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As stated above, I am trying to solve a problem I've had for a long time. Unfortunately, this has recently intensified to the point where it causes layer splitting/detaching from each other. I have tried various ways to fix this and, while decreasing the temperature and extrusion multiplier improved the situation, the problem is still present.

My settings:

  • Nozzle 235 °C Bed 100 °C
  • Cooling 25 %
  • Extrusion multiplier 0.89
  • Speed 150 mm/s for everything, 50 mm/s for small perimiters
  • Acceleration 1000 mm/s2, (default)
  • Layer height 0.15-0.3mm
  • Line width - 0.6mm for everything, but 0.45 for first layer and 0.42 for top solid infill

    Is there a different solution than lowering print speed or buying an E3D silicon sock? I have lost my spare ones and the current one wore down. Obviously, I can simply pause the print when I see plastic bulding up on the nozzle, but I am sure that there is a more efficient solution.

    UPDATE: I found that the hotend was very dirty and full of burnt/molten plastic. I am almost sure that the hotend is leaking somewhere between the heat block and the heat break. This didn't happen before I replaced the nozzle. How can I fix this? Do I have to replace the heat break or some other part?

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      $\begingroup$ PETG doesn't like to be printed at 150 mm/s usually advised speeds are in the region of 50 mm/s. Could be that because of the speed you build up blobs from left over pressure of the extrusion process which clutter and burn. $\endgroup$ – 0scar May 23 at 21:36
    • $\begingroup$ @0scar This is exactly what I was afraid of. I have no problems printing PLA, ABS, even Nylon at that speed... What is the highest possible speed do You recommend for PETG? I am working on a project where time is a limited resource, so I need to reduce print time somehow... $\endgroup$ – AAaAa May 23 at 21:49
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      $\begingroup$ @0scar it's also true that the layer height and line width are not mentioned... if thin and low, the volumetric flow would be reduced as well. $\endgroup$ – FarO May 26 at 14:20
    • $\begingroup$ @FarO The layer heights I use are anywhere between 0.15 and 0.3 mm. The problem occurs regardless of the layer height (in my case). Line width is 0.45 for first layer, 0.6 for external perimeters, 0.6 for other perimeters, 0.6 for infill, 0. 6solid infill, 0.42 top solid infill. I will include that in the question. $\endgroup$ – AAaAa May 31 at 12:37
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    I saw PETG printed at 100 mm/s, but 150! That's a lot.

    One solution to avoid blobs may be to limit the maximum speed to a value you can actually achieve with reliable results.

    Simple test to find your machine limits (each combination filament brand + nozzle + temperature has a different value): extrude filament in the air at increasing speeds, see how the flow changes, and when you see more than 5% decrease, that's it.

    1. M83
    2. mark the filament as if you were calibrating the E steps
    3. calculate filament speed: speed = volum/s / filament surface * 60 = mm^3/s * 25 (this factor is valid for 1.75 mm filament)
    4. set extrusion speed for 2 mm^3/s: G1 F50
    5. extrude 50 mm: G1 E50
    6. measure actual length extruded
    7. repeat 2.-6. but increase the speed by 2 mm^3/s each time: 2, 4, 6, 8, 10, 12, ...
    8. at a certain speed you will see that the actual filament length starts to decrease. When you see that the underextrusion reaches 5-10% (depending how much underextrusion you accept), write down that volumetric speed (mm^3/s) somewhere, it's your limit for THAT filament + THAT nozzle + THAT temperature
    9. Either a) calculate the max print speed = volumetric speed / layer height / line width or b) set the maximum volumetric flow rate in the slicing software so that the speed will be automatically capped taking into account layer height and line width. Prusaslicer allows to set that in the "Print" or in "Filament" settings, I recommend it for "Filament" settings, since it's a filament-dependent parameter.

    Example data from CNC Kitchen:

    enter image description here

    You can increase the max print speed, at the price of a little loss of quality around edges, if you calibrate the E steps at a speed corresponding to 2-3% underextrusion (alternative: to the speed of outer perimeters).

    This way you know that when you print slower than that (uncommon... typically only sharp corners and small perimeters) you'll get up to 2-3% overextrusion, and you extend by 2-3% the maximum print speed, since your max speed is the one where you get 5-10% underextrusion compared to your E steps calibration speed.

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      $\begingroup$ For info: if anyone perform that sequence to test the capabilities of their printer, please post the values here because I'm curious about the performances of various extruders. $\endgroup$ – FarO May 25 at 13:36
    • $\begingroup$ This seems interesting. I'll give it a try and let you know. $\endgroup$ – AAaAa May 26 at 12:56
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    Even not extruding anything but just performing travel moves over PETG at 100 mm/s or higher will tear it up and drag material all over the place. The result is blobs stuck to the nozzle, possibly even stringing, and choppy lines that the next layer will not properly adhere to. PETG simply cannot be printed at these kind of speeds regardless of how fast your hotend can melt it.

    Turn all speeds, print and travel, down to 40-50 mm/s, then experiment to see if you can increase them at all.

    Note that if your acceleration is only 1000 mm/s², you're basically never going to reach the desired 150 mm/s anyway, so this probably won't be as much of a slowdown as you expect. Jack the acceleration up as high as your machine can handle and it might still print as fast or faster, but without the blobs.

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