[Mogilogi]

Hi Mogi - A good machine has to be accurate at every point in its envelope. Each part needs to contribute to this accuracy so needs to be consistent. You have a high rail design which is a good basis for a machine, but you have the rails on three columns (2 spaces). If the gantry is halfway between the columns and does a plunge for instance this will be a springy spot and above the columns will be stiff. You need more columns or use webs or plates to support the rails. Never have rails mounted on "air". This also leads to vibration by evenly separating the columns you have created a natural amplifier for a second order vibration. Use an odd number of spaces or plates/webs under the rails.

Hi Peter, Thank you for this information, but isn't it true that there will be always some part below the rails that is in the air it be directly or the machine table, after all i can't support the rails all the way to the ground, also this rails is 30mm thick i can have it 40mm even + 20mm linear way guide above it, it's not enough for the stiffness ? about distribute the spacing unevenly it's a good idea i will take it, also there will be Rail stiffeners on both side and they will be held in place at the bottom by concrete like this image

I also think having the screw above the rail will give you some pain. I suggest you do not think about drives until you have settled the basic structure. The structure is more important than the drives. If you intend welding the base and columns, I'd counsel against that as well.

By the way I'm copying a existing machine design called "MR-1 CNC Gantry Mill" just fixing it to suite the way i can manufacture it, and at the end i will do many simulation to make sure the parts have the minimum deflection required to get the accuracy i want.