I've been seeing occasional under-extrusion from my Ender 3. I noticed that the filament spool did not at all unwind smoothly. After changing the spool to rest on ball bearings on the table top those issues went away. However, I prefer the filament on top of the printer. So here is my take on a filament holder for the Ender 3.

Some additional non-3D printed parts are needed, in particular 4 608zz bearings and 2 axles. I used 8mm aluminum tubing, but 5/16 dowel should work too.

I also have the source files on GitHub.

I printed the frame, rollers and washers independently. The following notes on settings:

• Print frame with supports
• Print washers with brim
• Print roller halves without support

The following quantities are needed:

• Frame (Frame.stl): 1
• Roller A (Roller A.stl): 2
• Roller B (Roller B.stl): 2
• Washer (Washer.stl): 4

Additional parts (not 3D printed):

• Bearings 608zz: 4
• Axles 8mm diameter: 2