There are a number of occasions when the ability to turn the lathe spindle by hand, rather than using the motor, is very useful. A good example is turning to a shoulder with the fine feed activated. Here the slow speed and the ability to stop at exactly the right point are important. If this is done under power, then there is always a risk of crashing the tool into the shoulder. Another example is when cutting screw threads where it is important to stop the tool in a run out groove. Again, the slow feed, the ability to stop quickly and the tactile feedback when the tool enters the run out groove are all helpful.
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