I've been using my 3D printers a lot recently and as is the case with pretty much any tool, heavy use shows up flaws.
The spool holder that ships with the Ender models is a simple large diameter plastic tube. Which kind of works but I've realised this has a couple of problems.
The standard spool holder simply doesn't hold the 0.5Kg reels I have, the diameter is too large. More importantly there's a lot of friction that means it pulls the filament tight and I think on a couple of occasions has caused it to snap. I tried adding some shiny tape but it didn't really help.
A long time back I made a freestanding spool holder for my old Ormerod and I was using that for the 0.5Kg reels but the filament snapping is very annoying on a long print as the Enders have no filament sensor.
To fix this I spent a little time today knocking up a similar arrangement to the standalone holder for the Enders that goes in place of the tube. It's some 3D printed parts, 608-RS bearings, M8 studding and nuts. Now the spool moves completely freely and filament falls off the spool nicely rather than being pulled tight.