How Would You Upgrade An Old Ox CNC Build Into A Serious Machine?

[Kitwn]

For a Z axis the larger rails can even be an advantage. Increases the plate spacing for a typical Z axis design which makes it easier to fit the ballscrew and nut between the plates. Even then, I had to machine some recesses for the ballnut on my own machine. Extra stiffness was a bonus! Depends on your Z design, of course, but worth thinking about.

I'm not sure I'd want the 15mm miniature version on any router machine. A laser cutter, 3D printer or plasma maybe but not something with cutting forces to resist. Not with the full size version costing the same anyway.

I can see the advantage of using 20mm or larger on the Z to increase the plate spacing. By sheer luck my own 20mm fully supported round rails and 1610 ballscrews fit perfectly between two flat plates which makes things easier. Not that I'm using that as a reason to recommend round rails!