[Solved] Filament jams each time at same point  

[Solved] Filament jams each time at same point

I could not only figure out the cause of my problems and the solution from multiple posts, so that's why I record it here for posterity, in the hope that it saves someone else endless duckduckgoing and lots of despair.

My problem was with the filament unexplicably jamming. It mostly happened around the same spot in a print, usually after printing a horizontal shell. I could easily unload the filament, and could observe the filament having been ground away by the extruder gears and also a bit squashed. That last part obviously prevented the filament from passing through the ptfe tube since if is a tight fit. I could then start a new print without any cleaning/troubleshooting, only for it to jam again at more-or-less the same point.

I did the stardard things: different filaments, drying the filament, cold pulls, replacing the ptfe tube. Nothing helped. I did have these problems in the past but not as persistent and frequent as they had gotten now. I changed nothing to my setup and print profiles, so why suddenly? Btw I have a Revo Six hotend, but that should not have a bearing on this issue.

Until I read something about extruder temperature and how the heat from the extruder stepper can be transferred to the filament through the shaft and gear. I noticed that my extruder stepper was too hot to touch. I added an enclosure last year but that was in the fall. The attic where my printer is located can easily get above 30° in summer and, combined with the enclosure, that proved fatal. In winter the attic is below 15°, so that's why I had been printing happily and without sorrows for the past months.

To test my hypothesis,  I wanted to stick a heatsink to the extruder stepper. Until I discovered a secret setting called 'StealthChop'.

The 'StealthChop' setting was added in firmware version 3.10.0: https://github.com/prusa3d/Prusa-Firmware/releases/tag/v3.10.0

Scaling extruder motor current based on speed

The developers have discovered that using StealthChop without the “current feedback” feature of the TMC2130 has a positive effect on the extruder motor temperature. Multiple tests on our farm have shown that the temperature can be lowered by up to 10° C.

WARNING: This feature was tested only for the motors provided by Prusa Research. We cannot guarantee that this current amplification can be applied to other 3rd party motors as they might get damaged due to a current spike. For this very reason, the feature is disabled for all printers and has to be manually enabled at the user's risk.

To enable this feature, enter the experimental menu. Go to LCD menu -> Settings -> HW Setup, then scroll to any menu item and hold the knob for 2-3 seconds. After a “click” sound, the display will flash once and the “experimental menu” will appear as the last item in the list. Open the experimental menu, then select the "E-cool mode" and switch it to "ON".

I did measurements with an infrared thermometer and the 'up to 10°' is certainly not exaggerated. The extruder temp dropped from 52° to 42° and the jams were a thing of the past.