I need to make from scratch an Acme form tap for a 1/2 ID nut, does anyone have / know the T&C grinder settings, ie relief angles etc for this type of job. Somewhere in the distant past I saw a set of tables for such but can't locate then anymore. TIA.
Grinding an Acme tap
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I hate to mention this (particularly since you sound like you know what you're doing) but you can get away with no relief if you're not tapping anything long. I made a 1/2-8 LH ACME from A2 that works well enough for my purposes, the only relief was mill the top away for back relief to about .020 of the tooth face and to lightly stone to the tooth, there's no side relief at all. If I'd cut the flutes right the tap would work very well, as it is it need to be cleared quite often.
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