I was thinking about your comments on knee automation and had this thought.
Do you really need to CNC control the knee in order to get the positioning
you wanted except maybe for an extremely few parts? Why not just put a DRO
of some type on that knee. Maybe not a fancy made for application one.
Just a simple digital caliper (over sized for your ap of course) like used
by a lot of the mini lathe guys on their tail stock. Or you could shop for
deals until you find a fancy DRO at an auction somewhere.

I'm dealing with a lot of these same ideas on the Hurco retrofit, and I
started with the concept of using an independent control just for raising
and lower the knee, but then I thought, "Gee. Its not that hard to crank,
and even if I do need to move it its only going to be once or twice during a
fairly complex part." If it were hard to crank I could throw any old DC
servo on it that's strong enough and power it from a variable voltage power
supply for speed to move and slow speed to position with a DPDT spring
loaded toggle switch. Maybe some diodes for protection of the switch.