Extruder thermistor problem and subsequent under-extrusion issues
 
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joefiorini
(@joefiorini)
Eminent Member
Extruder thermistor problem and subsequent under-extrusion issues

Posting this in part for posterity, but also to sanity check my logic...

The other night, as I often do, I left a print going when I went to bed. I always wake up excited when I do this because it's like there's going to be a present waiting for me when I get downstairs (haha).

This time, however, I came in to find that although the extruder looked like it had completed the print (it's a tall part and the z axis was most of the way to its max), the part itself was incomplete, having reached only about 10cm tall, leaving a large gap between the part and the extruder.

My first thought was that the probe had knocked off the top, it is a pretty thin model anyway, but I could not find any evidence of breakage nor broken parts around the printer. Then I looked up and saw that the filament was gone. Apparently the spool had fallen off the its holder at some point during the print.

I replaced the filament spool, reset the printer (it also had a "thermal runaway" error) and started the print again. This is when the weirdness began.

It went okay for a few minutes, then I noticed that every once in a while the extruder temp would plummet from 247 to 40 for about 20 seconds then jump back up again. In that time the extruder fan would also shut off.

Needless to say the part was looking pretty bad: layer separation & lots of places where filament wasn't sticking well. From my understanding these are clear signs of under-extrusion.

My best guess as to the problem was that when the filament spool fell off it knocked the wires coming out of the back of the extruder and somehow loosened the thermistor connection. When I checked behind the printer, that connector (the one with the red & black wire coming out with the thick blue wires) did seem a little loose, so I plugged it back in.

The temperature issues stopped immediately, thank goodness, but I still seem to be having under-extrusion problems. I'be tried the same model I mentioned before a few more times and I keep getting the same awful results. This morning I tried a model I've had success with a few times already and it behaved the same way (so I know it's not the file).

I'm guessing that when the temp was dropping and the fan died that some of the melted filament may have hardened in the PTFE tube (or the nozzle) and is causing a slight clog. I can see where that would cause less filament to be pushed out. I'm going to try a suggestion I found elsewhere on this forum to push out the clog and see if that helps.

EDIT: Adding a photo of a print that just completed of my "last known good" model

Posted : 30/11/2016 3:29 pm
PJR
 PJR
(@pjr)
Antient Member Moderator
Re: Extruder thermistor problem and subsequent under-extrusion issues

Joe

The thermistor issue is well documented here: http://help.prusa3d.com/mk2-electronics/thermal-runaway-and-temperature-drops?from_search=14089165

Now, as a result of not feeding filament while printing, it is highly likely that there is some burned plastic debris down in the hot end and at the very lease, a nozzle clean should be carried out.

Use the Ultimaker Atomic method (modified for non-bowden): https://ultimaker.com/en/resources/19510-how-to-apply-atomic-method

You should use a light-coloured filament for the clean so that you can see if any debris is pulled out. You may need to do the clean several times and you may also end up replacing hte nozzle.

Peter

Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…

Posted : 30/11/2016 7:14 pm
joefiorini
(@joefiorini)
Eminent Member
Topic starter answered:
Re: Extruder thermistor problem and subsequent under-extrusion issues

Thanks for the suggestion Peter! I did the atomic method 5 times now. It came out clean on my last 3 tries, but the prints are still coming out terribly. If I have to replace the nozzle, I might as well get the hot end out first and see if I can clean it out manually before I spend money on anything. Can I unscrew the nozzle without removing the entire carriage from the X axis?

Posted : 30/11/2016 9:08 pm
joefiorini
(@joefiorini)
Eminent Member
Topic starter answered:
Re: Extruder thermistor problem and subsequent under-extrusion issues

Never mind, just read the section in the 3D Printing Handbook on changing the nozzle. Got a couple other tips to try from there too, so I'll see if those help later tonight.

Posted : 30/11/2016 9:14 pm
joefiorini
(@joefiorini)
Eminent Member
Topic starter answered:
Re: Extruder thermistor problem and subsequent under-extrusion issues

In the process of trying to take the nozzle off, I somehow managed to blow the brown #5 fuse on the main board. Blah. Guess I'll be getting some new fuses tonight along with a wire brush for cleaning the nozzle.

On the good news side, I did manage to find my bundled acupuncture needle, so I got that into the nozzle. We'll see what helps when I get everything running again tonight.

Posted : 30/11/2016 10:08 pm
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