| 摘要 |
PROBLEM TO BE SOLVED: To provide a drill bit by which core vibration of the drill bit can be reduced when perforation accompanied by striking cutting is performed and roundness of a drilled hole can be improved. SOLUTION: In the drill bit in which a plurality of cutting edge parts 3a, 3b and 3c are formed on a cutting edge tip 3 made of a carbide-tipped alloy fixed on the bottom end of a drill main body and a joined diagonal line of a cutting face 5 and a relief face 6 formed on each of cutting edge parts 3a, 3b and 3c is made to be a cutting edge 4 and each of the cutting edges 4 is butted at the top of the cutting edge, at least one of angles between adjoining cutting edges 4 is made to be an unequal angle to the angles between other cutting edges.
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