Clogged hot end

Hi everyone,
The hot end of my Mendel90 is clogged. No more plastic goes out of the hot end whereas the motor and extruder mechanism are ok. For information, I use PLA.
I think this is a common issue, and that there are several methods to unclog it. But maybe some tricks should be avoided as they may damage the hot end. Can you advice for a good tutorial for unclogging the hot end ?
In addition, are there any recommandations in order to avoid such issue in the future ? Should I do regular maintenance operations on the hot end ?
Thank you.

you could take it all apart and then torch it to burn out the clog.

do you happen to have a removable tip?

Before you disassemble the hotend you should try the various "cold-pull" techniques.

The Mendel90 build manual describes one such method and whosawhatsis has also published a similar technique here.

Regards,
Neil Darlow

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I try to write with consideration for all nationalities. Please let me know if something is unclear.
Printing with Mendel90 from fedora 25 using Cura, FreeCAD, MeshLab, OpenSCAD, Skeinforge and Slic3r tools.

Yes it shouldn't be necessary to disassemble it (unless the PTFE liner is damaged or it is leaking) as you will need PTFE tape to put it together again and I have never resorted to torching.

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[www.hydraraptor.blogspot.com]

For future reference jammed PLA turns to chewing gum consistency in boiling water....

Hi everybody,

Here are some new information about my problem.

Yesterday evening without having done anything, I was able to extrude PLA again. I though that the hot end was unclogged by chance. I tried the "cold-pull" method in order to check if there was some dust inside. But I can't really tell if it was useful ot not because I did not find anything but I was able to extrude anyway...

Today I wanted to print a full part, but I am no more able to extrude...

After some investigation, I noticed that when the hot end is cold (at room temperature), the measured temperature (in Pronterface) is around 182°C ! Surprising... So I measured the resistance of the thermistor and I found around 800 Ohm (not kOhm, but Ohm). According the Epcos datasheet, I have found that at room temperature, the resistance is 100 kOhm, and that at 180°C the resistance is 0.832 kOhm. So I concluded that my thermistor is defective.

[www.epcos.com]

My guess is that the clog was not due to a dust, but to a too low temperature (due to a false measurement).

Did one of you already face such issue ? Is there anything I can check or I can do ?

Thanks.

The most likely cause is a leak of plastic has contaminated the cement holding the thermistor. Have a look under the silicone tape. You may be able to scrape the plastic off but it may have penetrated in which case the thermistor would need to be replaced.

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[www.hydraraptor.blogspot.com]

There was indeed a leak of plastic.

I have removed some of the plastic (scrubing with a screwdriver, without any chemical), but the resistance is still 800 Ohm.

I have attached pictures to this post.

Should I use aceton or other kind of chemical to clean the cement ?
Or the only solution is to change the thermistor ? In this case, what is the method ?

I have noticed that there is PLA inside the little insulation tube around the wires of the resistance heater. Is this an issue or can I leave it ?

And last but not least : I don't know where the plastic came from ? The nozzle tip (around the 0.4mm hole - not sure about the diameter) looks clean. So I am afraid that there is a leak between the metal part and the plastic part (PTFE insulator ?). In this case, I guess that changing the thermistor would be wasting money and time as the leak would still exist.

Thank you in advance.

Once the plastic has become conductive I think it is mainly carbon and I don't think there are any solvents for carbon. The only way I know of repairing it is to drill out the cement and fit a new thermistor.

I don't think it is an issue around the heater wires except it could conduct to the brass and then from the brass to the thermistor, which could damage the Melzi if the resistance was low enough.

The root problem is the leak. The only way to fix that would be to disassemble it while hot, replace the PTFE tape and reseal it.

I think we will have to replace it. J Heads should never leak but a small percentage do, so must be considered faulty at manufacture. Send me an email and confirm your address.

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[www.hydraraptor.blogspot.com]

Thanks for the explanations and the replacement.

I send you a separate mail with my address.