Hi Vic
FEA looks good, I need that program.....looks so much quicker, dose it also generate a list for validating? How does it calculate the fixing type at the bearings or is it asuming a rigid connection?

From the analysis it looks like the z axis plate is the weakest as its only a 2d plate. Id mount some angle on it parallel to the spindle for strength.

For the C channels on the long axis you could flip them 180 deg so the web is on the out side and directly below the angle also it might be worth getting some unequal angle for the vee bearings, something with only 10 or 15mm upstand would be much better. Alternatley you could stick with the original config but add a plate to close the channel, this could extend up and bolt in to the angle as well to help brace them, two birds one stone etc.

This would also be a good idea for the x axis (?) as the open C channel is weak in torsion, need to move the ballscrew tho. As a final observation the vee bearings are only bolted to the end plates, it might be worth incorporating their mounts with the C channel uprights.

Anyway good luck.