PRUSA edition heat break easily jam/clog with PLA  

Page 1 / 9
  RSS
Antimix
(@antimix)
Estimable Member

Hello,

while I was working on tuning the MMU2S, I suddenly discovered a problem that affects the i3MK3S heat break.
It seems designed in a way that facilitate the filament jams.

I spent days to analyse the issue and understand what hell was happening, but then finally I figured exactly how the whole process happens.
To explain better the issue I prepared a PDF document with detailed drawings, schemes, and photos, that you will find attached.
I preferred this solution since I have problems to do a nice document in a forum post. Study it carefully, since the problem may apply to all.
I summarize here:

HOW IT HAPPENS IN SHORT WORDS:

The problem happened for me always printing PLA, so who prints using ABS/PETG probably should not be affected, and can leave the printer as it is.

The PRUSA edition E3D V6 heat break  is different from the original, and it is built by E3D just for PRUSA. This heat break has a bottleneck inside, changing suddenly the diameter, from 2.2mm to 2.0mm, in the middle of the heat break. The filament in certain conditions become soft and may assume the 2.2 mm cylindrical shape (so it is not any more 1.75) and then is not capable to fit into the 2.0mm secondary channel to reach the nozzle, and the filament jams. Then you have under extrusion and your print fails. Note that the nozzle is not blocked, stays just empty.
The PRUSA PTFE small diameter (1.85mm or 2.0mm ) inside the cooler makes the consequences of the issue worst; see the PDF.

CONSEQUENCES:

In the worst conditions, you need to dismount all the extruder to remove the filament. In the best condition, you just unload the filament, cut the initial clog,  reload the filament, and continue to print.

WHY IT HAPPENS:

I do not know with certainly. What I verified is that several type of PLA filament, should have a wide temperature range material transition, so they become just soft far from the official melting point (print temperature).
May be that my analysis in the PDF is absolutely correct and there is nothing else to know. It is so by design.

I have done several tests, and as example if I print a support material test (around 3x3 cm) , it prints perfectly. If just later, I print something larger (say 16cm x 16cm) it starts to form the clog during the initial long infill. I think it is also influenced by a combination of gcodes, where if the material is constantly pressed, at slow speed (1st layer) for long time (where at example the infill take 20minutes), the filament flexes and forms the clog.

However:

  • PRUSA chosen to use a modified heat break with a bottleneck inside against the original that is all 2.0mm. They spent money and time to use this special version, so there should be very good reason. May be is related to the process of the ideal "perfect filament arrow head."
  • PRUSA chosen to use a PTFE tube in the MK3S cooler with a channel of 2 mm, that is 0.2 mm less than the heat break channel, and this WILL cause jams unless they are absolutely sure that the filament exit so fast and melted that will be compressed into the 2.0 mm filament. The same apply with the MMU2S modification where the PTFE diameter becomes even more smaller (1.85mm.)
  • Probably this extruder design was though with a goal of good prints of high resistance materials like PETG, ABS, Nylon and other that require 230-260° to be printed, and that do not present the issue of the softening.

 

WHAT TO DO TO MITIGATE THE ISSUE:

  1. The easiest: use good PLA filament with a short transition temperature point
  2. Switch to print only PETG or ABS or other high temperature melting point materials.
  3. Of course, if you, like me, already have 15/20 PLA spools, and you want to use them, you should invent something to be able to use them, unless you decide to drop money away.
  4. My first goal was to unify the channel diameter, so I removed the MMU PTFE 1.85 from the cooler and replaced it with another of 2.2mm
    That non solved the issue, but allowed me to unload the filament every time it jams without the need to dismount the extruder.
  5. Then I drastically lowered the PLA printing temperature moving from 215/210 to 193/189
    At this temperature seems that the heat transmitted from the heat break is not enough to soft the filament, and I was able to print the gcode area that previously failed. However it is not suitable for support. The filament is too dense and often supports are destroyed when the nozzle moves. It requires constant observation of what is happening on the plate.
  6. I also ordered an original E3D V6 heat break without the bottleneck, with the internal diameter constant at 2.0 mm. I will receive it in the incoming days.
  7. I have no idea of the impact of changing the PTFE tube diameter on the MMU2 usage. At the moment I am printing in MMU2S single mode.
  8. I will have probably to work also on the movements that forms the perfect filament arrow in PrusaSlicer , since now it does not seem very good after lowering the temperature.

- Have someone of you experienced the same issues, or you all use good quality 30-50€ PLA spool  or print PETG only?

Regards

 

Posted : 29/06/2019 8:54 pm
stephan.l6, KZONEat, heiko.ott and 2 people liked
david.a66
(@david-a66)
Honorable Member

is your printer in an enclosure or warm room?  the problem you are having is typical of printing PLA in an enclosure or very warm room . 

Posted : 29/06/2019 10:40 pm
Antimix
(@antimix)
Estimable Member
Posted by: david.a66

is your printer in an enclosure or warm room?  the problem you are having is typical of printing PLA in an enclosure or very warm room . 

Oh, probably. The printer does not have any enclosure, but I have 27° C in my room....

Posted : 29/06/2019 11:17 pm
Tim
(@tim-m30)
Illustrious Member

The heat break is the issue, not the room temperature.  I replaced the Prusa version with a stock E3D version and ALL of my jams went away. Not a single jam since I did the swap. I wasn't plagued with jams before the swap, but had serious problems with certain types of parts, having to move temps around, changes speeds, etc. And there was one part that would fail at the same point every single print. The swap allowed me to complete the part: 90+ hour print time, with so many retraction/z-lifts you get dizzy reading them all. 

 

As for it being heat related, no - not at all environmental. Here's a sample of the filament pulled after a jam. That knob at the end is 2.2 mm ... and doesn't fit into the heat break melt transition zone.

This post was modified 1 year ago by Tim
It is always wise to get more than one opinion......
Posted : 30/06/2019 1:17 am
Antimix liked
nikolai.r
(@nikolai-r)
Noble Member

3D Printing Nerd did a video in regards to the issue.

In case you're printing only single color it might make sense to change to original E3d heat break. But in case of MMU2 I wouldn't do that. There must be a reason why PR did that modification.

My solution to this problem is just to increase the temperature and print faster. After the upgrade to MK3s/MMU2s last week I'm printing all the time MMU with default settings. So far the loading issues are pretty nice handled. The filament tip is sometimes slightly bigger and if it fails to load two times, it unloads to MMU and I can just remove the filament, cut off the tip and print proceed. My room temp in southern California is also pretty high. 

The old MakerGeeks PLA filament I have in stock is also not really MMU friendly, so it's a really good test for the machine. Will report back after couple weeks of prints with suggestions. 

Often linked posts:
Going small with MMU2
Real Multi Material
My prints on Instagram...
Posted : 30/06/2019 1:36 am
Antimix
(@antimix)
Estimable Member

I already ordered an original heat break from E3D last week, and I should receive it in a couple of days.

Then I will probably install it.

I understood that is difficult to have an all-purpose printer that works well. Probably the PRUSA heat break was designed to improve the MMU filament change, with probably the goal to use it mostly with high temp filaments (like ABS or PETG).

But for sporadic MMU use, and with low temp material like PLA, probably the advantages are overcome by disadvantages, so probably the original E3D version is the best compromise.

 

Posted : 30/06/2019 5:11 pm
peter.m26
(@peter-m26)
Honorable Member

A extra fan on the extruder wil also help, or a fan to blow on the extruder.

https://www.thingiverse.com/thing:2975582

The fan on the extruder i have done, and blow air to the top.(cools the extruder very good)

And for the summer a extra fan to blow in the case, with only pla printing.(i have a enclosure and with pla only the door stays open).

Also search for how to install the tube heatbrake nozzle, search for prusa how to, and search youtube for a good manual.

This post was modified 1 year ago by peter.m26
Posted : 30/06/2019 5:20 pm
bobstro liked
sjoerd
(@sjoerd)
Active Member

I'm having the exact same issue, I've also ordered a original heatbreak to replace the prusa one. It will hopefully get here on Tuesday... I'll update this thread as well when I have the result.

I'm sure a high room temperature does not help. Here in the Netherlands we had a couple hot days where the room hit 28C and it's impossible to even print on those days. On colder days at least 3 out of 4 prints make it past the first hour or so.

Check out the fattened bits on these cold pulls 😱 

Fat ended cold pulls with prusa ridged heatbreak

This post was modified 1 year ago by sjoerd
Posted : 30/06/2019 6:23 pm
Tim
(@tim-m30)
Illustrious Member
Posted by: sjoerd

Check out the fattened bits on these cold pulls 😱 

You need to measure the stub diameter.  2.0 mm is okay, as that is the melt zone diameter.  2.2 mm is bad, as that is the heat break diameter above the melt zone. 

Posted by: nikolai

My solution to this problem is just to increase the temperature and print faster.

Nikolai - printing faster and hotter doesn't work when these jams are happening.  If fact, hotter made them worse in most cases, with the jam happening sooner.  

In theory, the 2.2 mm zone allows for filament with stringy tips to enter and push down the heat break more easily.  The stringy tip caused by removing hot filament. Users without an MMU general trim the "old tip" before loading filament.  The MMU doesn't have that option (though they have a cutter now).  When reinserting the old filament, that string folds back and creates a wedge that would jam in a 2.00 mm heat break. 

What Prusa doesn't understand is that the step from 2.2 to 2.0 mm MUST be in the melt zone for this to work.  But in a lot of cases, especially at PLA temperatures, the step is NOT in the melt zone, it is too far away from the heat.  So the stepped region can't melt plastic and it jams.  I'm fairly confident it detrimentally affects some MMU2 users, too. And the cause of many of the MMU complaints of no extrusion.

The step needs to be below the neck (the neck is the melt transition zone). 

Someday if I am curious enough, I'll drill out my old Prusa heat break, moving the step another mm down, and try it again.  And if I had an MMU, I definitely drill out the heat break before operation.  I also don't know why Prusa doesn't just drill the entire length 2.2 mm and be done with it.

 

This post was modified 1 year ago 2 times by Tim
It is always wise to get more than one opinion......
Posted : 30/06/2019 7:00 pm
sjoerd
(@sjoerd)
Active Member
Posted by: Tim
You need to measure the stub diameter.  2.0 mm is okay, as that is the melt zone diameter.  2.2 mm is bad, as that is the heat break diameter above the melt zone. 

Yep, my shitty analog callipers say more then two mm...

Posted : 30/06/2019 7:28 pm
nikolai.r
(@nikolai-r)
Noble Member
Posted by: Tim

Nikolai - printing faster and hotter doesn't work when these jams are happening.  If fact, hotter made them worse in most cases, with the jam happening sooner.  

I don't really understand the flow dynamics. But based on my experience pushing more filament over time helps to avoid it. Print from yesterday on my newly upgraded MK3s/MMU2s. Everything is still stock:

  • Layer height: 0.2
  • Nozzle: 225C
  • Default PrusaSlicer settings
  • Room temperature: 28-30C
  • No cloggs

Nozzle temp is a double sided sword. If you print with 0.1 and small things (slow speed), you most likely have a lot of retraction in addition. This leads to very slow filament flow and heat creep is a result. With R3/R4 extruder it got much better but still the printer design is prone to heat creep. In this case raising the nozzle temp will lead to exactly what you've described. But if you have high/higher filament flow than it's beneficial to raise the nozzle temp as the extruder motor has less work to do. So it operates cooler.

 

This post was modified 1 year ago 2 times by nikolai.r
Often linked posts:
Going small with MMU2
Real Multi Material
My prints on Instagram...
Posted : 30/06/2019 7:32 pm
Tim
(@tim-m30)
Illustrious Member

The factor that creates the issue - at least in cases I have experienced - is hammering or pumping of the filament. 

For example, I printed a mask that took more than a week of 24/7 printing (9 days), and had zero jams.  The mask was very simple print, larges areas of support and simple part geometry.  Perhaps 50 retractions per layer, but generally fewer.  

Then comes a part that has a lot of complexity, like a topo printed normally, lots of hills and valleys, thousands of discrete points to print, thousands of retractions and z-hops per layer.  The jam will happen within an hour.

And you can see the pumping effect in the filament stub.  Where 1.75mm filament pumps down into the melt pool and squishes out filament around the cold new filament, building the stub up in the 2.2 mm zone. After enough of these pumps, the stub is now long enough it is completely outside the melt zone, and too large to fit down the 2.0 mm neck. 

The print speed is almost fixed at minimum: printing discrete points are pushing so little actual filament volume the speed is dependent on travel speed rather than print speed. 

Increasing nozzle temp can move the melt zone higher up the neck, but melt can still cool in the 2.2 mm zone and then under-extrude or even jam when the next high flow condition begins.  

And how the hot end was assembled also plays into the problem. If the heat break is farther down into the heater block I think it will help reduce the issue. If the heat break is farther out of the heater block it will increase the issue.

But by changing the step farther down the heat break, well into the melt zone, even 2.2 mm plastic will melt when hitting the step.  We really need some thermal modeling software to show what's happening.

With the stock Prusa heat break, this model clogs every time about 3 cm up the build.  Printed successfully first try after installing the E3D-V6 standard heat break. Same gcode.

 

This post was modified 1 year ago 2 times by Tim
It is always wise to get more than one opinion......
Posted : 30/06/2019 7:49 pm
Tim
(@tim-m30)
Illustrious Member
Posted by: peter.m26

A extra fan on the extruder wil also help, or a fan to blow on the extruder.

https://www.thingiverse.com/thing:2975582

The fan on the extruder i have done, and blow air to the top.(cools the extruder very good)

And for the summer a extra fan to blow in the case, with only pla printing.(i have a enclosure and with pla only the door stays open).

Also search for how to install the tube heatbrake nozzle, search for prusa how to, and search youtube for a good manual.

Peter -- The heat break jam is totally and completely unrelated to the extruder motor temperature.

It is always wise to get more than one opinion......
Posted : 01/07/2019 9:06 pm
Tim
(@tim-m30)
Illustrious Member
Posted by: sjoerd

I'm having the exact same issue, I've also ordered a original heatbreak to replace the prusa one. It will hopefully get here on Tuesday... I'll update this thread as well when I have the result.

Check out the fattened bits on these cold pulls 😱 

The stubs need to measure 2.2 mm for it to be a heat break caused jam.  If the stubs are only 2.0 mm, that's the nominal ID of the nozzle and lower heat break, and withing the melt zone.  2.2 mm is the upper end of the heat break, in the cold zone. 

It is always wise to get more than one opinion......
Posted : 01/07/2019 9:10 pm
lindharin
(@lindharin)
Eminent Member

Hi,

I have a new printer, and didn't have any jams for the first week using the default .4mm nozzle.  When I switched to the .25 mm nozzle, the jams started happening with these exact symptoms, including the 2.2 mm clog size.  This is with the standard silver/gray PLA filament that comes with the printer.  I have a roll of Prusament PETG arriving today.  Do you think PETG will have the same issue, or will the different temperature requirements make it more or less likely to jam?  

Side question:  are there any concerns about using PETG in a .25 mm nozzle for printing miniatures?  I've been googling it and don't find too many pages talking about PETG and nozzle size issues/restrictions, so I assume it should work fine.  Just thought I'd append it here since I'm asking the main question about jamming anyway.  

Thank you all for your advice!

Posted : 03/07/2019 3:33 pm
david.a66
(@david-a66)
Honorable Member

.25 nozzles should work fine, but, if you have lots of retract moves and especially if they are longer than they need be, you can pull warm plastic up into the cold part of the extruder and cause jams.

Posted : 03/07/2019 4:27 pm
bobstro
(@bobstro)
Illustrious Member
Posted by: lindharin

[...] Side question:  are there any concerns about using PETG in a .25 mm nozzle for printing miniatures?  I've been googling it and don't find too many pages talking about PETG and nozzle size issues/restrictions, so I assume it should work fine.  Just thought I'd append it here since I'm asking the main question about jamming anyway.  

It should work, but:

  • PETG tends to be very stringy. Cleanup may be difficult.
  • PETG prints best with minimal cooling. This may make overhangs, bridges and supported appendages tricky. Insufficient cooling and they're likely to sag. Too much cooling and PETG has poor inter-layer adhesion, resulting in fragile parts.
  • PETG is much thicker than PLA. The Prusa default for the Max volumetric speed for PETG is roughly half (8mm^3/s) of what Prusa suggests for PLA (15mm^3/s). Different PETGs may require reducing this further for best results.

I have done a small amount of testing with PETG with smaller nozzles, but nothing comprehensive.

My notes and disclaimers on 3D printing and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan...
Posted : 03/07/2019 4:56 pm
nikolai.r
(@nikolai-r)
Noble Member

It does work with 0.25 and PETG but with PLA the prints looks nicer.

Often linked posts:
Going small with MMU2
Real Multi Material
My prints on Instagram...
Posted : 03/07/2019 5:31 pm
sjoerd
(@sjoerd)
Active Member

So the replacement heat break (without 2.2mm->2.0mm ridge) finally arrived today, I've installed it already. First print that failed consistently before completed just fine on the first try... Time for more printing, I'll update here a bit later with my findings.

Posted : 04/07/2019 5:33 pm
sinoth
(@sinoth)
Active Member

Thanks for everyone providing input in this thread! I believe my new MK3S is experiencing this issue. After assembling the printer I used the gray Prusa PLA to print some stuff off the SD card which worked great. I immediately switched to a spool of PushPlastic PETG and had zero issues. After finishing that spool I switched to a PushPlastic PLA and now I'm experiencing frequent clogs.

Posted by: Tim

The factor that creates the issue - at least in cases I have experienced - is hammering or pumping of the filament.

This is my experience as well. Printing simple parts such as calibration cubes works fine, but the moment I switch to a part with complicated layers (many retractions and hops) the nozzle consistently clogs. Removal of filament shows the 'squished' plug. Width of this plug is at or slight larger than 2.2mm.

My printer is in my garage which hits ambient of 35-40°C. This likely exacerbates the issue :/

I'm going to order the heatbreak mentioned above, but can anyone recommend temporary fixes until I can swap it out? If I understand correctly, the problem is the filament softening up enough to deform into a >2.2mm plug which stops the flow. Would printing at a lower temp with less retraction help, or is that only delaying the problem? Would higher temps keep the plug soft enough to push through? I'm currently printing at 210°C, but will experiment up and down a bit.

Posted : 09/07/2019 11:03 pm
Page 1 / 9
Share:

Please Login or Register