Quote Originally Posted by valdis034 View Post
I am not so used to this machine terminology, but cross bracing in my case are these aluminium extrusions which are joining longest (x) axis, yes?
And if i understand right i cant have middle legs because that cross brace between gantry, but that aplies only for single ballscrew on x axis. I am going to have two ballscrews on x axis driven with belts by separate motors.
YES. But 2 screws will mean having them on the outside where they are unprotected from Debris. The Cross brace allows you to keep them under the table out the way.

Quote Originally Posted by valdis034 View Post
The bed probably i will have several 40×40 extrusions attached to the main frame, and on those extrusions i think should be good to have sacrificial plywood or mdf.

Does that sound good?
No 40 x 40 isn't strong enough really you want 80 x 40 for the bed supports. Or at least two with 40 x40 filling the in betweens.