Aaron gives you a choice for your z-axis ballnut, you can get single circuit preloaded or double circuit. He recommends the double circuit eventhough it has a backlash of around 0.002 because the forces on the z-axis can exceed the preload and cause issues.
Are these forces from the weight of the head?
If the forces are from the head weight, could we add gas springs like on this syil
in a similar way to the z-slide of the ih mill?
Then put preloaded ballnuts on the z-axis without any issues? Thanks.