Hi,
when i said above for the plates i meant the gantry.

What would be the square steel box profile size? I calculated it many times and for steel machine/this size especially/ is best to use bigger profile 100x100x3 or 4mm and simplify the structure. I say always 100x100 as it is the max that could be handled and cut at home using dry saw or small band saw.
The benefits are:
-simpler
-easy to cut at home
-easier to solder
-stronger
-less metal for the same strength so cheaper

You could read more here and see changing the table design leads to substantial savings http://www.mycncuk.com/threads/5302-...highlight=tony

In fact if you have the means the bigger is better here.