| 摘要 |
PROBLEM TO BE SOLVED: To provide a twist drill for drilling a high-roundness hole in a workpiece and smoothly discharging cutting chips generated during hole drilling in the workpiece. SOLUTION: As the twist drill 1 has cutting edges 1A, 1B formed in positions nonaxisymmetric about an axis O, the two cutting edges 1A, 1B hardly resonate with each other during hole drilling in the workpiece, thereby suppressing the skidding of a chisel edge 1G from a rotation center of the twist drill 1, so-called a walking phenomenon. The twist drill can accordingly drill the high-roundness hole in the workpiece. Since two spiral grooves 1C, 1D having the same width are formed at positions nonaxisymmetric about the axis O as corresponding to the two cutting edges 1A, 1B, in particular, the two cutting edges 1A, 1B have the same rake angle, so that cutting chips generated during hole drilling in the workpiece are smoothly discharged along the two spiral grooves 1C, 1D. COPYRIGHT: (C)2010,JPO&INPIT
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