end is provided to remarkably improve the preciseness and the machining quality of a drill by integrally forming the conical tip end and accurately and simply regulating concentricity and an engagement angle by a center engaging section and a key engaging section. In a drill, a conical tip end section includes a cutting blade(1b), a recess(1c), and a land(1d) on both sides, with a web(1a) being an apex. A cutting blade is mounted at a body. An detachable tip end section(30) is engaged with the body so as to be perpendicular to the lengthwise direction of the drill and integrally includes the conical tip end section. A center engaging section and a key engaging section are provided on engaging surface of the detachable tip end section and the body. Prominences and depressions are formed in the central engaging section. The key engaging section is symmetrically formed on the right and left sides of the central engaging section. The center engaging section has a center groove(13) and the detachable tip end section has a center protrusion corresponding to the center groove.
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