I tried one original and two chinese E3D v6 hotends, also original Volcano hotend with 0.6mm nozzle. All of them have the same symptom – plastic gets stuck after a while (from several minutes to hours) producing a jam inside the hotend. My printer has a Bowden 3mm extruder and a heated bed (70°C for PLA). I tried unsuccessfully (without stable result): Powering hotend fan from 16V instead of 12V. Hotend radiator is slightly warm to touch. Putting extremely powerful motor in the extruder (6.5kg·cm). Oiling the plastic. Various printing temperatures and speeds. Various PLA filaments. Is all-metal design defective for printing PLA? Are there any other options I may try? Are there good hotends guaranteed to print PLA? I made an experiment – I drilled a hole inside the hotend as shown in red on the picture: And filled the hole with a piece of Teflon tube. I’m able to print with this hotend at speeds <30mm/s, but this is not what I want.