Heat Creep issue suspected with 0.25mm nozzle printing on my Mk3
 
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Heat Creep issue suspected with 0.25mm nozzle printing on my Mk3  

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printingrookie
(@printingrookie)
Eminent Member
Topic starter answered:
RE: Heat Creep issue suspected with 0.25mm nozzle printing on my Mk3

I printed a successful 8 hour print last night with another filament, and now printing in white with no issues. I believe the filament given by Prusa is just bad. Probably due to shipping and irregular ambient heating during that.

Posted : 08/10/2019 4:21 am
printingrookie
(@printingrookie)
Eminent Member
Topic starter answered:
RE: Heat Creep issue suspected with 0.25mm nozzle printing on my Mk3

@tim-m30

The Mk3 is completely flush and the Mk3s is similar to your picture. The issue happened with both printers. Changing the filament fixed my issue.

Posted : 08/10/2019 4:22 am
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Illustrious Member
RE: Heat Creep issue suspected with 0.25mm nozzle printing on my Mk3
Posted by: @christoph-e5

I would have interpreted the OPs image differently - bulge on the right side of the image is in my opinion partially heated material fused to the filament strand.

Looking on the OP filament image and the short color transition zone from mottled grey to more substantial black before the stretch zone i wonder if there is some kind of heat (the lack of..)  issue involved. Might be just the light on the image.

What you see is filament hitting the step in the heat break.  Filament is 1.75mm, before the step melt is 2.2 mm and usually forms during heavy retraction when the extruder is pumping hard, and then teh 2.0 mm section of the heat break. The melt point is the nozzle or just above the nozzle (1 mm into the heat break). This entire region is 2.0 mm. When unloading the filament melts and you get the tip shown.

Here's other examples:

Posted : 08/10/2019 6:58 am
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Illustrious Member
RE: Heat Creep issue suspected with 0.25mm nozzle printing on my Mk3
Posted by: @printingrookie

@tim-m30

The Mk3 is completely flush and the Mk3s is similar to your picture. The issue happened with both printers. Changing the filament fixed my issue.

I hope the issue is gone.  The MK3 is probably assembled wrong: the nozzle should not be jammed against the heater block. That would mean the seal between the nozzle and heat break, and the thermal connection, is not correct; it can also leak.  But if it's working... 

Posted : 08/10/2019 7:02 am
ACE
 ACE
(@ace-2)
Trusted Member
RE: Heat Creep issue suspected with 0.25mm nozzle printing on my Mk3

@bobstro I take back the success with 14mm³ and pla. tried some other models today and it was too much. In both cases Slicer has shown max volumetric as 14mm³ used in the models. either the graphing of volumetric speed is incorrect or the calculations are I think.

In my understanding either you can or you can‘t achieve a volumetric speed with a given setup and it should not depend on the model sliced.

Posted : 08/10/2019 9:58 pm
bobstro
(@bobstro)
Illustrious Member
RE: Heat Creep issue suspected with 0.25mm nozzle printing on my Mk3
Posted by: @christoph-e5

@bobstro I take back the success with 14mm³ and pla. tried some other models today and it was too much. In both cases Slicer has shown max volumetric as 14mm³ used in the models. either the graphing of volumetric speed is incorrect or the calculations are I think.

I spent a lot of time researching maximum volumetric throughput some months back and quickly determined that using a slicer introduces a lot of variables that can make the process more complicated than necessary. While PrusaSlicer can preview the maximum extrusion rate used during slicing, in reality speeds (and thus throughput) vary throughout the print as the nozzle accelerates and slows down. The actual rate is not fixed throughout a layer, particularly on smaller parts where acceleration and jerk have a proportionally high impact. I can't say whether the preview leans towards higher or lower averages for display.

In my understanding either you can or you can‘t achieve a volumetric speed with a given setup and it should not depend on the model sliced.

That's why I researched the ancient scrolls (google) of 3D printing and opted for the "free air extrusion" method of calibrating volumetric throughput. The idea is that you simply raise Z, heat the nozzle to a desired printing temp and begin extruding filament at gradually increasing speed until you notice feed issues (extruder clicks). Reduce in smaller increments until you find a speed that you can can reliably extrude at. This completely removes the slicer from the equation, making testing much simpler.

There is no one fixed "maximum extrusion rate" for a hotend.

  • Nozzle temperatures matter. Higher temperatures will allow you to extrude at increased rates. Of course, print quality begins to suffer at some point. Interestingly, nozzle material seems to matter at lower temps, but only slightly.
  • Nozzle size matters. Smaller nozzles result in increased back pressure, thus reducing maximum volumetric rates.

In my initial testing (documented on the linked page) I was using PLA with a 0.40mm nozzle at typical printing temps. I found that printing this (eSun PLA+) filament at 195C resulted consistently in skipping just under 15mm^3/s (Prusa's default), so I've gone with a conservatively low recommendation of 11.5mm^3/s for PLA with the E3D V6. This setting works well for most situations, but you can always tune to a higher rate based on your preferred filament and printing temps. Your 14mm^3/s is pretty close to the maximum I was getting.

I intend to do more testing with both larger and smaller nozzles. With larger nozzles, I was getting significantly higher throughput without feed problems, but I didn't complete the testing. I'm expecting volumetric rates to increase in proportion to the nozzle opening size (area) due to reduced back pressure (a nozzle > 1.75mm should extrude with no clicking), but I want to confirm this before making too many assumptions.

In practice, I like to use a somewhat lower Maximum Volumetric Speed (MVS) rating than Prusa's 15mm^3/s for PLA, using 11.5mm^3/s. In a perfect world, I'd take the time to identify the best printing temp for a filament and calibrate MVS for each filament, but I haven't gone that far yet. If anybody experiences problem with extruder clicks and feed issues, I always recommend backing speeds off as a good 1st test. If that works, you can tweak MVS to work around the issue.

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 : 09/10/2019 3:28 am
printingrookie
(@printingrookie)
Eminent Member
Topic starter answered:
RE: Heat Creep issue suspected with 0.25mm nozzle printing on my Mk3
Posted by: @tim-m30
Posted by: @printingrookie

@tim-m30

The Mk3 is completely flush and the Mk3s is similar to your picture. The issue happened with both printers. Changing the filament fixed my issue.

I hope the issue is gone.  The MK3 is probably assembled wrong: the nozzle should not be jammed against the heater block. That would mean the seal between the nozzle and heat break, and the thermal connection, is not correct; it can also leak.  But if it's working... 

Both my MK3 and MK3S were pre-assembled. The S doesn’t have the nozzle flush with the block, but still has the same problem with 0.25mm nozzle using the same filament. 

 

what’s the best way to prevent this from happening in the future? If it is indeed some heat creep, is there no way I can patch-fix it without disassembly?

 

 

Posted : 10/10/2019 9:41 am
bobstro
(@bobstro)
Illustrious Member
RE: Heat Creep issue suspected with 0.25mm nozzle printing on my Mk3
Posted by: @printingrookie

Both my MK3 and MK3S were pre-assembled. The S doesn’t have the nozzle flush with the block, but still has the same problem with 0.25mm nozzle using the same filament. 

I thought you were OK with a different filament? 

what’s the best way to prevent this from happening in the future? If it is indeed some heat creep, is there no way I can patch-fix it without disassembly?

Different filaments have different characteristics. If I encounter a problem with a new filament using settings that have otherwise worked with the same hardware setup, I simply dial back speeds to 50% using the front knob to verify that this resolves the problem. If so, I adjust the Maximum Volumetric Speed under the Advanced filament settings.

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 : 10/10/2019 3:06 pm
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(@)
Illustrious Member
RE: Heat Creep issue suspected with 0.25mm nozzle printing on my Mk3
Posted by: @printingrookie

Guys I've been using the Silver filament that comes with the MK3 printer, but it's not prusament.  I just changed to a local brand which is black and it's printing an hour in, could it be the filament???

Another poster just replied that his jam problem went away when he dumped the spools of the silver filament that came with his two new MK3S printers.  He tried the filament on the Prusas - both failed simple parts; so he tried the filament in his CR10S, and that also failed with a jam.  He concluded the filament is bad; and I'd concur.

Hopefully the new filament will work without incident.

Posted : 10/10/2019 7:24 pm
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