Printed with 2 walls, 6 bottom/top shell layers, 15% gyroid infill, 0.08mm or variable layer height, 0.1mm initial layer 

But even with 1 wall it has no problem with 1 kg spools.

You need 4 frame parts and 8 roller halves (or 4 of the single part rollers-made for). 

Apply some superglue on the edge of the roller half after inserting the bearing into it and then press it together with the other half.

Should work with a 3d printed bearing too but tolerances will need to be adjusted.