Thanx for your replay Jonathan,,
The fixed work table from steel but the gantry is movable and steel's density is 7850 Kg/cu.m compared to AL 2650 Kg/cu.m .
it's easier for me to use steel for all the body but I'm not sure if the 2N.m motors can handle it ,I didn't finish my calculations


about the kit,, I'll consult my friend ,an elec.eng. , I hope it can be tuned.
I'm short of time and money and the drivers are more expensive than the board , I can switch later to better drivers
Right now I'm in big trouble , I can't find screw lead (ACME) and slid rails in the market , that's why I didn't finish calculations , my last hope is printers' scrap .

Does anybody knows website? with international shipping? or another way? :S