Like many makers, I have a lot of empty filament spools hanging around. They also happened to be the perfect size to show off some Cork Kitty models I had. I made a quick connector piece in OpenSCAD and converted two empty filament spools into a little display shelf.
Quick and easy.
I use supports just for the bottom lip (see image above) so that it would lay completely flat on the bottom roll. The top lip tapers up at a 45 degree angle and does not need supports.
I used OpenSCAD (souce code included). The outside diameter of the insert pieces is 52mm which fits inside my MakerGear and ColorFabb filament spools.
The top lip is tapered so as to not require supports. The bottom lip, however, does require supports. I found when that was tapered well, this piece was prone to wobbling. When it is completely flat, it does lay better on the bottom filament spool. It does require supports, but works much better.