sgspenceley submitted a new resource: Extra strong corner brace plates - Strengthen your OX Y extrusion & improve your GT3 belt attachment Read more about this resource...
I suggest using, 1/8th mild steel or 1/4" aluminum. I used 1/8" mild steel which was laser cut. Depending upon the bumpers and proximity switches you may want to consider adjusting the size of the outer holes.
A few example prices. 1/8” mild steel $8.75 US Each 1/8” Alum 6061 $13.50 US Each 1/4” Alum 6061 $16.75 US Each
Steve, I've been looking at a lot of designs, the original OX etc, that all follow what you have done with a few of yours, namely you join the frame stacked on top instead of butting them in a low flush profile. What is the advantage of raising the x extrusions above the floor so to speak is it just for v track clearance of the gantry? In your linear design also the bed is under the x drive motor. jack