Lately, there have been a lot of spool holders posted on Thingiverse. I promised others on Thingiverse that I'd post this last week. It's been stress-tested for several months now and is ready for primetime.
Here is the second version of my original filament spool system with significant advantages. First, it's 100% printable. No hardware is needed for either the mount or the actual spool! The entire spool and mounting hardware can be printed on a Cupcake / ToM from only two .stl plates, and only four prints. Its standard size is ideal for 1lb rolls of plastic and has been tested with ultimaker and MBI rolls. Even if you order 5 lb rolls, unless you print constantly, you probably should cut it into smaller bundles since the hydrophilic plastic will absorb moisture.
The spool mounts to the side of the Cupcake (I don't have a ToM but expect it would work too) with friction-fit clips. A PTFE tube to act as a guide for the filament is optional but recommended (I have successfully printed about 3 lbs of plastic both with, and without, the guide tube). The spindle can be removed by squeezing the bird's mouth tabs on the end of the spindle post and pulling the hub off. The hub and filament can be placed into a plastic bag (without removing the filament) to allow it to remain dry when not printing). The hooks that hold the filament have clips that hold the tail end of your filament (to prevent the filament from tangling) and to clip the working end when it's removed for storage.
The design is almost fully parametric, so you can print different sized hubs and clips for different spool diameters and filament sizes (I've tried 3mm and 1.75mm).
I originally used bearings on the hub but found that it is TOO low of friction, causing the spool to free-run and spooling off too much plastic. Although you can use bearings, some tension is necessary. The spindle post includes code to print a spring tensioner as shown in the photos.
The stl's can be printed as is, but if you want to make parametric designs from the OpenSCAD file, also download Libs.scad from http://www.thingiverse.com/thing:6021 as it has required modules.
1- For standard 1lb. rolls of 3mm filament, just print one copy of the HubSet.stl and three copies of ArmSet.stl. For additional rolls (where the spindle post and tube guides are not needed), print one copy of Hub.stl instead of the hub set.
2- Snap extension arms and arm ends into hub.
3- Snap two of the three hooks into the arm ends and place your filament on the two hooks.
4- Wrap the third hook around the filament bundle and snap it into the third arm end.
5- Mount the completed spool onto the hub post, which I chose to attach to the left side of the bot.
6- Route the filament through the (optional) PTFE tubing or tube guides and into the extruder.
The standard stl's work well for me, but if you need different sizes, change the parameters in the scad file.