Just thought I would quickly share what can happen if you’re not paying attention with a heavy mass spool if you’re not careful. I have all my spools on a dowel rod attached to the top of my printer enclosure and fed through an opening in the top. Never had the slightest issue with 1 kg spools, and I thought I would save a little bit of money and time changing filament by trying a 3 kg spool. It spins perfectly fine without friction, but the much heavier mass is enough to cause it to have significant strain on the extruder pulling it in to the hot end. You can see in the result where I provided strain relief by hand while watching it print. 
Bearings are not expensive and I have tried hard to get printed ones to work it’s not worth the effort IMO when you can just buy them.
I hadn’t even considered people would try to print ball bearings, lol. But yeah I definitely meant the quite cheap, actually functional ones you can buy or order.