A filament spool holder that uses garage door rollers as the ball bearings.
Remixed from http://www.thingiverse.com/thing:97734 with the Brackets_fixed.stl, and Leftupright_fixed.stl files included here taken from that thing (but run through netfabb cloud to repair them). I cut them up and modify them in the openscad files.
The spoolmount.scad file is where everything is defined. All the other scad files include it and just print one part.
This also uses the http://www.thingiverse.com/thing:116872 tension nut to hold everything on the PVC pipe.
Get two short stem garage door rollers at your local garage door business (there is usually one nearby, which is the main reason I decided on this design). You probably want to put a little light oil on them to break up the heavy grease they are usually packed with and make them a little easier to turn.
You'll need to print two of the mountingblock parts to glue to the tops of the left and right supports. I don't know how standardized garage door rollers are, but the ones I got with a nylon shell on the roller sit in these perfectly.
Print four of the innerspacer parts and epoxy two to each roller stem so they'll sit in the center of a PVC pipe. (Before epoxy, it is probably a good idea to check that they fit so the rollers can slide in and out of the pipe easily since you need to slide out the roller to change the filament spool).
Print two of the spoolsleeve parts. These are the "step pyramid" cones that fit in the holes in a reel of filament and center the reel on the PVC pipe. The part included here contains steps to fit in Octave and Solidoodle brand reels. You can fiddle with the openscad files to design different shapes to fit other brands of filament spools.
Download and print two of these things: http://www.thingiverse.com/thing:116872 (Tension Nut for 3/4 inch PVC Pipe). They are used to hold the filament spool with the spoolsleeves in the center of the PVC pipe and make sure the whole thing doesn't fall apart and jam.
Print one leftsupport and one rightsupport. These were tricky for me. They wanted to curl up. You might want to modify the design to add some holes or slots to the platform on the top of the support as that was where the curling always started for me. I eventually used ABS slurry on the bed to hold the part down.
Glue a mountingblock to the top of each support (I used acetone with a little ABS dissolved in it as glue).
Print two innerbracket parts and two outerbracket parts. These screw to either side of the support to hold the supports on the top of the printer. I found that a 6-32 tap I had would cut nice threads in the supports and with a little drilling I could fit short 6-32 bolts through the holes in the brackets for a nice solid fit.
Get some 3/4 inch PVC pipe which will hold the spool of filament and rotate on the garage door rollers. Make it long enough to fit conveniently across the printer, somewhere around 9 or 10 inches. Once the supports are mounted, you can determine a good length to use. You don't want it scraping on the supports as it turns, but you want it long enough to get both garage door rollers solidly inside the pipe.
Now you can put it all together. Shove a tension nut down near the far end of the pipe, follow that with a spoolsleeve, follow that with the filament spool (making sure to get the spoolsleeve inserted in the hole in the filament spool), then another spoolsleeve for the near spool hole, and another tension nut to hold everything in place. Slide the rollers into the pipe, and drop the rollers into the mountingblocks at the top of the supports, and you are done.
The only thing to do is decide if you want the filament coming off the spool on the front side and directly down into the print head, or if you want to run it the other way and wrap it around through the hole in the back of the printer. The first way makes covering the printer harder, but reduces filament friction to near zero. The second way allows a fairly flat cover to go on the top of the case, but drags the filament around through holes and bends and makes the extruder motor work harder.