The connection to the uprights have not been decided yet. As I said, this is a design build.
By the way, then this is my fourth machine I will build. This time a smaller machine so I can have it in my garage, and still do other kinds of work in it.. :P

AdCNC
The rails are already mounted on top of a welded on piece of steel, which will be machined flat to true up the rails.
A Datum edge, is that a straight edge I can mount one rail along, so it will be true to the surface of the machine?