Quote Originally Posted by Jeremy View Post
... Thanks for pointing me in the right direction with the deflection calcs - I hand't thought to just apply simple beam theory to this problem!

Jeremy
You're welcome. I used the Framework program (mechanic.zip) at http://members.ziggo.nl/wolsink/ to do a rough 3D analysis. Although it doesnt allow you to model the supported rail joined to the box section, I simulated it by creating an arbitrary shape comprising a 30mm high, 15mm wide steel block on top of a 40 mm x 30mm box.

One way to counteract the vertical torsion is to make the gantry sides solid and put a diagonal brace from the side to the cross beam. Obviously too big a brace will compromise the vertical work envelope.