Hotend keeps jamming, I've tried just about everything  

Re: Hotend keeps jamming, I've tried just about everything

I doubt the problem is thermal paste. I have a couple of tubes, but don't ever use them.

For the Mk2 (with MMU1), I use only 0.8mm retraction; 1.2mm does seem a bit high for direct extruder.

Your problem is most likely a gap between heat break and PTFE.

You need to unscrew the heat break from the heat sink by half a turn, insert PTFE and lock in place than screw the heat break back into heat sink. Not too tight, just by hand.

Also you need the chamfer at the lower end of the PTFE and a taper at the top end (also at the bottom may help as well).

Peter

Re: Hotend keeps jamming, I've tried just about everything

Hey Peter, thanks for your suggestions.

I had to take it apart as it was still jammed from yesterday and I took some photos. Here's the top of the heatbreak with the filament still stuck inside.

Heatbreak from the other side:

The inside of the heatsink looks clean, doesn't appear as if any plastic has oozed there:

I'm already inserting the PTFE tube like you've suggested. I even have the blue lock in place just in case, so there's no chance of it moving.

And finally, the top is tapered and the bottom has a chamfer:

Granted, the bottom chamfer isn't perfect as it was cut by hand, but I doubt it could cause this much trouble. In any case, I was getting jams with the previous PTFE tube as well, which was machine chamfered, so it fit perfectly with the heatsink. I've replaced the tube with a new one just to be sure, but it didn't help.

As you can see in the first photo (looking down into the heatbreak), there's no sign that the filament melted this high up or that it buckled. You can see there's a small gap around the filament, so it doesn't appear that it has expanded from the heat either. The inner threads of the heat sink are clean, so no oozing there.

It seems like it's jammed in the middle of the heatbreak. It looks very much like heat creep - it prints fine for the first hour or so, but then the extruder starts skipping as it jams in the middle. What I can't figure out is why it would jam so high up in the heatbreak. With the fan and the heatsink doing their job, I'm under the impression that nothing should melt in the upper part of the heatbreak.

Can you gather anything more from the photos?

Re: Hotend keeps jamming, I've tried just about everything

Can you gather anything more from the photos?

🙁 Not really, sorry. It's at this point I would swap the nozzle, but you already did that. So as long as you are using *genuine* E3D nozzles and the correct (1.85mm) ID PTFE, there's not a lot else I can suggest.

I presume the extruder fan is working properly?

As I mentioned, I do have spare thermal paste, hot-ends and fans, if you are close.

Peter

Re: Hotend keeps jamming, I've tried just about everything

🙁 Not really, sorry. It's at this point I would swap the nozzle, but you already did that. So as long as you are using *genuine* E3D nozzles and the correct (1.85mm) ID PTFE, there's not a lot else I can suggest.

I presume the extruder fan is working properly?

As I mentioned, I do have spare thermal paste, hot-ends and fans, if you are close.

Peter

I was using the Olsson ruby nozzle for over a year before it jammed the first time. The new nozzle is from Prusa, so it should be a genuine E3D. The PTFE is Capricorn; they claim 1.9 +- 0.05mm.

The extruder fan is a 40mm Noctua. However, I have no way of measuring if it's pushing less air than it did when it was new. I can feel quite a bit of air if I put my hand on the hotend exhaust vent. Maybe the bearings are dirty and it's working at a lower RPM. I've tried cleaning it as much as I can with cotton buds.

When I was searching online, a few people did write about similar issues and how the paste solved it for them, so I'll try that next. I'm currently in Germany, so not really close, otherwise I'd love to exchange the paste for a beer or šnopc 😀 I really appreciate your offer though, thank you Peter.

I'll update how it goes with the paste. I'll see if I can find the stock fan somewhere and try with that as well, it certainly can't be worse.

Re: Hotend keeps jamming, I've tried just about everything

I was using the Olsson ruby nozzle for over a year before it jammed the first time. The new nozzle is from Prusa, so it should be a genuine E3D. The PTFE is Capricorn; they claim 1.9 +- 0.05mm.

The extruder fan is a 40mm Noctua. However, I have no way of measuring if it's pushing less air than it did when it was new. I can feel quite a bit of air if I put my hand on the hotend exhaust vent. Maybe the bearings are dirty and it's working at a lower RPM. I've tried cleaning it as much as I can with cotton buds.

When I was searching online, a few people did write about similar issues and how the paste solved it for them, so I'll try that next. I'm currently in Germany, so not really close, otherwise I'd love to exchange the paste for a beer or šnopc 😀 I really appreciate your offer though, thank you Peter.

I'll update how it goes with the paste. I'll see if I can find the stock fan somewhere and try with that as well, it certainly can't be worse.

🙂

Any computer shop should have stock of small packs of thermal paste. The Noctua should do the job, but testing with an original would be good.

Never liked the Ruby. Too expensive to throw away when it's "dead".

Let us know how it goes.

Peter

Re: Hotend keeps jamming, I've tried just about everything

Let us know how it goes.

Well, finally good news. It was definitely related to cooling (or lack of).

I've tried the old, stock fan and it's blowing noticeably more than the Noctua. I don't have anything to measure it with, but I'd say at least 30% more. I've also applied a generous amount of paste on the upper half of the heatbreak. With these two "upgrades", it's been printing for 5 hours now without any issues at all (it would jam within an hour before).

I didn't want to try with just the paste first, because taking the hotend apart isn't my idea of fun if it would have jammed again. The Noctua certainly wasn't putting out as much air as the stock fan though. I don't know whether that was always the case or if Noctua simply slowed down over time. My feeling is it slowed down for some reason, because I was using it for a year prior without issues. Maybe the constant heat has changed the geometry of the blades (the tip on one blade looks a bit melted) or enough dirt got into the bearings over time. The temperature drops a lot faster now after it finishes printing than it did before with the Noctua.

Thank you again Peter for your suggestions, I hope this thread will help someone in the future as well.

Re: Hotend keeps jamming, I've tried just about everything

🙂

Peter