Quote Originally Posted by Voicecoil View Post
Something else to think about..... 6" x 3" x 3/8" box section (available off the shelf): Ix = 352, Iy = 1152, torsion constant (J?) = 823 - and about 1/2 the price of Item 160x80, though you obviously have to drill some holes A lot of the slotted structural profiles don't seem to be that amazing torsion-wise, I guess it's because a lot of the metal is a fair way inside the extrusion, whereas in a box section it's all at the outside, where it does most good.
Cheaper yes but it's not better unless it's prepped correctly and even then it's much more resonant. The profile is generally much flatter than box steel which isn't flat in any direction and it's less resonant, it's a lot easier to work with and does the job fine.

Torsion isn't an issue until gantry width gets wide and even then if sized correctly profile works fine for routers.