Thanks for the detailed explanation.

However i would like to design mine machine quite bigger, up to the point that i am tempted to reach and surpass the length limit of the ball screws on the long axis. I don't intend to do steel though. I wonder if i am right that with this gantry design + 2 nuts at each of the long sides/x/ i could go with longer 1610 screws, say like 1800mm or even 2000, cause if i separate the bearing blocks that move the gantry say 400mm that gives screw lengths like - (1800-400) /2 = 600mm from each side if gantry is in the middle and 1400 if gantry is at one end, which more or less i assume is the limit before whipping occurs.

So, from your point of view, what are the things i should concentrate if i upscale the machine?

Apart from the obvious, like sturdy frame and gantry. I intend to use 100x100x4 profile and 100x100x? for the gantry.
and possibly size 30 Hiwin rolller bearing slides, instead of ball. I am planning to mount possibly an impact air hammer, so it seems i will further strengthen vertically one side of the gantry adding one more profile
For now it seems to me the limiting factor to all will be the gantry weight/strength ratio, so if i am right i could upscale until one reaches limit/weight for the given motors or strength for the chosen length/