NC GRINDER

PURPOSE:To enable compoundly a cutting edge of a tool or the like to be indexed and ground and a cylindrical surface or the like to be continuously ground by giving selectively index position locating rotation and high speed continuous rotation to a workpiece spindle by the operation of a change-over means. CONSTITUTION:In locating an index position, an electromagnetic clutch 7 of change-over means is excited to connect a workpiece spindle 1 to a gear transmission mechanism, drive a index rotation driving DC servo motor 10, index rotationally the workpiece spindle 1 through a worm gear 9, worm wheel 8, drive shaft 5, electromagnetic clutch 7 and gears 6, 2 of a gear transmission mechanism and index grind the cutting edge of a tool or the like. On the outer hand, in the continuous rotation, the electromagnetic clutch 7 is demagnetized and the workpiece spindle 1 is disengaged from said gear transmission mechanism while an AC motor 13 for continuous rotation driving is driven to continuously rotate the workpiece spindle 1 through a pulley 12, belt 11 and pulley 13 of a belt transmission mechanism and continuously grind a cylindrical surface or the like.