PURPOSE: To provide a long-lived end mill which, in removing the influence of a branch point C, the occurrence of the breakage and chipping at the outer peripheral corner of an end cutting edge part is few.
CONSTITUTION: In an end mill having end cutting edge parts 1, 2 with the first and the second cutting edge 3, 4, a branch point C between the first and the second cutting edge 3, 4 is positioned more backward than the center line D of the end mill in the direction H of its rotation to make the height of the branch point C lower than a middle low gradient line A. The middle low gradient angle is less than 2°, and the second cutting edges 4 of the end cutting edge parts 1, 2 bend concavely in the direction H of the rotation of the end mill. The lengthening of the life of the end mill and the improvement of the roughness of a finished bottom face can thereby be facilitated.
TAKIZAWA TOSHIO
KITAURA SEIICHIRO
