Remixed with http://www.thingiverse.com/thing:10254 (spindle for Randyy's spool), and http://www.thingiverse.com/thing:11250 (one piece printable arms) to adapt it for the RepRap.
It's not very different from the original model, but I spend many hours in Sketchup tweaking it : correcting the scale in mm, getting rid of many mesh problems (face orientations and holes, especially in the hub), lower the height of the hub and the arms, join the arms in one piece like Fil did with the Randyy's ones, fuse the RotoScan's clip with the Tjhowse's spindle, organize the parts to be production friendly for a Mendel bed.
And finally present the whole in a "new thing" to make less works for the other who want to print that spool for their RepRap :)
For me it printed good, hub and spindle are maybe tight to clip at first but can spin freely after some movements, sometimes the dovetails can require a little sanding but its a really nice spool, thanks RotoScan !
(video of spinning : http://youtu.be/9SCrJz4pWRs)
As say RotoScan :
"Print out and assemble. The dovetail parts should not need any trimming except for part that lies against the build platform. Even so, if you assemble it when it is warm you may not even need to do that.
Wind the filament onto the spool. Start by threading the filament through the holes on the "U" shaped parts. Wind the filament so that it just lies gently in place. When you have finished loading the spool, cut the filament and then press the end of the filament into the built-in clips to keep it from unraveling."
Hang the spindle on the top bars of your Mendel and clip the spool (I have one spool per color and just swap-clip between them).
Alternatively you can print these double-fork http://www.thingiverse.com/thing:12273 if you want to hold two coils on the same spool.
Next : add this filament guide http://www.thingiverse.com/thing:11521 and you will be fine for the feeding :)