Hi Psiron,

The double 100x50 box section gantry looks much better. If it is well tied in to the upright side pieces, then this may be OK. The next thing to flex would probably be the raised side rails upon which the gantry runs. Can these be joined across to each other at the far ends? This would block loading of the workpiece a bit, but is worth considering at least at one end. Or a big shear panel at one end to tie down to the under structure.

The video shows linear rails, which are a great help if you can afford the long lengths. The video example does not bind with the belts low down on the sides, and looks like it would cut OK too.

What do you mean by rhs instead of channel? If this is RSJ then this is also poor in torsion and would not make the best gantry. Run with the box section.

Good luck with it, and send out more when you have it.

Barry