5. Operation of thread cutting

Thread taps take off material from the periphery of the bore hole. This is done by permanently turning them forwards and backwards alternately with the help of a tap wrench.

In doing so, lubricating and cooling agents must be fed in.

Figure 9 - Thread cutting

The forward turn should amount to half a rotation approximately, the backward turn to a quarter-turn. The material is squeezed and removed within the thread groove the total quantity of chips sticking in the thread grooves.

The backward rotation causes the crushing of the chips, so that they can fall out of the chip grooves of the thread tap.

Note:

The backward turn up to the crushing of the chips, with medium hard and hard materials, is marked by a clearly noticeable jerk. Only then one can be sure that the chip is really broken.

If one fails to crush the chips continuously, the thread grooves and chip grooves become stuffed up. The thread tap becomes jammed and breaks. It can no more be screwed out of the bore hole. The same applies to the cutting of external threads.

Describe the movements with the cutting of threads.
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Why is it necessary to move the thread tap or threading die or die-stock, respectively, backwards at regular intervals?
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Why must lubricating and cooling agents be used?
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