SCREW WORKING DEVICE

PURPOSE:To provide a screw tapping device which can carry out the stable tapping work in a short working time independently of the working speed. CONSTITUTION:A main spindle accelerating speed calculating circuit 24 outputs the max. accelerating speed As of a main spindle which is the value obtained by dividing the max. revolution speed Sm of the main spindle by the min. time St necessary for obtaining the max revolution speed of the main spindle, and a Z-axis accelerating speed calculating circuit 25 outputs the max. Accelerating speed Az of the Z axis which is the value obtained by dividing the max. shift speed Zm of the Z axis by the min. time Zt necessary for obtaining the max. speed of the Z axis. A comparison circuit 26 compares each max. accelerating speed As, Az, and outputs the less value as the accelerating speed A, and an acceleration//deceleration control circuit 27 acceleration/deceleration-controls the distribution pulse Pz according to the accelerating speed A obtained by the comparison circuit 26. Accordingly, even in the case where the tapping working speed is a high speed, the drive over the capacity of a motor is prevented, and overshoot, etc., can be prevented. Further, even in the case where the tapping working speed is a low speed, the necessary time for obtaining the set speed is shortened, and the working time can be reduced.