Hi Dan, If you have a lathe then screw cutting is fairly straight forward, but internal screw cutting has to be approached with a bit of care regarding when the tool stops for obvious reasons
This vid shows the process, but this machine has some sort of attachment to auto-stop;
https://www.youtube.com/watch?v=usgYuEwe2AU
This one covers internal;
https://www.youtube.com/watch?v=olC9xyHheDU
Tons more on the tube and you will see already everyone seems to differ...For example on my little lathe at work when screwcutting I leave it in gear, pull the tool away a tad when stopped, then put into reverse to back out to then put the tool back in far enough to take another cut and then start in forward again, ie. I never dis-engage the lead screw. I have on occasion had the indicator wheel come out of engagement and have ruined a job, so this way is fool proof!
I have the advantage of a digital readout, so can see easily how much I am cutting, but have done plenty on machines without this luxury.
Obviously internal cutting to a blind hole has to be approached carefully, with plenty of attention paid to avoid a shunt...I had a 600 a while back, but can't remember if the thread was full depth, I am guessing not, which makes it much easier to do.
The tube is a great resource for home machinists, try looking for barrel crowning for example, everything is on there, but always best to watch a few different people to see different approaches.
First attempt at internal cutting would always be easier with tube as the second guy shows, to get your head around winding the slide toward you to remove material etc.
Have a play, nothing to lose, loads to learn, just go easy and take care.
ATB, Ed