PURPOSE: To prevent the damage of a drilling tool during drilling work and to improve its drilling speed in the drilling tool whose tip is protruded to the tip of a tool body and given vertical impact for executing a drilling action.
CONSTITUTION: An oblique face 3 is formed on the peripheral part of the tip face 2 of a bit 1, and plural number of tips 4a severally having a cone-shaped part are plantedly provided on the tip face 2 as the cone-shaped part is protruded. On the other hand, plural number of tips 4 severally having a semi-spherical part are plantedly provided on the oblique face 3 as the semi-spherical part is protruded. In this case, the radius of curvature at the tip part of the tip 4a plantedly provided on a tip face is set up to be smaller than the radius of curvature at the tip part of the tip 4 plantedly provided on the oblique face, and the biting action of the tip 4a plantedly provided on the tip face into the ground is therefore improved, and the occurrence of stress concentration to the tip 4 plantedly provided on the oblique face becomes difficult.
HAYASHI TAKESHI
TSUJIMOTO KATSUAKI
