To improve polishing efficiency by applying the constitution wherein a work shaft fitted in a liftable polishing shaft chest is made to turn in either direction on a rack and pinion and the rotary direction of a workpiece is changed in a short time for the easy control of a polishing direction on the move of said chest. When a workpiece has been held, upper and lower rotary discs 8 and 9 come down, a workpiece 31 is inserted in abrasives and a polishing shaft drive motor 14 is operated, thereby actuating a drive shaft and a crank arm, and causing the reciprocating turn of a rack. Concurrently, therefore, a pinion gives a reciprocating motion, while a polishing shaft 23 and the workpiece 31 giving a reciprocating turn. When the workpiece 31 is flat and made to agree to the dead point of the crank arm in a direction orthogonal with the flow direction of abrasives, the sliding speed of the rack becomes minimum at the aforesaid position in the motion of a crank mechanism. Namely, the rotary speed of the workpiece is minimum and time is prolonged when abrasives are orthogonally in contact with the workpiece, thereby improving polishing effect. |