Heavy duty filament spool - for mendel

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 one