| 摘要 |
PROBLEM TO BE SOLVED: To amplify a shearing action of a main cutter and to also effectively break a reinforcing bar, by distributing to increase a mass from a central axis of a drilling tool toward an outer periphery of a thread in a predetermined mass distribution at least a part of a lengthwise direction of the thread. SOLUTION: The drilling tool 1 comprises a drill head 2 having a cutter plate 3 made of a hard metal, and discharge grooves 6, 7 limited at threads W provided over a part of an overall length 1 of the tool 1. The plate 3 has a main cutter 31 forming a predetermined cutting angle at the axis A of the tool 1, and the angle is different at an angleαfrom the axis A of the tool 1 at a gradient S of the thread W. The thread W has a predetermined mass at least at part of the lengthwise direction, and the distribution is increased in its mass from the axis A toward the outer periphery of the tool 1.
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