I bought a used 600 mm diameter table for 10 € and transported it back home on the train... Ü

I designed retainer rings for the bearing balls in OpenSCAD and printed them out of PLA. I'm sure it'll be up for the job strength-wise; the component doesn't carry any significant weight, only keep the balls in place. See the diagram:

The .scad file is uploaded in case anyone else wants to build it. As always, it is fully parametric.

Since it's too big to be printed in one piece, I cut it up into identical sections and added alignment pins. I also created an alignment tool to get them in place.