Potential fix for J1 clicking and clogging

Like others, I have run into issues with the hotend getting clogged and the extruder clicking. Most recently, the problem occurred when running Matterhackers Quantum PLA, which is a dual color silk filament.

Out of curiosity, I disassembled my hotend to see what types of components were being used and what upgrade potentials were possible. To my surprise, there was almost no thermal compound compound on the cold side of the heat break. I believe the extruder is getting jammed due to heat creep.

I have since reassemble both extruders with plenty of thermal compound on the cold side of the heat break, and of course, no thermal compound on the hot side of the heat break. At least on my printer, the problem appears to be fixed. I just ran the Benchy test file in mirror mode with Matterhackers Quantum in both extruders and had zero issues. The only changes I made to the gcode were to increase the extruder temp to 225C and bed temp to 65C, as per Matterhackers recommended settings. I am sure any thermal compound will work, but I used Arctic MX-4.

The only real print quality issues in these samples are a bit of drooping in the smokestack which could be fixed by slowing the printer a bit to allow for more cooling in this area.


I’m getting ready to tear my brand new printer apart this weekend to implement the multiple fixes folks have shared here in the forums.

Would you mind sharing a photo or something (potentially using this photo?) of where you applied the thermal paste? (thanks for the photo @nnowak )

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The heat break is the thin, shiny silver piece that connects the brass heater block to the extruded aluminum heat sink.

  1. Unscrew the nozzle
  2. Loosen screws and remove the heater cartridge and thermistor from the heater block
  3. Unscrew the brass heater block from the heat break
  4. Unscrew the heat break from the extruded aluminum heat sink
  5. Apply thermal compound to the threads of the heat break on the end that enters the heat sink. Do not apply thermal compound to the end of the heat break that enters the brass heater block.
  6. Reassemble in the reverse and then hot tighten the nozzle

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You are a gentleman, and a scholar. Thanks for this!

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Alas, I just had mine apart a couple of days ago. Oh well, I have the hardened nozzle hotends coming, that will be my first step before installing and I’ll do the current ones then too.
Sincere appreciation to all you guys that know far more than I do. When I started 3D printing, I just wanted to print, had no idea I’d be re-training for a second career, or so it seems.

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UPDATE: The problem is better, but alas, not completely resolved. I was running a larger, dual color print with Matterhackers Quantum in both extruders. A few hours into the print, I started to get the clicking/clogging issue again.

One new thing I noticed is the retraction settings have a huge impact on the clogging issue with this filament. I am using Cura and one of the profiles (don’t remember which one) was using 6.5mm of retraction. This caused a lot more clogging issues than some much shorter retraction distances.

It depends of course from the filament, but with dual gear direct extruders retract can be as short as 0.8 or 1mm. I am wondering where the 6.5 was coming from - that is far from being reasonable.

It looks like the 6.5mm of retraction is what Cura has as the default for “Generic PLA”. Switching to some name brand PLA’s brings it down to a much more reasonable 1mm.

I have been having these problems too, it’s put me off using the machine as it’s hit and miss whether my long prints will succeed. There is under-extrusion before the printer detects a clog/feed issue and the print is ruined.

Interestingly I tried a calibration print with similarly high retraction values and noticed clogging and terrible print quality right away. I think you are right that this is a heat creep issue, which is exacerbated by excessive retraction of filament. This is worrying however, as I’m not sure there is a easy fix.

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For what it’s worth, I was having major issues with the right extruder when printing, with it reporting clogging every few minutes. There actually was no clog and the error message would occur just after it started making grinding noises.

I found on other posts that the grub screw for the filament feeder might be loose, which it was and after tightening it, I still had exactly the same issue.

In Cura, I changed the retraction distance to 2mm, which also made not difference, HOWEVER, when I changed the retraction retract speed from 40mm/s to 25mm/s, this seemed to solve the issue. I also decreased the maximum retraction count to 4, to ensure the filament does not experience excessive grinding. I have now been using it continously for 3 days and have so far not encountered the problem.

Ran some more prints over the weekend and did some more testing. Since adding more thermal compound to the heat break, I have had zero issues with regular PLA’s. Most of my regular PLA’s are Ingeo 3D870 based “Pro” PLA’s and they are working great with pretty much any file and varied retraction settings. For example, I modified the included 2 color shark file to print at 225C and there were no issues running PolyMaker PolyMax in one extruder and 3DFuel Pro PLA in the other.

Silk PLA’s, on the other hand, are still giving me issues. I was curious why the Benchy test file worked fine with Dual Color Silk PLA, but the Two Color Shark test file would have jams, even though temp settings were the same. I scanned through the GCode, and it looks like the Benchy file has zero retraction for most of the print, while the Shark is using 1.5mm retraction at 30mm/s.

In some cases when a clog was detected, I could just push “Load” and the clog would get forced out. Other times the clog was more severe and I would need to do an “Unload” and then a “Load”. I checked the grub screws on both extruders, and they were both properly tightened from the factory.

I am waiting on a part to fix my filament dryer, but am planning to do testing with reinforced and unreinforced Nylons later this week.

Out of curiosity: did someone try to replace the heatbreak of a hotend with such problems with another (maybe better) one, such as the MicroSwiss MK8 heatbreak if that one fits?

The heatbreak in the J1 appears to be a custom design. When I had mine apart to add thermal compound, I did a bit of searching to see if I could find anything with similar dimensions, but nothing was close. The most notable difference between the J1 heatbreak and something like an E3D V6 is the neck of the heatbreak is about double the length compared to the E3D version. The threaded portion that goes into the heatsink is also quite a bit longer than many other designs.

Okay, thank you! Let’s see how this looks like when I get mine. As far as I can judge from the few pictures you can find, I would suspect that at least the dual material heatbreaker MicroSwiss designed for the Flasforge Finder (Thermal tube for Micro Swiss All Metal Hotend Kit for Flashforge Finde — Micro Swiss Online Store) might be adapted to fit the J1.

But before that, I will probably check if some additional chamfers might help with increasing the airflow through that heat sink. From what I get from all the discussions here, there is not too much missing…

I had similar thoughts about the heatsink, or changing fans, but now I am thinking that is not the issue. I preheated both my J1 and Prusa I3 MK3 to 215C. Once up to temp for a while, I shut off both heaters at the same time. The J1 cooled off significantly faster than the Prusa. After just a couple minutes, the J1 was a good 25C cooler. The Prusa is running an E3D V6 setup with a titanium heatbreak and plated copper heater block. It is possible the lower thermal conductivity of the titanium heatbreak was slowing the cooling, but the thermal mass of the plated copper heater block should be fairly close to the brass/bronze heater block used in the J1.

That might be exactly what we are searching for: the faster the system cools down, the better the thermal conductivity between hotend and heatsink.

But on a full metal hotend, you want a high temperature gradient between hotend and heatsink to be sure that the melting zone does not creep too high - hence the thermal grease only at the upper connection of the heat break. But the better the thermal conductivity, the lower the thermal gradient.

The difference in cooldown rates could also be due to the different fans.

Prusa I3 MK3 - 4.8 cfm with a static pressure of 1.78 mmH2O
J1 - 3.79 cfm with a static pressure of 5.43 mmH20

Unobstructed, the Prusa fan will flow more air, but once you get a heatsink in the way, the J1 fan will likely move more air.

Just measured and modeled up the J1 heatbreak. After spending some time examining this heatbreak, I am 99% positive it is titanium, and not the typical stainless. The 4.1mm bore in the top of the heatbreak houses a 15mm length of PTFE tubing. Compared to an E3D V6 heatbreak, there are actually more similarities than differences.


Now this drawing is great, thanks! I wonder though that Snapmaker did not note the PTFE tube in there - I suspect the users will need to replace that one once in a while.And I would take a thorough look at the place where the PTFE hits the bottom of the hole. Such a design is prone to some burrs that might dig into the filament if your drawing is correct.

I remember from E3D that to avoid any issues they urge the users to cut these tubes very precisely rectangular and slightly longer than the space for them is, so the PTFE tube will be compressed a bit… this might be something to take a look at here as well.

Apart from that, titanium would be quite good since it does have a bad thermal conductivity which is great for the thin section of th heat break but bad for the thick portion directly above it. And it also as a high frinction coefficient against virtually everything else, so the “frying pan burn-in” procedure mentioned here probably really makes sense…

Is the whole thing coated, especially on the inside of the 2mm hole? I do not know how high the percentage of users that have issues is, but it feels to me so far that it is just a certain percentage of them. Therefore my guess would be this is not a conceptual error but rather something that originates from a not-yet-stable-enough production process, and an unreliable coating inside the heat break (which is a difficult process, both for production and quality control) might just be the thing to produce such issues, especially if I take the friction behaviour of titanium versus the one of a nickel or even a Twinclad coating into account…

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The heatbreak does not appear to be coated, but it is very finely machined with no signs of any burrs or scratches. From what I could see, the inside bore looked incredibly smooth. I am not at all concerned about coatings on the heatbreak. E3D does not coat any of their heatbreaks, including the titanium versions, and they work flawlessly in my other machines.