| 摘要 |
PURPOSE:To make it possible to foresee breakage of a small diameter drill caused by an abrupt increase in cutting torque during drilling a small diameter hole, by detecting a rotational phase difference between a chuck and a spindle which is generated during the drilling. CONSTITUTION:A drilling device has a magnetic coupling 4 coupling between a collect chuck 2 and a spindle 5. Accordingly, if chips are jammed during drilling and therefore cutting torque is increased, the rotational phase difference between the chuck 2 and the spindle 5 is increased associated with a slip in the magnetic coupling 4. Further at the moment of the rotational phase difference exceeding a preset threshold, an evaluating device 16 delivers a drill 1 breakage warning signal to a drilling depth control device 17, and therefore, a motor 12 provided with an electromagnetic brake is stopped to stop the drilling. Further, the motor is reversed to retract the drill 1 from a workpiece so that the chips are discharged. Thereafter, the motor 12 is normally rotated to drill the workpiece again. |
