| 摘要 |
A drill to cut hardly machinable materials has major flanks extending in a backward direction of rotation from major cutting edges with an ascending slope and ultra-hard cutting grains adhered to said major flanks, at least. When the rotating drill contacts the work-piece, the ultra-hard cutting grains adhered to the most backward part of the major flanks to the direction of rotation cut the work-piece at first. As the ultra-hard cutting grains of the major flanks drop off by the cutting, actual cutting parts move to adjacent part forward of the rotation of the major flanks. Finally, major cutting edges take over the cutting of the work-piece.
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