Hello to all, and my first post.
I have completed the structure of my machine, and experienced the same problem of looseness of the runners on the tubes.
The finished size of the prints were 39.5 mm, height spot on. To cure the looseness, I placed the runner in boiling water for about a minute (water level to the top of the splayed legs) and squeezed the legs together. Was 76 mm across and made them 74.5 mm across.
This made the bearings tight on the tube, perhaps too much so , but I will hot air heat them to ease the pressure. Maybe 75 mm wide would be a better fit. PLA plastic has some interesting properties. I have some bearings on the Z axis that do not touch, so will heat adjust the middle Z parts.
I am using 25 mm chromed steel curtain rails – has a wall thickness of 1 mm, but seem stiff enough. Maybe too much pressure of the bearings would delaminate the chrome coating. We will see.
I have basically used my RepRap printer for small parts, patterns for foundry work etc, so am impressed with the design and thinking that has gone into this CNC Machine.
Thanks for sharing it with us.