UPDATE: an updated and customizable version is available here: http://www.thingiverse.com/thing:731318 . The newer version makes it easier to lift out the spool holder rod, so i suggest to use that instead
The M3D printer has a built-in internal spool holder that has some limitations. I opted to simply mount the filament spools on top of the unit, above the extruder, and using the printer chassis as base.
These are brackets only. Two sets are needed, one for each side, then simply add any dowel, rod or tubing of 1/2" OD (outer diameter) to complete this thing. The horizontal top tube needs to be 6" in length, but the vertical risers can be anything that make it tall enough to clear the printer and fit your spool size.
Can fit multiple spools.