I definitely like the adjustable version!
I know spindles are not supposed to have any significant run-out, but by the time something is threaded on, they do acquire at least a little.
So when one turns up a backplate, everything on it again ends up perfect concentric to that machine axis.
If there was any run-out on the spindle
, then cutting the backplate in effect left it behind in the join. Runout gets removed.
Unless, perhaps, between chuck dismount-remounts??
The result Basement Machinist got was so very good, it brings the 3-jaw to become very respectable. It comes to mind that this adjustable feature could also be used on a backplate that mounts a collet chuck.
Regarding the metal.
Basement Machinist mentions how much better is what he called "ductile cast iron" compared to "grey cast iron" in that the ductile version makes little chips, whereas the grey type makes a messy powder. That would be graphite carbon mixed with silicon stuff. The "ductile cast iron" is possibly much the same as "cast semi-steel" that South Bend lathe beds are made of - but I don't really know. His motivation was purely about the messy contamination. "It gets everywhere and is a pain to clean up".
This Old Tony mentions that cast iron is traditionally used for backplates, he thinks to ensure the metal in the thread is not too similar, and so won't seize or gall. Even so, he just uses the steel he has handy, and has not had any problems. Wikipedia mentions grey cast iron is good at damping vibrations.
Like This Old Tony, I more often have to use what I can salvage, score, connive, or have to hand. I has me wondering whether the old brake discs from when I replaced them on my car might be useful. If that is a bad thought, fraught with problems, then please, someone let me know now!
