Summary

Size changeable linear bearing done in freecad.

Inner and outer radius.

6 holes change the radius accordingly.

Don't have a clue on how todo full parameterisation, but as I get better of course quality of Freecad file will get better.

Found that in PLA their is usually about 0.2mm shrinkage in overall diameter. So this needs to be accounted for.

Found that once shrinkage is accounted for, a typical freeplay of about 0.05mm in the radius is possible. Some teasing of the part to get it onto the slide is necessary (first layer and first couple of layers are slightly more squashed - just bash it onto your slide material) Once on a little friction moving it along will sand the part to a neat accuracy (hot water from a kettle can help here too))

Have fun saving time bothering to go to linear bearing stores where most place's customer service is atrocious () Just use standard hollow aluminium tubes or steal ones.