half nuts close, the thread still goes drunken at the end

Bench 9, not the Logan I sold. 16 tpi, external, starts clean and the last few threads look torn. Half nuts stay closed. I remember this argument from years ago and I am trying not to repeat it badly. Tool is HSS, on center as far as a rule tells me. Stickout is short. I did cut a groove.

If the pitch is right and the crest is torn only at the end, you're running into the groove with a tool that's still loaded, or the groove isn't wide enough and the tool is rubbing the shoulder. Check the groove width against the tool, not against the idea of a groove.

Groove was narrower than the tool. I widened it. The torn crest went away. I did repeat an old argument, just with a shorter lathe and less dignity. Leaving it up.