Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

Actually the square collets are the nicest. Centering small square stock in the 4 jaw is a pain.  With my lathe I can freely switch from 3 Jaw chuck, 4 Jaw chuck and two different kinds of collet systems.  Whatever is best for the job.

Yes, turning the stem as you describe isn't that hard as long as you have a decent die holder for making those tiny threads at the end.  The biggest change from the plans is they use an o-ring for sealing the valve turny-bits assembly that screws into the valve body.