Hi Mogi - Your 20N/um is for the whole machine so you need to get a rough machine built and test the whole thing. I usually have a push pull load case in the middle of the gantry with the z down. Then you can establish what each structural "loop" compliance is. This tells you which bits to address. Once this is done you can apportion stiffness to each loop. The loops on a gantry machine are usually the Z axis, the saddle, the gantry, the columns and then the base back to a fixture. With a high rail design its from the wall bearings to the fixture. If your technical this maybe useful. Peter
please note this document states that a low mass machine is desirable and it explains why....
concrete base machine with metal workings - makes good sense to me
https://www.cnczone.com/forums/diy-c...ml#post2546148