| 摘要 |
PURPOSE: To prevent the drop of the strength of a cutting edge used for a furtive groove machining of the corner part of a stepped round material. CONSTITUTION: The upper surface 2 of a throw away tip 1 has an outline shape formed by that a circular arc beyond a semicircle is projected from two sides facing each other of a square. An escape is given onto a peripheral surface 5 contacting to a circular arc shape cutting edge 4. The escape angle of the peripheral surface 5 is formed so that an escape angleβof the maximum width of the tip may be biggest and it is setting smaller gradually and continuously as it approaches to a tip and it may be the smallest escape angleβ' at the tip part of the tip. Consequently, a conical body which is converged to an elliptical arc 7 toward a lower surface 6 is formed. Further, this conical body is formed up to the way approaching from the upper surface 2 to the lower surface 6 and a cylindrical body 9 is formed on this lower part. Additionally, a chanfering is applied in the lower surface 6 side so as to become wider gradually as it approaches from a tip end toward a rear end.
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