PLA Jamming happens in any all metal hotend, even with E3D, Prusa Nozzle, Printrbot Metal Hotend, etc,. PLA jamming in all metal hot end is common issue, but this does not happen with PEEK based JHead Hotends. Metal Hotend can print High temperatures filaments without any problem, this includes high temperature filaments like ABS, Nylon, Ninja Flex, etc., Here we try to list down the most command reason for jamming and solutions for the same.
Major reasons for PLA Jamming are sharp heat break, Filament retraction, Active cooling and filament quality. let see them details
Is the fan running constantly over the radiator fins? They need to be kept actively cooled 100% of the time. (a broken or miswired fan is a guaranteed clog with PLA.)
The rule is never turn ON metal hotends without cooling fan running.
The magic of the hot end is to melt the plastic just as it leaves the tip. Unfortunately, the reality is the hot end carries some heat up in the tube, melting and softening the PLA as it climbs. The soft PLA is not as stiff, and tends to bulge out as more is pushed into the end. Eventually the tube is warm enough, and the bulge big enough that the PLA jams against the side walls and prevents more from being fed in.
Minimize or Disable Retraction
Retraction is the important cause of PLA jamming on the metal hotend, so better keep retraction low as possible (<= 0.3mm)
Also try doing some test prints with 0.0 retraction, to find and make sure the jamming is not due to retraction. If your filament is smoothly when retraction is 0.0, then the jamming is due to retraction.
Seasoning the internal surfaces of the hot end with cooking oil. This might sound crazy but, it work first hand. PLA is a sugar and molten sugars stick to bare metal like stainless steel, in the kitchen you prevent this by creating an oily patina on the metal surface by baking a thin layer of oil onto the surface. There’s some science to this but we won’t go into it here. Simply dip the end of a piece of PLA (10mm or so) in canola oil or similar cooking oil, heat the hot end to about 180 degrees and insert the oily PLA into the hot end, press it through with you fingers until it exits the nozzle then extract the oily PLA, then push 50mm of un-oiled PLA through. Repeat this as many times as you like, I had success just doing it once. The hot end will fizz and pop while you are doing this as you are effectively frying the PLA, it may smell like cooking donuts This is why you need to push an unoiled piece through to purge any excess oil.
Other Common Reasons
Checkout the guide on COMMON KNOW REASON WHY ANY TYPE OF FILAMENT JAMS
If your nozzle is clogged, Try this guide to CLEANING CLOGGED NOZZLE
More online resources