I just want to say "thanks" to routercnc for this very useful design tool. It has quickly helped me to make some choices on the gantry design. I was surprised at the efficiency of box sections over simple plate, which most aluminum deisgn home routers / millers use. I had trouble with commercial extrustion section, but found the formulae in the "item" (Bosch - Rexroth) catalogue for deflection and torsion. There is also a free useful program "Tech Toolkit" produced
http://www.8020.net/Design-Tools-26.asp by the American outfit 80/20 which calculates the deflection for their profiles and you can define your own sections in it if you know the material and moments of inertia. Overall well done and so useful!. Measure twice cut once eh!!!!