[Edit 25/05/17]
Having just received big 2Kg spool which are 20 cm wide, I added a large version of filament guide. A long threaded rode is then needed for axis.

[Edit 11/05/16]
I made a new axis with smaller diameter that roll smoother on the arms. The file is "Spool Holder v4 - Axis.stl"

[Edit 09/16/16]
I've been requested for the sources of the thing, so I added the 123D Design source file. enjoy !

The full print is possible on a Prusa i3 MK2 with 250 210 mm heatbed. For 200200 heatbed however you will need to do multiple prints from individual stl file.

All the new files are labelled with version 3.25

[Edit 08/14/16]
In order to reduce stress on the filament when the extruder is at top Z position, I made some modification from the initial design: Longer arm and bigger hole in the filament guide, as well as a reversible montage, allowing two position with 5 mm higher or lower position. The filament guide is then higher with less angle on filament in high extruder position.
[End of edit]

Having a Prusa i3 mk2, the wide heatbed (250 mm) gave me some issue with the filament going sometime out of the spool when the extruder is on the very side, especially for new filament spool.

I then modified my initial spool holder to include a filament guide that prevent filament to be pulled from the side. In addition, I refined the initial design to make it easier to change the spool.

New version have then:

• Included filament guide, prevending the filament to slide on the side of the spool.
• easier spool change, no more screws on the side, just pull the cylinder, change spool and put it back
• automatic centering spool, due to the cylinder specific profile
• Large generic spool support, up to 140 mm wide
• Easy to print design, every parts hold on a single print on a standard 200 mm * 200 mm heatbed.
• Designed for Prusa i3 mk2, but should be used on any 6mm frame printer.

Just add a 200 mm M8 threaded pole in the cylinder and optionally use two bolt to maintain it. In case you do not have threaded rod, I added a printable axis that can be used instead (but I did not try it yet).

This is my initial design, so far the tests are good, but I will probably make some additional fine tuning later and add a version for M6 threaded pole.