On Wed, Aug 28, 2024 at 07:34 PM, John Dammeyer wrote:
Or just use taps and dies.
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If you find yourself in a dimensionally confused environment, as I am sometimes, with metric and inch threads, sometimes deliberately obscure (never did find ?" 27 tpi taps or dies when I needed them), and add in things like optical threads (large diameter, fine pitches), BSC (British Standard Cycle threads), Pg conduit threads and finally the oddity of BA threads - pitch is 0.9^(BA number) so it goes 1.0, 0.9, 0.81, 0.729, 0.6561, 0.59049, 0.531441 - and that only gets us to 6 BA - 16 BA has been seen in captivity. Yes, you can get taps and dies for all sorts, but the most obscure I have seen so far was a full set of taps and a die for M39.5 ¡Á 1.25 Left Handed. I dread to think what that cost. I also know, from looking at the job it was used on, that a much more standard thread could have done the job (using an M40 ¡Á 1.5 KM8 bearing retainer nut with a tab washer to lock it).
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So when screw cutting on the lathe? NC could give great flexibility in choice of diameter and pitch, well beyond all the drawers full of taps and dies my mate has accumulated in his workshop over the last fifty years. And saving hours searching for the odd thread you were sure was there, but in the end it wasn't.
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All this applies to thread milling, but I can't see how that would succeed on any of the small Unimats in milling format.
