Prusa i3 MK3 (MK2S) filament runner for external spool

I'm not a fan of cantilevering a big heavy spool off the top of the printer frame, so I go outboard. This is for use with external spool holders. I recommend: https://www.thingiverse.com/thing:1471454

print 2 of these and sandwich a 608 bearing between. Insert in hex hole at top of Z axis.

Just slide filament through angled slot and get friction-free feed.

12/23/17: can get tight printing with Z > 180mm. So I added a lift piece you can stack underneath the runner. You can add thi