Filament jams in heatbreak.  

Re: Filament jams in heatbreak.

The MMU system came with a modified heat break which was then also included in later Mk2 and all Mk3 printers.

This modified heat break has a slightly larger diameter at the top end and can contribute to this issue.

Capricorn tubing has no benefits in the hot end (it's smaller ID will add to the problem).

Best thing to do is to unload the filament immediately after a print and to ensure that the PTFE tubing has a decent taper in the lower end (as well as a chamfer).

Peter

Re: Filament jams in heatbreak.

The MMU system came with a modified heat break which was then also included in later Mk2 and all Mk3 printers.

This modified heat break has a slightly larger diameter at the top end and can contribute to this issue.

Capricorn tubing has no benefits in the hot end (it's smaller ID will add to the problem).

Best thing to do is to unload the filament immediately after a print and to ensure that the PTFE tubing has a decent taper in the lower end (as well as a chamfer).

Peter

Thanks Peter

So the Capricorn basically only makes a difference if I choose to do a bowden setup?

Excuse my ignorance, but what purpose does the tapering of the PTFE serve? I would be worried that the reduced width would make the tube wriggle when loading filament - thereby increasing the risk of the filament tip catching the the top of the heat break.

Sorry if this is a derailing of the thread.

Niels

Re: Filament jams in heatbreak.

So the Capricorn basically only makes a difference if I choose to do a bowden setup?

To be honest, I have the MMU with 1 Capricorn and 3 regular Bowdens. There is absolutely no difference between them (LA/Preload factors are the same).

but what purpose does the tapering of the PTFE serve?

The PTFE tube should be tapered at top and bottom and chamfered at the bottom. When retracting hot filament, the lower taper helps shape the filament tip into one which can pass through the whole tube. The upper heat break diameter is 2.1mm (from memory); the PTFE is around 2mm. If there's a step (i.e. no taper) then the tip of the filament can be detached and block the lower end of the PTFE tubing.

Peter

Re: Filament jams in heatbreak.

The PTFE tube should be tapered at top and bottom and chamfered at the bottom. When retracting hot filament, the lower taper helps shape the filament tip into one which can pass through the whole tube. The upper heat break diameter is 2.1mm (from memory); the PTFE is around 2mm. If there's a step (i.e. no taper) then the tip of the filament can be detached and block the lower end of the PTFE tubing.

Haha! It all makes sense. You are a champ.

Tapering the insides of the tubes in both ends and a light chamfer at the botton - got it!

I hadn't thought about the retracting issue at all - that could explain some of the later issues I had after replacing the the PTFE.
I think a lot of my confusion comes from the meaning of the word "tapering" as that can mean thining the outside of a tube as well.
That made me mistake tapering for chamfering... silly really 🙂

Thanks again

Re: Filament jams in heatbreak.

Pleasure to be of assistance 🙂

Peter

Taper tool: https://www.ebay.co.uk/itm/RC-CAR-BODY-SHELL-HOLE-REAMER-0-14mm-UK-SELLER-FREE-POSTAGE/123103493648?hash=item1ca98a3e10:g:9wMAAOSw4GVYPthQ

I use a craft knife for chamfering (chamfer first, then taper)

Re: Filament jams in heatbreak.

My new "Micro Swiss" heatbreak has fixed the issue.
LINK

Has fixed all my issues.

Watching it print at the "problem layer" I can see exactly what is causing the jam, and why it was a "wall".

It printed a "stright" infill line, that was approx 0.1 wide. (maybe narrower)

It printed this line "SLOW".

As far as the extruder is concered, that may as well be "a 5 minute pause in the print".

My new heatbreak is NOT having ANY issues.

I personally think I'm getting smoother extrusion with it as well. (Yeah, that's a head scratcher isn't it?)

My take away from this is.

E3D makes VERY high quality parts.

Micro Swiss, makes HIGHER quality parts. (The machining is BEAUTIFUL, better than even the E3D)

I'll edit this post in an hour or so, with a photo of the finished boat. 🙂

I'm also having a problem with my MK3 with symptoms like you described. Took apart my original hotend and broke the heatbreak while troubleshooting, and ended up buying a new hotend. I'm still having signs of the same problem.

It seems like this problem is quite common? Even Joe from 3D printing nerd had also faced the same problem.

I'm feeling tempted to get a new heatbreak to see if it fixes anything. Did you also apply some anti-seize when installing the heatbreak?

Re: Filament jams in heatbreak.

Capricorn tubing has no benefits in the hot end (it's smaller ID will add to the problem).
Peter

Actually it will either do nothing, or help.
The bowden tubes Prusa uses are 1.9mmID.

So if there is actually a lubricity benefit to the Capricorn, it would be better. Possibly, the best would be "el-cheapo" 2.0mm ID bowden tubes though?

I only got the capricorn becuase I was 100% out of ideas when I ordered it.

Things the filament touches as it feeds.

1. Bowden above filament sensor.
2. Bondtech gears.
3. Bowden below gears.
4. Heatbreak.
5. Nozzle.

1 and 2, were easily ruled out given where it was jamming.
5, was ruled out by replacing the nozzle with a brand new 6mm nozzle.

So I went on a limb, and thought "I wonder if this el-cheapo bowden I replaced the OEM one with, is causing the issue? (I mangled my OEM bowden up quite bad and replaced it long long before this problem) So that piece of bowden just seemed the most "logical" problem, that somehow, it was causing a problem? (After all the research I've done, I can now tell with certainty, without even needing to look... "How could the bowden prevent FORWARD feed."

So I ruled out 3. And that left me with #4.

I have been printing a Snappy mk3, for the last week and a half. (I've got about 2kg of filament in it already) and have another 1.5kg to go in it.
The only issue I've had, is the Y axis detecting a crash. During travel, at a VERY certain spot, so once I get snappy done printing, I'm gonna rebuild my Y. But I have had ZERO extruder issues in the ~200 hours I've done.

I'm also having a problem with my MK3 with symptoms like you described. Took apart my original hotend and broke the heatbreak while troubleshooting, and ended up buying a new hotend. I'm still having signs of the same problem.

It seems like this problem is quite common? Even Joe from 3D printing nerd had also faced the same problem.

I'm feeling tempted to get a new heatbreak to see if it fixes anything. Did you also apply some anti-seize when installing the heatbreak?

At the top of the heatbreak, you should apply some thermal paste.

Yeah, I agree, this issue is more widespread than I think anyone is giving it credit for.

Re: Filament jams in heatbreak.

All the Bowden tubes on my Mk2 MMUs from PR are 2.0mm ID. The PTFE tubing within the extruder cold end on the MMUs is 1.9mm ID, but that was when new; more likely to be 2.1mm by now...

The PTFE tubing on my Mk3 below the motor is 2.0mm ID.

Peter

Re: Filament jams in heatbreak.

All the Bowden tubes on my Mk2 MMUs from PR are 2.0mm ID. The PTFE tubing within the extruder cold end on the MMUs is 1.9mm ID, but that was when new; more likely to be 2.1mm by now...

The PTFE tubing on my Mk3 below the motor is 2.0mm ID.

Peter

My understanding is that the PTFE on the MMU, and I assumed it was the same on the mk3, is that the "hotend" PTFE tube, was 1.9mm, to reduce the size of the blob on the filament when extracting. It's a good idea, and why I wanted Capricorn in mine. I'm going to replace all my PTFE in my Skeletruder, when I do my next rebuild, given I think what's in it now is in "rough" shape, given I've pulled 2.3mm blobs through it.

I run a custom firmware that when retracing the firmware, it goes "very" slow in the PTFE tube, so that the "blob" cools and hardens before it leaves the 1.9mm PTFE tube. That way it passes the Bondtech gears easier, and extracts through the "top" PTFE tube easier.

Maybe Prusa changed this for some reason?

This is the best image I have seen regarding what I have "seen" in the heat break.

Notice the filament gets a "blob" or "plug" at the end of it in this image. Notice the the "white" on either side of the filament "plug" on the top half of the heat break (ABOVE the neck). The "step" from the "wider" 2mm area below the PTFE tube (above the neck) and it then "steps" down to 1.9mm, the rest of the way to the nozzle.

This "step" from 2mm to 1.9mm is where my heat-break was jamming. As it ABOVE the "neck" it is MUCH cooler at this "step", and the filament can get hard. This is what caused my "jam".

If the "step" was at the BOTTOM of the neck, it would NOT cause issues, as the "step" would be hot enough to melt the filament.

A "cold" forward "step" can "catch" your filament, and not let go. If the step was HOT... the issue would not be relevant, as it would just melt the filament to shape.

I've attached 2 images I modified to show the ID measurements, and temps.

The issue happens at the "warm temp" point. From thermal images I've seen, I would assume it's over 100c cooler than the melt temp.

The "step" should be the "higher" melting temp.

EDIT: Image taken from http://www.sublimelayers.com/2017/06/first-week-with-prusa-mm-quad-extrusion.html

Re: Filament jams in heatbreak.

I am having this issue on my MK3.... I currently have a clog in the PTFE tube just below the filament extruder pulleys after about 24 hours of actual print time. Has this been confirmed as an issue with the heat break as the OP suggested? ...and... how exactly does one go about clearing a clog there? haven't found an article on this specific clog clearing method yet....

Re: Filament jams in heatbreak.

Hi ashley.h3,

I cleaned a similar clog. Mine was a bit further down so maybe a bit easier but you could try removing the heatbreak entirely (see assembly instructions and execute them in reverse order):
http://manual.prusa3d.com/Guide/5.+E-axis+assembly/510

Once you have the heatbreak removed you can push the ptfe tube down through the tube and clean it (I just pushed the clog with a little allen).

Then reasemble.

To reasemble have the E3D-V6 assembly instructions in mind:
https://wiki.e3d-online.com/E3D-v6_Assembly

I have to do it twice because I did not screw tight the things in order so read those carefully.

Good look with the clog!

Re: Filament jams in heatbreak.

My understanding is that the PTFE on the MMU, and I assumed it was the same on the mk3

Sean

The MMU extruder PTFE was specially sourced (from Festo) at a much higher price thatn "regular" PTFE for the Mk2 MMU.

The heat break (and incidentally your dimensional image is incorrect) was modified for the MMU and then included in the later Mk2 and the Mk3.

The heat break, manufactured by E3D, is drilled from both ends with a 2mm hole. Unfortunately, where the 2 holes meet is not so precise and there was a step between the two holes on the majority of heat breaks.

This step did not majorly affect single filament usage, but it could cause a tool change to fail, so the heat break was modified and the upper hole was drilled to 2.1mm.

I was very fortunate in that my original heat breaks were both burnished (by me... accidentally, when removing blockages) and any step was not noticeable.

Anyway, for consistency, the modified heat break is now included in all shipped printers, but not the 1.9mm ID PTFE.

Initially, with the MMU, regular PTFE was used and the primary source of tip forming was the cooling tubes. However there were issues with this and the cooling tubes were increased to 1.95mm ID and the PTFE reduced to 1.9mm ID, meaning that the primary source of tip forming became the PTFE.

It really is better to get the hot tip into the cooling tubes as quickly as possible, but the downside if this is wear on the PTFE, increasing its ID.

You may also be aware that I have written and published a post-processor for the MMU which works with KISS 😉

Peter

Re: Filament jams in heatbreak.

Sean
The heat break (and incidentally your dimensional image is incorrect) was modified for the MMU and then included in the later Mk2 and the Mk3.

The heat break, manufactured by E3D, is drilled from both ends with a 2mm hole. Unfortunately, where the 2 holes meet is not so precise and there was a step between the two holes on the majority of heat breaks.

This step did not majorly affect single filament usage, but it could cause a tool change to fail, so the heat break was modified and the upper hole was drilled to 2.1mm.
Peter

Thanks for the writeup. 🙂 There's oddly not a lot in "once place" about this. This also explains why many people are having issues, and many are not.

Although I could swear there's 2 seperate IDs in my E3D Heatbreak. There is a "step" visible ONLY from the top. I can not "probe" or "see" the step from the bottom. I can both see, and probe the step from the top. I am thinking of taking it to the guys @ E3D and seeing if they can use their testing equipment to see if there's any problems with it. I can NOT identify a single problem with it.

Re: Filament jams in heatbreak.

Thanks for the writeup. 🙂 There's oddly not a lot in "once place" about this

Actually I wrote a whole load about this is one single thread (Blockage Troubleshooting) in the MMU section. Seems to be relevant to the Mk3 as well!

It's easy to burnish the inside of the heat break. Use a 1.8mm drill bit in a battery powered drill. Insert the bit into the heat break, start the drill (slowly and carefully) and use the drill bit flutes to polish the inside of the heat break.

Just be exceedingly careful. It doesn't take much, about 30 seconds of polishing at fairly slow speed. Then make sure the PTFE tube is both chamfered and tapered at the lower end and tapered at the top. Then amend you "End G-code" to unload immediately after the print. No more jams...

Peter

Re: Filament jams in heatbreak.

I borrowed sean.h8 picture from page 3(i hope you don't mind)...

Wouldn't be better to have diameters in heatbreak other way so the heatbreak shape filament to 1.9mm diameter and not a teflon tube..

Re: Filament jams in heatbreak.

Hi everyone,

I am new to this forum so first of all greetings from Germany 🙂

I am experiencing similar problems as all of you have albeit mine being limited to PLA printing only. I just recently got the MK2.5 upgrade and I have my own theories about the matter, I hope some of you can chime in and discuss these a bit:

I used to have no issues printing PLA on my MK2S, then I built an enclosure and sure enough: jams with PLA were inevitable. Back then I found out that leaving the enclosure open solved my issue 100% hence at that time it was definitely a matter of insufficient cooling above the heat break.

Then I upgraded to the MK2.5, back were the PLA jams and first I tought my jams had the same origin, no such luck....

I then ran the newly implemented PID-tuning function in the 3.1.4 firmware, which improved my results but still often caused jams. This led me to believe that maybe the new part cooling fan nozzle might cool the extruder thermistor too much (stories of thermal runaway in the past with the Prusa i3 also led me to this assumption). A result of this might be that the PID-logic might have to crank the power output up significantly to counter that.

After that I tested various part cooling fan speeds and finsished most prints at a sweetspot of around 70% speed. But still the failing prints happend at lower AND higher fan speeds... and slower print speeds...

Assuming that these blobs appear because the PLA filament is too soft at the top, my next idea was that maybe the new noctua fan is the culprit here. Sure enough it seems to perform less well at cooling compared to the previous fan. My theory is backed by the fact that the noctua is rpm regulated dependent on the extruder temperature i.e. it could have the aforementioned sweetspot by pure luck so that at slower temps the cooling by the noctua is be even less and therefore again blobs might form.

I then found Joel's video about this issue with the Robo R2 printer (with enclosure mind you) which is pretty bang on to our problems. It can be found through this link:

He basically alleviated his problem by allowing the air over the cooling fins of the extruder to flow more freely i.e. to get the heat out of there better 🙂 he also mentioned this problem maybe being connected to retraction settings.

Next step for me was to look into linear advance to reduce the need for retraction, but as it appears to still be disabled in firmware 3.1.4 I think I'll have to wait 🙂

So my best guess is that the noctua fan - while being way less annoying than the MK2S one - isn't capable of cooling well enough.

I also might want to add that I also tried printing PETG and ABS and both worked fabulously, the ABS prints even improved in comparison to before...
As both are higher temp materials than PLA this might further back my theory.

Thanks for reading and I hope to get some thoughts 🙂

Regards
DerBierBaron

Re: Filament jams in heatbreak.

Hi everyone,

I am new to this forum so first of all greetings from Germany 🙂

I am experiencing similar problems as all of you have albeit mine being limited to PLA printing only. I just recently got the MK2.5 upgrade and I have my own theories about the matter, I hope some of you can chime in and discuss these a bit:

I used to have no issues printing PLA on my MK2S, then I built an enclosure and sure enough: jams with PLA were inevitable. Back then I found out that leaving the enclosure open solved my issue 100% hence at that time it was definitely a matter of insufficient cooling above the heat break.

Then I upgraded to the MK2.5, back were the PLA jams and first I tought my jams had the same origin, no such luck....

I then ran the newly implemented PID-tuning function in the 3.1.4 firmware, which improved my results but still often caused jams. This led me to believe that maybe the new part cooling fan nozzle might cool the extruder thermistor too much (stories of thermal runaway in the past with the Prusa i3 also led me to this assumption). A result of this might be that the PID-logic might have to crank the power output up significantly to counter that.

After that I tested various part cooling fan speeds and finsished most prints at a sweetspot of around 70% speed. But still the failing prints happend at lower AND higher fan speeds... and slower print speeds...

Assuming that these blobs appear because the PLA filament is too soft at the top, my next idea was that maybe the new noctua fan is the culprit here. Sure enough it seems to perform less well at cooling compared to the previous fan. My theory is backed by the fact that the noctua is rpm regulated dependent on the extruder temperature i.e. it could have the aforementioned sweetspot by pure luck so that at slower temps the cooling by the noctua is be even less and therefore again blobs might form.

I then found Joel's video about this issue with the Robo R2 printer (with enclosure mind you) which is pretty bang on to our problems. It can be found through this link:

He basically alleviated his problem by allowing the air over the cooling fins of the extruder to flow more freely i.e. to get the heat out of there better 🙂 he also mentioned this problem maybe being connected to retraction settings.

Next step for me was to look into linear advance to reduce the need for retraction, but as it appears to still be disabled in firmware 3.1.4 I think I'll have to wait 🙂

So my best guess is that the noctua fan - while being way less annoying than the MK2S one - isn't capable of cooling well enough.

I also might want to add that I also tried printing PETG and ABS and both worked fabulously, the ABS prints even improved in comparison to before...
As both are higher temp materials than PLA this might further back my theory.

Thanks for reading and I hope to get some thoughts 🙂

Regards
DerBierBaron

Joel's problems in the models are very similar to mine. The problem with the heat creep could be the heatbreak, fan or both?

Re: Filament jams in heatbreak.

Here's what the formed end looks like for me after switching to the Micro Swiss heat break:

Much better.

Re: Heat Break disease.

Actually more like Heat break congenital deformity.( I was a doc)
I posted on April 23 "Calibration failure". If you glance at the first and last posts you will see that I had a clog, and responded by replacing the nozzle and PTFE tube. I then could not calibrate XYZ , with an error message not actually documented on the site. After a week ( no help from Prusa) some movement made had the problem go away. It makes me nervous about recalibrating. The reason for this post is that the next 7 (!) attempts to print the same STL at differing layer heights, speeds and temps, have all failed before finishing. I could always pull the filament out, and finally I recognised the little oversized cylindrical blob as being the problem documented so well in this thread, as well as the one "Filament continuously clogging."
I shall ask Prusa for a new heat break, or entire hot end, but they may well be able to outwait me. So my question is which way should I proceed. I see the choices as
1. Just buy replacement heat break from Prusa or Filastruder ( the US E3d stockists, good people). I could buy the modified one for the Mk3
2. or try to revert to the one where the PTFE goes all the way through.
3. I could buy the Swiss heatbreak.
4.I could just buy a whole new hot end.
5. Any other?
I am interested in the advice of this group. ❓

Re: Filament jams in heatbreak.

I'd get just the Micro Swiss heat break. The rest of the hardware is likely totally fine.