Fully clogged CHT nozzle - what is the recommended way, chemical warfare or heat?  

RE: Fully clogged CHT nozzle - what is the recommended way, chemical warfare or heat?

Maybe first try heating it up a bit above PLA printing temperatures, open the extruder idler and manually try to force the filament through by using something to push the filament down.

RE:

I recently ran into this dilemma as well. What worked for me:

Remove the nozzle and hold it with something insulated (I used some pliers).

Be careful not to burn yourself:

Take a heat gun to it for a minute and heat up the whole assembly.

Find a tiny hex wrench that will just barely fit in the top end of the assembly (not the nozzle end!).

Push the wrench in, and hopefully watch filament come out the nozzle.

Once I got much of the filament out, I let the nozzle assembly cool and reinstalled it.

Then I brought the hotend up to 260, and loaded some cleaning Nylon and let it sit a couple minutes.

If you're lucky, the clog will clear itself and you can extrude out some more Nylon. If you don't get flow out of the nozzle:

Let the nozzle cool to about 120C. Then disengage the idler lever, remove the teflon tubing, and do a pull. Repeat a couple times.

RE: Fully clogged CHT nozzle - what is the recommended way, chemical warfare or heat?

OK, thanks a lot. Seems, the new nozzle design has its downsides, too

RE: Fully clogged CHT nozzle - what is the recommended way, chemical warfare or heat?

I ran into the problem of a fully clogged 0.4mm HF nozzle on the Prusa CORE One also several times now. Never had that problem on the previous Prusa Printers nor on the XL. Each previous method like cold plug, unload filament > heat to 260°C for 10 minutes, or putting a needle into the nozzle helped.

Possible root-causes:

1. I experienced that this problem happened after prints that had quite a lot of retractions. That might be a root-cause, also heard that others run into a clogged nozzle on the CO after such prints.
2. The clogging might also occur if the printer is not cooled down properly after a print i.e. if you turn-off the printer while the nozzle is not cooled down to at least 70°C. That might lead to molten filament creaping upwards  into the HF nozzle part that is not heated by the heater block itself. If that happens the molten filament further upward will never get molten again because of the not existing heater there

To proof or fix possible root-cause 2) with heat creap of filament upwards, I removed the nozzle. I realized that the clogging was in the brass section below the copper part of the nozzle. Then I heated the whole nozzle manually with a hot gun and tried to pull out any filament residue with a thin drill or by pushing filament into the HF nozzle from top down. Both methods were not successful. Also pushing filament downward towards the nozzle end did not work. 

To understand where the clog is I saw the nozzle into various slices. See the pictures attached. Very interesting is that there is a extremely hard clog in the brass that shines metallic but not in colors that I did use before (white and orange). It is very odd and I am clueless where this is coming from.

Any other experiences or ideas from the experts here what happened / where this unsolvable clog is coming from?

RE: Fully clogged CHT nozzle - what is the recommended way, chemical warfare or heat?

Wow ...

I am using .6 HF nozzles since I had that failure. And what to say .. .works as I would expect it. Never looked back to .4. Maybe those .2 mm make a difference, I don't know ...

RE: Fully clogged CHT nozzle - what is the recommended way, chemical warfare or heat?

a 2mm drill as far as it goes then cold pull.

RE: Fully clogged CHT nozzle - what is the recommended way, chemical warfare or heat?

I used the CHT nozzle once. And when I look at the problems associated with the CHT, I'm glad I got rid of it. The few minutes of time saved compared to a normal nozzle are not worth it.

RE:

There's a fast fix to this issue:  ditch your HF nozzles and replace them with regular nozzles.  

With a regular nozzle a good cold pull shows the conical shape of the nozzle ending with a cylindrical tip corresponding to the diameter (Click to expand the photo below ).  On HF nozzles cold pulls are meaningless because the filament is split into several strands and you can't see the tip of the nozzle, so you never know if the inside is really free from residues.  

RE: Fully clogged CHT nozzle - what is the recommended way, chemical warfare or heat?

I understand there is little alternative from a marketing perspective - simplicity makes for lousy narrative when printers are compared side-by-side.

Yes, I probably wouldn't buy CHT if lost or stolen but as one came with the printer in 0.4 mm, I use it when it makes sense (that is, "not MMU") without much thinking and it prints.

I'd separate heat creep topics (nozzle clogging up above the heat break) from actual CHT-specific problems. This may be unrelated so the same problem might bite again.