| 摘要 |
a motor as a power source; a rotary body for forwardly or reversely rotating a fixed processing material in a clockwise direction by the operation of the motor; a steel ball contacted with the processing material, for forming grooves on the surface thereof; a retainer to which at least the one or more steel ball is inserted; and a piston rod coupled with the retainer, for moving upward and downward towards a hollow of the rotary body at which the processing material is fixed.
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