X gantry material

Hi, can anyone more experienced give me an opinion on what should I choose as a gantry for a DIY build?
Coming from workbee cnc, I did a lot of upgrades making it a pretty solid machine.

But now I am building something slightly more rigid. 40 series extrusions instead of Vslot ones, full aluminum bed, 20 mm thick plates, etc.

Currently I have a 80x60x3 steel box section as the X gantry. How does it compare to a 80x160 or 90x180 mm aluminum extrusion?
The Fusion360 simulations say they should perform about the same, but I am not sure if I can trust my simulation setup...

The question is should I use the steel gantry on the new build (perhaps packed with non shrinking grout) or change it to the big aluminum extrusion? Or perhaps go with bigger steel like 80x100?
The gantry span is not big, just 1000 mm.

If any more info is required I am happy to provide it.

Thank you.

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The outside dimensions give a gantry beam most of its stiffness, especially the vertical. And steel is a lot stiffer than aluminum. A box beam is stiffer than a T-slot extrusion, since it's the outer skin that counts the most in resisting flexure. So if your design has room for a beam with a 90 x 180 section, a box beam of that dimension would work best. The steel is going to be heavier than the aluminum, which is something to consider, since the momentum will work against you, especially when changing directions. Filling it with concrete grout would make it a lot heavier. Interior plates would be preferable.

Unfortunately the design won't fit that large steel box section due to the ballscrew drive design I have. Maximum I can fit is 80x80 or perhaps 80x100. Aluminum I can fit larger but I'd have redesign the X and Z axes a bit.
So I'll probably stick with steel and see how big I can fit on it as I already have the aluminum gantry plates ordered.
As for the grout or epoxy granite I know it adds weight, but I am also hoping for vibration dampening.
I'll post some photos and fusion images tomorrow to show it better.

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