Stell frame cnc 1500X1000. Adjustable table your opinion please

[JAZZCNC]

This is how I plan to do my top rail.
legs 50x50x3 steel box
top rail 100x50x3 steel box
6mm or maybe 10mm plates welded on top of the legs and welded to the underside of the top rail.
Bolts will pass through the plates on the legs and will screw into threaded holes in the top rail plates and right through into the box.
These joints will be shimmed to level the top surface of the rail and to ensure both sides are in the same plane.
Before bolting the pieces together I will grind the surfaces of the plates flat, checking with a straight edge
It would be easy to weld 2 further intermediate points if this found to be flexing.

That's pretty much I do my rails but to make life simpler and do away with grinding and shimming etc I spread a layer of Epoxy putty on the bottom plate. Then I put layer of plastic between rails and plate then lightly tighten together pushing some excess out then set the rails on same plane and parallel etc. The putty gives plenty of time for adjustment and dries hard has metal.
It has dampening quality's has well so helps with vibes transferring thru frame. It drills and taps easy and fills any voids, I can shape to match radius etc and it easy grinds and sands if needed.
When set 24hr later I have a perfect hard surface that sets rails exactly on same plane. The rails can be removed and go back exactly on same level so no messing around with shims etc.