Help! Extruder won't jam. Not having problems with heatbreak. Mk3 is too reliable.  

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bobstro
(@bobstro)
Famed Member

As some of you know, I like to tinker with my Prusa Mk3 and figure out problems. Unfortunately, I was shipped a rock-solid Mk3 back in early 2018, before the MMU2 shipped, so apparently I've got an equally-reliable E3D heatbreak with no step. I'm using the original R2 parts, so I can't even get my PINDA probe to sag. I'm really feeling left-out.

I'm wondering if somebody with a known-bad, crappy and unusable modified Prusa heatbreak with the 2.2mm top bore would mind shipping it to me. Please PM if you're willing to do so. I'm located in the US, so local would probably be best. Happy to drop a fiver in the mail for shipping.

(Alternately, if somebody who is persistently having the issue would be willing to work with me out-of-band, I'd like to test something before making confusing public suggestions.)

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 : 06/09/2019 3:17 pm
vintagepc
(@vintagepc)
Noble Member

I'm not sure if I should share your resentment as my printer has an MMU heatbreak and it has not caused me any jams that were not my own doing (forgetting to open the enclosure for a PLA print...)

But I can send you some melted R4 parts if it makes you feel better 😛

 

Posted : 06/09/2019 5:24 pm
bobstro
(@bobstro)
Famed Member
Posted by: vintagepc

[...] But I can send you some melted R4 parts if it makes you feel better 😛

Heh. Not just yet. Let me see if I can make my own!

I'll feel foolish ordering a Prusa heatbreak in the hopes it fails. I'm assuming there are a few laying about unloved and looking for a new home. 

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 : 06/09/2019 5:37 pm
Tim
(@tim-m30)
Famed Member

I have a few ideas why some people experience the jam and some don't.  It's all about the finery of the actual installation, and a quarter turn makes all the difference. 

For example, my jams did not start until after replacing the first nozzle. And after several nozzle replacements the jams were routine.  I suspect the nozzle change added incremental changes to heat break height in the heater block.  Once the heat break migrated a quarter turn too high, the 2.2 mm step was out side the melt zone. 

Said another way, the Prusa heat break works if the heat break neck is biased into the heater block. If assembled per E3D and it's biased above the heater block, you get problems.

E3D-V6 Bias - neck is about 1/4 turn high

Versus Prusa version which has neck a bit more into the heater block.

 

It is always wise to get more than one opinion......
Posted : 06/09/2019 6:33 pm
vintagepc
(@vintagepc)
Noble Member

Logically, it would also give you less grief if you have a hot-end sock, since there is going to be a bit more heat migrating up to that area because it cannot radiate out the sides or bottom of the block. Interesting observation - I'll have to check my own assembly.

 

 

Posted : 06/09/2019 6:36 pm
Tim
(@tim-m30)
Famed Member

ps: one of the more recent jam reports has a stub that is undeniable proof the step is the issue. You can see the 1.75 / 2.20 / 2.00 steps quite clearly showing the melt point in that case is in the 2.0 mm section. Look closely and you can see the step down to the 2.0 mm section at the very tip, where plastic has work fractured and separated from the melt.

It is always wise to get more than one opinion......
Posted : 06/09/2019 6:39 pm
bobstro
(@bobstro)
Famed Member

Very possibly on all counts, but I'd just be speculating if I don't try it myself. Thus I'm still looking for a Prusa-fied heartbreak! 

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 : 06/09/2019 7:15 pm
Tim
(@tim-m30)
Famed Member
Posted by: bobstro

Very possibly on all counts, but I'd just be speculating if I don't try it myself. Thus I'm still looking for a Prusa-fied heartbreak! 

Do you own a 2018 MK3 ?  You already own the Prusa-fied heat break... lol.  What exactly are you planning to try?  Can you accurately cross section a few of the heat breaks to look for dissimilar bore? Build various test beds and precisely measure thermal characteristics along the cold to hot zones? 

PM an address and I'll mail you my relic.

It is always wise to get more than one opinion......
Posted : 06/09/2019 7:34 pm
david.a66
(@david-a66)
Honorable Member

interesting comments over in the 602 discord from the guys at Fusion Filaments - they think a lot of the jamming is the filament tempering as it moved in and out of the heated zone and the heatsink getting too warm. instead of replacing the heatbreak they increased the cooling fan flow 

Posted : 06/09/2019 10:16 pm
Tim
(@tim-m30)
Famed Member

This is not tempering: material is Poly-Carbonate no less

This post was modified 2 weeks ago by Tim
It is always wise to get more than one opinion......
Posted : 06/09/2019 10:18 pm
bobstro
(@bobstro)
Famed Member
Posted by: Tim
Do you own a 2018 MK3 ?  You already own the Prusa-fied heat break... lol. 
Mine's a March 2018 shipment. I may well have a Prusa-fied heatbreak, but mine's not acting up, so I want to try one that has been pinned for the crime and try a few things to prove/disprove some theories before I go blathering about it.
 
Has anybody nailed down when exactly Prusa started shipping the modified units? 
 
What exactly are you planning to try?  Can you accurately cross section a few of the heat breaks to look for dissimilar bore? Build various test beds and precisely measure thermal characteristics along the cold to hot zones? 
More just wondering if we're going to magically see this become less of a problem as we move into the cold months again this year. 

PM an address and I'll mail you my relic.

Done, thanks. Let me know what the shipping costs and where to send it!

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 : 07/09/2019 4:26 am
Tim
(@tim-m30)
Famed Member
Posted by: bobstro
Posted by: Tim
What exactly are you planning to try?  Can you accurately cross section a few of the heat breaks to look for dissimilar bore? Build various test beds and precisely measure thermal characteristics along the cold to hot zones? 
More just wondering if we're going to magically see this become less of a problem as we move into the cold months again this year. 

My printer is on a dining table in a climate controlled room that varies by +/-3 f depending on mood. 72 to 76 typically.   Not heat related at all in my case.  If anything, it is too cool.  But raising print temps 25c did nothing to change the failure characteristics -- I tried printing PLA at 240c to see if I could move the melt point -- it had zero effect. 

This post was modified 2 weeks ago 4 times by Tim
It is always wise to get more than one opinion......
Posted : 07/09/2019 7:05 am
bobstro
(@bobstro)
Famed Member

Here are my results with my current heatbreak:

The top black bit is from a normal PLA unload at 200C. The bottom white is rigid.ink floss cleaning filament after a cold pull (not a perfect one). In both cases, the widest bit (the tip on the black, collar above the tip on the white) are roughly 2.2mm. This indicates I have the "bad" 2.2mm bore hotend, no?

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 : 08/09/2019 11:01 pm
vintagepc
(@vintagepc)
Noble Member

I think you've been beaten to the punch, I just started watching this stream and realized "hey, this sounds familiar..."

 

 

 

Posted : 12/09/2019 12:20 am
bobstro
(@bobstro)
Famed Member
Posted by: vintagepc

I think you've been beaten to the punch, I just started watching this stream and realized "hey, this sounds familiar..."

I hadn't seen Chris' video before. Thanks for the link. His conclusions underscore the very reasons I want to do some more testing for myself. Replacement of the hotend is a band-aid being applied to the underlying issue of heat creep. We had a plethora of heat creep reports last year, and a variety of work-around were noted. Another spike as we moved into summer this year, and another work-around was noted. Work-around are fine -- you still want to print after all -- but I think this issue is far more complicated than simply identifying one adjustment and declaring mission accomplished.

Chris did make a good point about the default fan supplied with the E3D V6 moving more air than the Noctua provided by Prusa. I'm still puzzled as to why my OG R2 extruder config is not causing me the issue if using the same heatbreak design. This piece printed with a 0.25mm nozzle and 0.04mm layer heights without significant problems:

Also very interesting that the E3D titanium heatbreak uses a larger bore than the default. Wouldn't it then suffer the same step as the filament moves from the wider heatbreak bore into the smaller nozzle? Anybody aware of testing done with the titanium heatbreak?

Does anybody have any suggestions for a good benchmark piece? It's always helpful if testing with the same part.

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 : 12/09/2019 5:37 am
Tim
(@tim-m30)
Famed Member

My fan and heat sink were meticulously cleaned - probably nothing to do with the jams I had.   It was jamming before I changed nozzles, and jamming after I changed nozzles (including nickel/copper).  So unlikely caused by assembly tolerances, either.  I didn't see any conclusions reached in the video - just a guess "it could be the heat break" ...  

The nozzle is beyond the melt point, so there will be no jams with the titanium version.

The issue is material builds up in the neck - above the step - where the plastic can't melt. And 2.2 mm filament is too much for the extruder to push down the 2.0 mm cold pipe below the step.  

The only way I see to identify the problem methodically is to use a high resolution thermal camera to log the temperature of the hot end, from heater block up to heat sink: the gradient must be captured with sufficient resolution to show if the step bevel is anywhere near the melt point. 

A secondary systemic feature of the jam is flow related.  This may explain why some see the issue and others aren't bothered by it.  It may also be related to the characteristics of the filament being printed.  Slightly lower melt point, slightly higher melt point, flow characteristics or viscosity.

As for a sample to test with: the ones that were causing me grief were 30 hours into the print when they failed (28-30 mm up the 120 mm part). 

This is the apprx location it failed: Literally hundreds of long and short tracks, lots of retraction, and probably Z moves.  I didn't keep the gcodes, but I believe it was sliced 0.1 mm layers, 0.40 mm nozzle, Prusa PLA profile most likely modified for rectilinear infill pattern and warmer bed temps, Amolen or Zi-Rui Marble PLA, room conditioned around 23 to 25 c, it was mid April, room humidity around 20%. 

It is always wise to get more than one opinion......
Posted : 12/09/2019 8:29 am
chocki
(@chocki)
Reputable Member

According to the E3d documentation, the heatbreak does not stick up proud of the heater block, but sits flush with it, just like the Prusa version.

https://e3d-online.dozuki.com/Document/n5grN2JNoNibYeQW/V6-175-ASSM.pdf

Normal people believe that if it ain’t broke, don’t fix it. Engineers believe that if it ain’t broke, it doesn’t have enough features yet....
Posted : 12/09/2019 4:28 pm
Tim
(@tim-m30)
Famed Member
Posted by: chocki

According to the E3d documentation, the heatbreak does not stick up proud of the heater block, but sits flush with it, just like the Prusa version.

https://e3d-online.dozuki.com/Document/n5grN2JNoNibYeQW/V6-175-ASSM.pdf

I don't quite understand what you are saying.   The heater block assembly images I posted above are from E3D and Prusa web sites.  I haven't seen any examples of the heat break being too far out of the heater block except where users have improperly replaced their nozzles and are having leaks.  It's never been an obvious issue with heat break jams.  The only variation I've seen there is a quarter turn plus or minus.  Too close to call a problem -- or if it is a problem -- that's a very fine line to deal with.

 

ps:

https://e3d-online.dozuki.com/Guide/V6+Assembly/6

https://d17kynu4zpq5hy.cloudfront.net/igi/e3d-online/FDbyHPQO56Df3jKC.large

This post was modified 1 week ago 3 times by Tim
It is always wise to get more than one opinion......
Posted : 12/09/2019 7:58 pm
chocki
(@chocki)
Reputable Member

I do apologise, I have never seen those step by step instructions and just went by the drawings, where in all of them it shows the heat break sitting flush with the heater block, this leaves exactly 1 mm of gap between the top of the nozzle hex nut and heater block.

 

This is how my print head arrived and how I have kept things since.

Yep, cant disagree, those instructions clearly show the heat break sitting proud which would leave less gap between the nozzle and heated block but as long as less than 1mm of the heatbreak is showing above the heatblock, then there should be no issues.

I wonder why they did not make the heatbreak so that it has a small lip so that you screw it fully up to the lip into the heatblock, then it's set correctly. A small 45 Deg taper would work as well.

 

I've just thought, I wonder if this could be the reason some users are having the extruder melt above the heater block, because the heatbreak is screwed in just that little bit further?

This post was modified 1 week ago by chocki
Normal people believe that if it ain’t broke, don’t fix it. Engineers believe that if it ain’t broke, it doesn’t have enough features yet....
Posted : 12/09/2019 9:42 pm
Tim
(@tim-m30)
Famed Member

I'm not a metals expert, but it's hard for me to imagine the thermal gradient in the heat break being so dramatic that the heater block is 210c, and a millimeter up is 125c.   I don't have any measurement gear micro enough to measure the heat break neck accurately but not corrupt the measurement at the same time.  Hence I'd need to ask friends at Flir if they have a camera I can borrow... but I'm not sure I want to invest this type of goodwill for Prusa ... lol.  

I'm somewhat confident in my case the PLA is melting lower than the step, then being forcibly "oozed" upward during printing, where it fills the 2.2 mm void surrounding the filament, cools, hardens, then jams as material below vacates and the extruder tries to push out more filament.

I think those using mostly default settings are more prone to have this issue. People comfortable using their own personal tweaks, like low or no retraction, are less prone.  And then the very simple fact some parts are worse than others.  I never had a jam printing boxes, many organic shapes, or even multi-day (14 in total) masks.  But a few parts were a problem: especially castles with lots of crenelations: discrete small points on the part that required stopping and restarting flow in rapid succession and separated by a small distance.  Thinking about it, a test piece of a simple wall structure with an SOS pattern as it builds may be a good candidate... and a couple of long strips to force the jam condition after the sequence of dashes.

 

ps: the engineer in me agrees the heat break neck should sit flush in the heater block, but the photos say different. {shrugs}

This post was modified 1 week ago by Tim
It is always wise to get more than one opinion......
Posted : 13/09/2019 12:13 am
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