These drawings are crude and may change before the final product. They may not be to scale yet to save picture space.For the z axis it is going to be a square cage with the router in it and a square cage around that will have the slides for y axis and linear rails for z axis. The linear rails are to scale but the table size one is not i need to finish my router mount witch is going to determine the length and width of the y and z axis. I quite havent decided what to do with the x axis the 4' span. It could be either design with flat welded or just square. I have not decided on what to support the x rails with yet either at first it will probably be mdf or 3/8 .09 square at a set distance.
Z axis 12"
X axis 48"
y axis 24"
That is the table cutting size so they lengths will be bigger than those dimensions but i can mimic your lengths by supporting the rails and testing them.