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A recent thread by another member has prompted this question. So rather than risk taking his off topic I shall start another thread.
It is something I have never needed to do. (though Jason will state I wasted a good bit of cast iron last week by not doing.)
I am presuming there is a correct way of doing this in the same way there are things to avoid when parting off for example. So what sort of tool shape is best needed and is there a practical maximum depth that this could reliably achieve.
Nick