Over the last couple of months I've read in the forums about people having difficulty with the belts' teeth rubbing on the pulley flanges or fender washers and causing print quality issues. The other night I remembered that flat belts on a crowned pulley will automatically find the center of the pulley. Flanges or fender washers are completely unnecessary!I consulted my old copy of Machinery's Handbook, 24th edition, and even though it's from the early 1990's, it has a chapter on flat leather belts, how to splice them, how to design pulleys, etc. The quoted rule of thumb is for 1/8" of crown for every foot of pulley width. That would be imperceptible and probably ineffective on a pulley this size. I suspect that recommendation has to do with the geometry and strength of the leather belts.I took a guess at a 10mm radius crown for the 6mm wide GT2 belt, and it worked great on the first try. This will concentrate the belt tension in a narrow band instead of spreading it across the whole width of the belt, but I think there is more than enough strength in the belt for that.The belt doesn't track exactly on center due to the various inevitable misalignments of my printer, but it does return to to its happy spot pretty quickly when disturbed.Video demo on my MakerGear Prusa with GT2 belts: http://www.youtube.com/watch?feature=player_profilepage&v=foQmpN2twf8Files in my GitHub fork of the Prusa Mendel: https://github.com/DaleDunn/PrusaMendel/commit/f104c989a8dd936e654f2835218a9a5363458494Just print and press the bearing in, then mount as usual. Versions for 608 and 688 bearings are included. My MakerGear Prusa uses 688 bearings, so I haven't tested this with a 608. It should work just fine, but please post in the comments if you find another crown radius works better.I also haven't tried it on my Y axis because I don't want to disassemble the printer just for this.