I wanted a new spool holder for my i3 MK2 that was easy and quick to load, and held the spools from the center hub area to reduce rolling resistance. After a bit of trial and error this is what I came up with.
It requires four 608 skater bearings pressed into the hub, four 5/16" nuts, and a 5/16" threaded rod. I started with a 1ft rod from the hardware store and eventually cut it down to size. That isn't required. The handle is threaded internally and should thread onto the shaft.
Print 2 center hubs, 2 uprights and a handle. I used 0.2mm layer height for everything. The bearing stop on the flanged side of the hub is tapered, so it shouldn't require any support.
Check out more pictures and details of my design on my blog: