Did a few more experiments with the QU-BD extruder tonight and came to the conclusion that the temperature being reported by the thermistor is probably incorrect.
I thought more about what the filament looked like when I pulled it out of the jam, and it wasn’t even hot to the touch, so tonight I reviewed my thermistor table settings in the firmware to make sure I was using the correct settings.
Turns out I am, or at least ones that are close according to this post on the QU-BD forum (interestingly enough started by me, and the first post to their forum…). Of course I couldn’t just grab the actual table from the manufacturer because they posted it as a PDF…so I’ll have to dissect that on another machine (my Linux lab workstation doesn’t do PDF).
I’m going to give the manufacturer’s table a try, but I don’t have great expectations. Out of curiosity (i.e., rage) I cranked the heat up to an indicated 260C and I was finally starting to smell melting PLA and pull (jammed) filament out that was starting to melt. I would have went further but since I have to disassemble the extruder to reload it after a jam, I ran out of time waiting for it to cool-down enough to take it apart.
I’m going to ask the QU-BD folks what the resistance should be at room temp as well, because I have a feeling this thermistor is completely off the chart.