My day starts in a stimulating manner
Dear members of the esteemed community, I have several questions in this regard:
I’m thinking of adding a thermal fuse straight to the heater resistor wiring. Something in the range of 250C would do (I am working with PLA only at the moment). Any reasons why it’s not advisable?
What would be a good way of removing molten PEEK from the aluminum threads? Burning it off with a lighter torch? It does smell awful when it melts.
one reason why this could happen (and it happened quickly, in a matter of 5 minutes) is a suspected thermistor failure. If I measure resistance across its contacts (in the air at +20C), sometimes it starts at 130 kOhms and keeps on rising… 140, 150, 160 etc. Other times it settles at 131.7 kOhms.
I have a J head that looks remarkably similar. It was a thermistor failure and ~5 minutes is all it takes ! Perhaps some kind of watchdog timer that is tripped if the heater is “full on” for too long. Replaced with an all metal E3D !
Marlin actually has safety features built-in for these kind of failures - all you need to do is enable them.
As long as you’re using a fuse that is rated for those temperatures, adding one sounds like a neat idea.
If you’re planning on using a torch, make sure to do it in a well-ventilated area. It is also ridiculously easy to melt aluminum with a torch, so be careful either way. And it’s probably easier to just soften the PEEK and scrape it off instead of completely carbonizing it.
@William_Frick i remember seeing a feature that basically checks if the thermistor is reporting a temperature rise when the firmware expects one and throws an error if the hotend hasn’t heated by X degrees after Y seconds.
It’s right at the top of configuration_adv.h:
//// Heating sanity check:
// This waits for the watchperiod in milliseconds whenever an M104 or M109 increases the target temperature
// If the temperature has not increased at the end of that period, the target temperature is set to zero.
// It can be reset with another M104/M109. This check is also only triggered if the target temperature and the current temperature
// differ by at least 2x WATCH_TEMP_INCREASE
//#define WATCH_TEMP_PERIOD 40000 //40 seconds
//#define WATCH_TEMP_INCREASE 10 //Heat up at least 10 degree in 20 seconds
@William_Frick i’m not sure, but i guess it could, potentially cause hiccups on really slow hotends. It really should be enabled by default, especially with such conservative default setting. @Daid_Braam and @Whosa_whatsis seem to be fairly active Marlin devs, maybe they can elaborate.
What firmware needs is an “iff I turn on heater for sixty seconds and thermistor is still not responding shut down”, and I think they actually incorporate that, but guarding against a half working thermistor is a lot harder than guarding against one that doesn’t work at all. Anything universal would basically need a couple of parameters programmed in (or empirically determined), to give a model of what the temp rise should be for a given amount of added heating. Enough of a model programmed in that you could technically do open-loop control, so you can check the deltas against the closed loop control circuit.
@William_Frick Well, 5 minutes but it was an abrupt end of a 3-hour print. I wonder whether some excessive heat has been creeping up from hot end to cold and heating it slowly until it overheated the contact point… But then, it must have been ridiculously hot to start with, as PEEK melts at what, 340C? 150 degrees hotter than the whole thing should have ever been…
@Mike_Miller unfortunately what’s left is not a piece of plastic on the hot end but rather a coat of plastic on the threads Will try to heat it up and scrape that off gently.
@Jakov_Cordina sorry to hear that. Yours a clone too? What is the measurement on the thermistor wires?
Here PEEK is nonexistent. Or very expensive. So I thought of recycling the hot end by combining with a PTFE tube. Something like that: http://www.diamondage.geekofarm.com/wp-content/uploads/2011/11/nozzles.jpg
If this design has the right to exist - it’s not that tough to reproduce. I may even whip out my nichrome and make a heater unit smaller than the J-head cube. Aaand stick a thermal fuse into it - got one already, but they are fairly large, the size of the heater element.
Will try to heat it up and scrape that off gently.