| 摘要 |
PURPOSE:To prevent breakage of a tap, by a method wherein, when it is detected that a main spindle guide member is moved toward a mounting part, a motor is reversed to move a tape, mounted on a main spindle, in a direction in which it is escaped through a lower hole. CONSTITUTION:A male screw part 18 is formed on the outer peripheral part of a main spindle 16 of a threading unit 31, and a female part 20 is formed in the inner peripheral part of a main spindle guide member 19. When a tap 24 is collided with a position displaced from the lower hole of a workpiece or the tap 24 is collided with the bottom of the low hole of a blind hole to suddenly stop rotation of the tap 24 and exert an unreasonable force on the main spindle 16, even when rotation of a chuck shaft 25 is stopped, the main spindle 16 is rotated in a manner to slide over a joint 22 part. Through detection of elevating movement of the main spindle guide member 19, a motor 12 is immediately reversed to raise the main spindle 16. This constitution reliably prevents breakage of the tap 24 and damage of a workpiece.
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