spool holder

i received my 3d printer recently with a spool holder that i feel can be improved even if just a little

my printer came with a filament spool that had 55mm hub, later i bought 2 hatchbox rolls that had 30mm hubs, while printing they roll on an 8mm rod.

this is my attempt to making a spool holder for both.

i tried using a bearing at first but it failed, due to the bearing not having a cage built in.
after that i designed one with a cage, however the cage was too close to the inner and o