Choosing between alternative X axis bearings designs

[JAZZCNC]

ADJUSTMENT ADJUSTMENT ADJUSTMENT... I've said this many many times in posts but I'll say it again because cannot be stressed enough.

With this fixed gantry design, you are going to need plenty of adjustment. If you weld up the gantry completely and especially if welded to the base frame you won't be able to adjust the planes the rails sit on in relation to the other planes.
Any extra time spent thinking about how you can build in adjustment will pay back big time when setting up the machine and the accuracy you will get from it.

Regards the 50mm with 3mm box section then like I said in other thread, it's spaghetti-like properties mean you really will need to brace it good. Not so much for strength but for rigidity and resonance. The thin wall means it's resonant which causes vibrations at the tool, yes you can fill it with sand or concrete-like some have done, but this won't help a poorly designed and braced gantry.
This stage is critical to get right because it's the foundation everything else references from, Wobbley foundation = Shit machine simple as that.!

There's 3 key areas to building a great machine, get any one of them wrong and the machine will suffer.
#1 Base frame
#2 Strong Z-axis
#3 Good electronics.