Remember awhile back when I said my hot-end started having trouble holding temperature? Turns out that was probably not exactly the case.
I started a print tonight and left the printer alone in the laboratory to warm up. While I was upstairs, enough time had passed that I expected to have been hearing the whirr of the machine, but it was silent.
When I returned to the lab to see what the hold up was, smoke was pouring out of the hot-end. Before cutting the power I noticed that the realtime temperature was reporting more than 10 degrees below target (190c), but obviously the nozzle was much hotter than that
I think it’s fair to say that there’s something wrong with the thermistor, that it’s reporting bogus information back to the firmware. I’m hoping I can salvage enough from the hot end (a J-Head) to get the machine working again this weekend, but I guess we’ll see.
What my take-away from this is, given the catastrophic results of this failure, maybe it would make sense to have some redundancy in the temperature metering of the nozzle? The secondary could be something much more crude than the primary thermistor, it could even be some infrared thermometer that doesn’t have physical contact with the nozzle, just something to shut down the heater when the temperature goes wildly out of range and the primary sensor is reporting that things are normal.
On a related note, is @Josef_Prusa s new nozzle out yet (or if not, any recommendations better than the J-Head)?