Summary

Derived from http://www.thingiverse.com/thing:148454

I liked the original design but couldn't find the right metric parts locally, so I reworked the design to use imperial parts that I could get cheaply from my local hardware store. Also changed it slightly so that both cone wedges are identical.

Update: added printable mounting clips
Update: added generic mounting brackets (mounted a second spool on the shelf of my desk)

Instructions

Print 2x of part A and 1x of part B, and 2x of part C. Part A includes support structures in the model, so print it without supports. Part D is optional and just provides a cone-shaped spacer that can be used to hold the spool away from the printer frame an extra 15mm (I found it useful for some of my spools). Part E is optional mounting bracket that can be used to mount the rod to any surface that you're willing to drill a couple of bolt holes into.

You need a length of 1/4" threaded rod. I think mine is roughly one foot.

Also need 2x 1/4" hex nuts, three 1/4" threaded rod couplings (these are like really long hex nuts).

For the bearings, I used two radial bearings (these were MUCH cheaper than standard precision bearings), 3/8" inner diameter and 1 1/8" outer diameter.

To make the bearings fit the threaded rods I used a pair of steel spacers, 1/4" inner diameter and 3/8" outer diameter.

All of the parts were found at my local Ace Hardware, for around $10 total.

note: I used some loctite to hold the inner hub of the bearings to the steel spacers (be careful to not get any loctite into the bearings themselves or they'll be ruined!!). I also used some loctite on the two smaller hex nuts that hold the "fixed" cone in position (the one nearer to the printer is fixed in place, although it still spins freely on its bearing). And loctite is also used on the two couplings that are held in the mounting clips - the loctite there keeps the threaded rod from turning.

Filament Spool Holder