[ger21]

I didn't realise it was 80". Yes, I was talking about putting a torsion box between them. If you sandwiched the 2 pieces with plates, I think you would need to bond them with epoxy to stiffen it up. If you just bolt the plates on, it would still flex more than if bonded on. I think you could build it lighter with maybe 3/8" baltic birch plywood skins, and about a 4" x 4" gridwork inside the 2 skins. You could get away with smaller 80/20 at the top and bottom, too. But I think you'd have to go at least 12" tall on the wood framing. Taller is better. My Y axis I show in the link I posted is 40", and way overbuilt, but there is no way it could sag without several hundred pounds on it. It ways maybe 15-20lbs. I could have built it half as light and just as strong. If it works out well, my next router will have a 60" Y using similar construction. I already have the IKO rails for it.