Hi Jake - I don't think the stiffness of your Z axis plate matches the capability of the machine, especially when its down. The rest looks very good. It needs to be quite a bit thicker. Look up the Maximus thread I spend a lot of time looking at the Z axis stiffness in that. Do you have someone to machine the gantry after you weld it? It will change shape quite a bit with those long welds.

If you send me the step model of the columns, bearings (or zip it and publish here) , gantry and z axis I'll run it in an FE program to see how stiff it is. Put it in the max down position, with Z in the midway gantry position....Do you want to cut aluminium ? Peter