hi eddy, yes i am going for 2 bearings per rail, 4 bearings per X side, and when i ment spacing them out, earlier, its the gap between the bearings per rail, not the rails themselves ( top bottom ) .

I think that overdoing it on the bearings and rails, will allow me to make the gantry lighter, and a stable box, If i can get the gantry lighter, i dont have to worry about inertia , am also thinking that, in might want to be able temporarily add weight to the Gantry for some jobs, like surfacing stone,

I did go down the heavy road at first, and gantry weight, can cause as many problems as it solves, every time i work on the calculations with heavy gantry, am hitting performance limits on bearings, then bar, way before the machine design going to hit any problems. Then when you look at the costs of baeringfs an rails that will perform ok with the weight, ooooaaaarrr , then, when your bearings and rail can take it, your machine may need supporting. chicken and egg game.

whereas, the more rigid the Y, the less weight it needs to be stable