[Résolu] PETG generates blob  

RE: PETG generates blob

Looks like overextruded filament, that has build up on your nozzle and finaly droped on your part.

A smaler extrusion multiplier might help. Make sure the nozzle is clean before you start the next print.

RE: PETG generates blob

Posted by: @lichtjaeger

Looks like overextruded filament, that has build up on your nozzle and finaly droped on your part.

A smaler extrusion multiplier might help. Make sure the nozzle is clean before you start the next print.

Nozzlescrubbing is one of my favourite pastimes 😉

How sensitive is the extrusion multiplier setting? What range of change is worth a try? -5%? -10%

Thanks heaps for the quick reply!

RE: PETG generates blob

I would start with 3%. So 0.97.

RE: PETG generates blob

@lichtjaeger

I'll give it a go as soon as the current attempt on the textured sheet is finished. It is quite annoying this time it prints absolutely perfect.

RE: PETG generates blob

Thanks lichtjaeger, that worked well.

Could you or somebody else kindly indulge my ignorance and point me to a good explanation what the extruder multiplier setting actually does and how it is different from the various extrusion speed settings?

RE: PETG generates blob

Your multiplier is how much material is actually being extruded. You can think of it in terms of volume. Trying to push to much material though a small opening. Eventually, nozzle pressure will rise to a point that it will either back up into the Hot End, or force its way out of the nozzle.

When it forces its way out of the nozzle, it generally creates unwanted Blobs or Zits in the prints at random intervals.

3DNewb

RE: PETG generates blob

Posted by: @h-waibel

[...] Could you or somebody else kindly indulge my ignorance and point me to a good explanation what the extruder multiplier setting actually does and how it is different from the various extrusion speed settings?

After looking into this myself, this is my understanding:

• Your slicer has no direct knowledge of the physical characteristics of your printer or filament other than what is entered in a default profile or by the user. There is no communication between the slicer and printer.
• The slicer therefore has to operate on assumptions regarding the amount of filament that will be extruded for any given command. The slicer output will only be as accurate as the settings it is instructed to work with.
• Unlike the slicer, the printer operates in the real world. Speeds, belt tension and friction vary, filament diameters are inconsistent. If the physical printer or filament varies in some way from the slicer's understanding, there will be discrepancies -- usually small -- between the amount of filament extruded, either a bit too much or a bit too little.
• A bit too much extrusion leads to blob and stringing. Many slicers incorporate retraction, z-hop, coasting, wiping and a host of other work-arounds to try to deal with the resulting stringing and blobbing. Too little extrusion and you can have fragile prints or gaps.
• The more closely you can match your slicer settings to the physical printer and filament characteristics, the closer the slicer's expectations will match the physical results.
• For many common (and particularly low-cost) printers, calibration of the steps-per-mm rate is required. The Prusa printers are manufactured with a high degree of repeatability, so the common "measure 100mm" calibration (e.g. MattsHub) yields only marginal benefits as the results will usually be within 1-2% of the Prusa default. That procedure only sets a baseline in any case, as different filaments can still vary.
• Prusa has provided carefully calibrated profiles for the printer settings that include acceleration and jerk values that are tuned to the printer hardware, providing the slicer with more accurate values than just a default.
• However, filaments still vary. The extrusion multiplier is where we can compensate for this variation on a per-filament basis. If you calibrate your extrusion multiplier and average filament diameter settings in the slicer filament settings, you'll have less over-extrusion.
• Less over-extrusion means you should see less blobbing, smoother z-seams and reduced stringing. This means you can reduce time-consuming extruder moves during the print. I find I can get by with 0.4mm retraction (often less), 0.4mm z-lift and no wiping once I calibrate my filament settings. IME, this applies to PLA and PETG.
• Prusa has recently provided retraction over-rides in filament profiles for additional tweaking for specific filaments rather than only providing one system-wide default. This allows the user to create highly accurate filament profiles.
• Linear Advance is to calculate appropriate variations in flow rate based on printer acceleration and jerk as it speeds up and slows down at turns. You want to include Linear Advance calibration in your filament profile development routine.

The extrusion multiplier is where you make tweaks for prints based on a specific filament rather than every print.

RE: PETG generates blob

Thank you very much bobstro, I slowly start to get a vague idea...

So my probably overly simplistic understanding is that the extrusion multiplier is a general modifier that is applied to all individual parameters that deal with extrusion (bridge speed, if speed, etc...)?

At least it now makes sense to me why it is in the filament specific parts of the settings.

RE: PETG generates blob

Posted by: @h-waibel

[...] So my probably overly simplistic understanding is that the extrusion multiplier is a general modifier that is applied to all individual parameters that deal with extrusion (bridge speed, if speed, etc...)?

My understandings is that it's used for calculating any gcode involving extrusion, yes.

RE: PETG generates blob

I have to agree with bobstro, I have been battling this, and didn't want to adjust the flow from my calibrated extrusion multiplier. I need my parts to fit together tightly. So I have reduced this plus blobs and zits by doing the Linear Advance calibration dialing in each filament that has no profile on this site adjusting the K-Factor as in the calibration routine has made this problem become history. Good luck.

RE: PETG generates blob

Thank you! 0.97 did the trick! I was fighting with crazy blobs and stringing and kind of at a loss. Ran into this thread and this setting solved everything. Thanks!