HI Nealieboyee

Have you considered making the headstock separate? That would make preparing the mounting surfaces for the bed rails somewhat simpler. It would also allow the headstock to aligned after it is completed. threaded steel sockets can be cast in the bed then threaded studs in slightly oversize holes in steel sleeves cast in the head stock can used to bolt and align the head stock initially with packing for testing later the void between the castings can be filled with epoxy. Stephen Gotteswinter shows this in a video. https://www.youtube.com/watch?v=U7Qs-J2swIc

The same method is cited here in this seminal CNC paper https://pdfs.semanticscholar.org/548...5a7da2fee8.pdf

This is the actual machine designed in the paper! https://my.mech.utah.edu/~bamberg/re...mberg-PhD.html

And Peter at Edge Precision has one..https://www.youtube.com/watch?v=akF7jvDRxH8

Check out the rest of his videos..https://www.youtube.com/channel/UCCk...PY7OMxQ/videos

No back to your lathe......

The bed rail supports I assume made from steel cast in position within the bed mold will need to be flat and parallel, While it is possible to scrape them to perfection having done it for a milling machine I am working on it involved a lot of time and physical effort. Your bed would fit nicely on a surface grinder or a mid size mill. A headstock cast in position might make this difficult.

FWIW you may find this link to my mill project interesting It is stalled at the moment due to work commitments. I hope to get back to it over the holidays. https://www.model-engineer.co.uk/for....asp?th=139042

CNC? Have you considered incorporating step motors to drive your screws. in your design? Some have a shaft at each end allowing you to attach a hand wheel to the back end of the motor. This would allow you to start with manual control and later convert the machine to CNC The manual control can be left operable.

The low friction linear bearings may create back driving issues. Without the "stiction" that the dovetails found on most lathes provide. Maybe if steppers were fitted the screws could be driven manually with a pulse generator instead of a hand wheel. I have seen small boards to do this on the net.

The natural progression from this would be to fit ball screws instead of Acme screws. Yes more expensive but thanks to Asia maybe affordable.

Regards
John