[DICKEYBIRD]

Heavy steel is good, but I would prefer to see (quite) a few more bolts everywhere than are shown. Some dowels, reamed after bolting, would be an excellent idea too - as you mentioned.

On which subject - all mating faces need to be machined smooth. Mill finish would walk all over the place. What to do about the underside of the table where the angle is shown - awkward question. Going for the extra width might not be worth it after all.

Whether it is best to have the gantry at one end, as shown, rather than in the middle, is another matter. You would need a really long overhang to get to the other end of the table, and that would worry me. Maybe I am a bit conventional?

Thanks Rog for warning me about the finish of the mating parts. That never crossed my mind, yet another time consuming but necessary chore. What about a roughing up the mating areas & applying a structural epoxy just before the final bolt up?

The final position of the fixed bridge will be determined by the total "stack up" of the X-slide components. The spindle axis will be located at the center of the table & the moving X-table's movement will be equal in both directions.

As suggested by Pete & others, I'm changing the design to incorporate longer vertical posts that bolt to the table legs with spacers. This will allow me to use my existing 3" square tubes to connect the posts and serve as mounts for the linear rails. With the addition of a 2" square tube placed across the junctions of the cross tubes it will be "Strong, like bull."