Hi Yoyo - I'm not sure what you mean by another rail upside down? Does it include a car? If its just a rail for extra stiffness that's an expensive addition, can use a steel bar. But the required size of the gantry is the same as any full sheet machine. Its about 120x120x3 mm at the moment which is very stiff for a kit machine. But when I get to the FEA I can change this. Currently I'm working on clean simple solutions for each structural loop which I think I'm close to. The gantry is also sized by the spindle.

I originally was going to spec a 48V DC ER17 600W as the top spindle size but people invloved kept talking about 1.5kW ER11 spindle so that's seems to be the area needed. But the 1.5kW is heavy so this contributes to gantry sag. Again once I get to FEA I'll resolve that question. Peter