Quote Originally Posted by blackburn mark View Post
3m x 3m is quite a large machine... i'm not sure anyone has built one of that size on this forum ?
I don't recall any that size here. You can get 3m long rails rails easily, but if you decide to use profile rails then it will be hard to align them over that distance. You're getting into mounting the rails on self levelling epoxy territory. The SBR series rails tolerate a lot more misalignment than the profile rails, so that option would be a lot easier and I'm confident you could make a strong enough machine that size to cut aluminium with them. The gantry clearly needs to be stronger than the current design if it is extended to 3m. You may want to consider placing the Z-axis between two beams with the rails on their inner faces.

With 3x3m you would also need rotating ballnuts on both X and Y. Just in case you've not already found it, there's some ideas about how to mount a rotating nut here. It sounds like you might have a milling machine so as long as you've got a boring head or lathe you can make them.