Update: This worked GREAT for the old, clear two-piece spools from eSun. The new injection molded black spools have a slightly larger hole. I've been using an elastic band around the print as a shim for now.
This adapter fits on the factory spool holder for the Ender 3 Pro. It centers the spool on the factory holder and allows it to rotate uniformly around its center.
This particular factory spool holder was a pain to work with because of the molded rings on either end that I suppose are intended to keep spools with a smaller inner diameter on the rod. These prevented me from just adding a 30mm ID/52mm OD cylinder like I did on my CR-10S. I would have needed to make the ID big enough to slip over the molded rings and then the center of the cylinder would still be off-center. I brainstormed a few ideas and settled on assembling the adapter in place, using a threaded nut. I'm pleased with how it turned out! Everything fits closely, but not tight.
Spools don't move laterally very much during printing, but I made the adapter about as wide as I could so that if the spool does shift, it doesn't fall off. This was much simpler than dealing with threads and nuts on both ends, "fun" as that might have been. The consequence of this decision is that it's a tight fit on the stock rod. You have to assemble the adapter on the rod and then attach the rod to the arm in reverse of how you might have done it stock. The assembly steps are:
Category: 3D Printer Accessories
The author marked this model as their own original creation. Imported from Thingiverse.