Flex Filament Extruder Upgrade

This is based on the design by valpap. His design worked great for me except for de-rectractions with flexible filament. The filament manged to escape the intended filament path through the groove in the bearing. I added a bead/bulge to block the groove in the bearing. Since then I didn't have any problems with flexible filament.

After printing, I drilled the filament path out with a 2 mm drill. This gives a smooth filament path. The coupling thread can be inserted without any postprocessing.