top mounted ballscrew, would it work properly ?

[Rory13]

Hello, i am in the process of building my first cnc. I ve looked through many designs but cant really decide. The working area i m interested is 75x50cm. Mostly it would deal with wood but it could be nice if it could be design proof for metals with a spindle upgrade and some additional gantry supports in the future. The frame would be made of 3mm thick steel tube, 80x40mm in the long side(positioned vertically as pictured) and 40x40mm on the rest. The moving gantry would probably need to be from aluminium which is very expensive in comparison to steel, but i m hoping with aluminium and some steel angles where it matters the weight will stay under 30kg for the gantry including spindle, so i can get away with nema23 motor 270ozin. Where can i find some info on friction coefficients and weigh load capacity of sbr type rails ? Not even the manufacturers publish these.I suppose sbr16 supported would be fine for the long axis and sbr12 on the others. Is the ballscrew on the top of the gantry idea completely wrong ? Shall i redesign with the screw underneath ? I want to get away with a single ballscrew design to keep the cost reasonable. Initially i will just mount a dremel for tests and get something stronger like 1,5kw after my cad skills get better. Please share your opinions . Thanks.