Any sugestions how to build my gantry

[Tom J]

So what is the your conclusion exactly? That 6Nm is not a big deal?

...yes, not big deal as I did proportion wright, few cm in wrong way and is double that

I believe that all very much depends on:
-the friction of the bearing blocks, in that case excellent. carrying capacity is much bigger than to have in mind in our case.
-the exact placement of the Z and gantry so the center of gravity is so that spreads the total weight of both equally on the bearing blocks.
-at what height the ball screw moves the gantry , ideally this should be the height of the cut.

friction of the bearing blocks is negligible for calculations as you do not have reaction in direction of movement - they slide

Ball screw location is important - means nut bracket have to ideally between blocks and in center axis of travel - no additional torques. I did mine like that, much more complicated but is worth it

So i will still separate them to form a 300mm from end to end. At the end its no more than 50-60euro worth of rails and steel for even a big machine.

As i see it, most of the designs in forums and even commercial ones, suffer from the ball screw not being where it should be, due to this and that. And it should near the level be where the cut is. That also is valid for the X / gantry / . Thats why the L gantry design and the ball screw in the middle of rails work very good.

Agree, firstly I was trying to gain every mm of travel, than I start sacrifice that for more important aspects like - stiffness rigidity ect.