I've been doing some thinking in my free time about evolving my design, and I realized I've been modeling my frame somewhat incorrectly. I have the z axis fixed to the gantry through the linear bearings in x, y and z directions. When I first started out, this was probably somewhat realistic. While the bearings obviously would not be supporting the z axis in the z direction, the ball screw would be mounted fairly closely to the bearings so the vertical load would still be applied to the gantry in roughly the same spot. However on my newer designs such as the sketch in post #14, the ball screw will be attached to another frame on top of the gantry which will distribute the vertical load to the outer portions of the gantry instead of the middle (assuming this works well when I model it). This means the vertical forces that I'm currently modeling as being transferred through the z axis bearings are not accurate at all and are possibly causing me to over design my gantry. So now I need to figure out how to model and constrain the z axis so it's close enough to reality to be a useful design tool. Looks like I'll be learning some new ANSYS techniques...
CNC mill build thread: http://www.cnczone.com/forums/vertical_mill_lathe_project_log/110305-gantry_mill.html