Tapping apparatus and method

A tapping apparatus for cutting an internal thread in a workpiece with a tap, comprising:

• a spindle to which the tap is attached;
• a spindle motor for rotating the spindle;
• a detection device for detecting a load acting on the spindle motor during a tapping procedure, wherein the tapping procedure includes a cutting process, in which a workpiece is cut with a tap, and a withdrawing process, in which the tap is withdrawn from the workpiece;
• and
• a computer, wherein, in the withdrawing process, the computer performs an acceleration step to accelerate the spindle at a predetermined withdrawing rotational acceleration rate and a deceleration step to decelerate the spindle at a predetermined withdrawing rotational deceleration rate,
• wherein the computer compares the load detected by the detection device with a predetermined referential load to detect a relative cutting load acting on the tap, and
• wherein, when the relative cutting load exceeds a predetermined acceptable level, the computer stops the spindle to discontinue the tapping procedure and thereafter performs the withdrawing process by accelerating the spindle at a rotational acceleration rate that is smaller than the withdrawing rotational acceleration rate and decelerating the spindle at a rotational deceleration rate that is smaller than the withdrawing rotational deceleration rate.

A tapping apparatus for cutting an internal thread in a workpiece with a tap, comprising:

• a spindle to which the tap is attached;
• a spindle motor for rotating the spindle;
• a detection device for detecting a load acting on the spindle motor during a tapping procedure;
• and
• a computer, wherein the computer compares the load detected by the detection device with a predetermined referential load to detect a relative cutting load acting on the tap,
• wherein, when the relative cutting load exceeds a predetermined acceptable level, the computer stops the spindle to discontinue the tapping procedure, and wherein the computer starts the tapping procedure for the same threaded hole from the beginning, and
• wherein, if the number of the tapping procedures performed for the same threaded hole is more than a predetermined number when the relative cutting load exceeds the acceptable level, the computer judges that the life of the tap has expired and discontinues use of the tap.