Made of aluminum, Made for aluminum: Would love design critique!

[gamingan]

In case it is not obvious you have trapped the long axis rails between the gantry sides, which means you cannot easily control the pre-load on them when it is all assembled.
As drawn the side extrusions which sit on the bed - one of them needs to be adjustable laterally so that the pre-load on the rails can be set. Otherwise if you bolt this together rails may wear prematurely or bind.

Consider going one step further and putting the rails on the top of the side extrusions, you can quite literally get rid of all unsupported gantry side arms and it is certainly easier for alignment purposes than side mount.

Hmm... I will try to go this route but I really prefer the rails mounted on the sides because it also does a bit of dust shielding. Is there any reliable strategy you can think of (screw-based adjustment perhaps?) to adjust/align things if I *HAD* to go with rails on the side?

And to be honest, I don't see how top-mounting the rails allows adjustment either... routercnc mentioned the need to do lateral adjustment, which I agree with, but how exactly does this become possible in practice for the case of top-mounted rails?

Zeeflybloy: Regarding flipping things (rails <-> bearings) on the Z-axis: Will check to make sure it doesn't conflict with any dimensional constraints I have, and give that a try.