Terry,
That's how the crusty old toolmaker I mentored under did it; kept the half nut engaged for metric threads. He HATED metric threads.
Now..... On my Hardinge HLV-EM, it's just a matter of flipping the E-M dial to "M", and I'm good to go.
Everything John just gave you is spot on, EXCEPT.... (and this is more a matter of preference)....
I like to set my compound about a half degree shy of the thread face angle. This ensures you don't "walk away" from the thread face as you advance the compound. On my ProtoTrak lathe, the threading cycle defaults to 29.5 degree advancement (you can change it, which you would obviously have to do for anything other than a 60 degree included thread profile), so they must agree with this approach. I think most other CNC lathe MFRs do as well. Unless you are doing a REALLY deep thread profile, there is little more than a slight skim against the "non-working" edge of the threading tool.
One other thing.... I like to run my dials to zeros. Meaning, I advance the compound to zero and I have the X-axis dial set on zero when I'm chasing threads. After you've cut your threads (hopefully oversized initially) and you check your pitch diameter, if you have to make an adjustment, I'd advise doing it with the X-axis dial and re-cutting the thread, starting over with the compound advancement to zero. This will save you from forgetting that the compound will give you almost double the change you dial off. I had to learn this the hard way. This will also keep you from slamming into a shoulder, if your close enough to worry about it (like I often am), as the X-axis dial doesn't advance the Z-axis location the way the compound does.
Taking notes?
Thanks. Brad.
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