As far as bolting two rails together, you’d have to drill holes in one rail and use the slot nuts. I’d think a bolt and nut every 8-12 inches would give enough support. I’m thinking if you used a 20x80 extrusion you might be able to mount the support rail to the maker slide so the support rail sits higher than the slide. This would have the benefit of shielding the slide from dust and chips. It looks like there’d be enough clearance.
What I’m really interested in when I get to expanding the xcarve beyond 1m x 1m is changing from the belts to bicycle chain and cutting replacement plates for mounting the gantry so I can mount it higher to increase z-axis.
—Just placed my order—