I notice that someone else had had the problem of prints failing because the filament was not feeding easily (http://3dprintboard.com/showthread.p...-(-please-help )

I struck this problem while printing this: http://3dprintboard.com/showthread.p...ate-*-stl-file

I realised that the hobbed bolt in the extruder is OK for feeding filament into the extruder itself, but is terribly strong when it comes to pulling filament off the spool.

My solution to this is to check how much filament is expected to be used for the print, and pulling this much off spool before starting the print.

Old Man Emu