Hi everyone, not so long ago I opened a thread on this very same issue being discussed here, I accidentally missed this one when looking around the forum before posting on my own…
Here is my experience, what I’ve tried and what I may try in the future. Keep in mind I still have this issue with Bambu PETG-CF and for me it completely makes this filament unusable as I can’t keep babysitting every print for hours and hours just for it to succeed. I’m also thinking about opening a support ticket to ask some questions directly from Bambu.
What pisses me off VERY much, is the type of this problem:
PETG can be a pain to print well and clearly has some downsides as any other 3D printing polymer.
What is amazing is how well carbon filling is contributing to the properties of PETG.
PETG oozes → PETG-CF oozes less
PETG glasslike finish showing every little surface issue → PETG-CF hides them being matte
PETG bridges poorly, poor overhangs → better overhangs with PETG-CF
PETG sometimes too flexible → PETG-CF stiffer
But, there is this downside that is the main culprit behind this problem as well: While you can print PETG with any brass nozzle, PETG-CF requires a hardened steel nozzle, as it is abrasive. Now PETG really likes to stick to steel nozzles, but now you have to use them. This is the core of the issue how I see it and I’ve yet to find a way around it. It is annoying that one of Bambu’s main selling points of this material is a modification that makes it stick less to steel, however it is the exact same thing happening for me. In fact it sticks more than any other PETG I’ve used, so I call BS marketing!
After opening the thread and trying suggestions from the comments as well as trying suggestions from this thread, sadly, nothing has made a difference significant enough to resolve the issue. I haven’t given up on this as I REALLY want PETG-CF to print well for me, it would be my go-to filament whenever something doesn’t just have to sit on a shelf collecting dust, but rather some applied model that needs to have decent properties.
Here is my takeaway of things that might help as of now, I will update this whenever I find something new:
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Just dry your filament once again, if you can’t make sure
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Clean the nozzle, inside, outside. As suggested by @djeZo888 you can swap nozzle covers and make sure there is no residue under the lip of the silicone cover.
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Make sure the layers are perfectly flat: if a tiny bit is sticking out it will be contributing to the blob.
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For this, tune your pressure advance and flow rate, rather than just letting the LIDAR get an approximate value. Orca lets you do all this pretty quickly with little effort. Minimal underextrusion is in this case in my experience prefered over overextrusion. PA values way higher than expected has helped me and the flow was lower than expected as well. Flow can be tricky to tune when using the Orca flowrate test, with PETG-CF you want the lines just touching, ignore the seam and little bulges on the sides, just look at the middle of the rectangles, PA tuning will help with that later. Other print settings that are important are:
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Infill type: should be rectangular or gyroid or anything non overlapping, NOT grid
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reduce infill overlap: Bambu’s 15% preset is imo way too high
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turn off ensure vertical wall thickness
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print inner/outer walls with same width
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reduce speeds and access, especially on outer walls
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try outer/inner and inner/outer wall order to see which works best. Inner/outer is preferred for me, as this material already has a sublime surface finish, and this way if there is an extrusion inconsistency, the material has more space to squish instead of bulging upwards.
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Arachne has helps a lot for me when printing thin features where inner walls don’t fit in perfectly
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Tune retraction and Z-hop. This was impossible for me with a retraction tower from Orca, as there was 0 stringing to begin with. You still want to find perfect settings so there won’t be anything sticking out upwards from the layer after an extrusion path.
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Try plastic repellant paint on the nozzle. Slice has something exactly for this issue (Plastic Repellent Paint™ | PTFE Nanosuspension | Slice Engineering). My expectations might have been to high, this did help a little but but did not resolve the issue. It wears quickly and I’ve found that getting some dry high temperature PTFE based spray yields similar results with it being cheaper and widely available (make sure it is rated up to at least 270°C).
The last and probably most important factor is the temperature. I’ve seen @cl33 mention trying different printing temperatures with no success, this was the case for me as well. However, I’m sure this issue would be reduced to almost no failed prints if I had the previous layer at the perfect temperature, when the next one is printed on it. This can be controlled purely by extrusion temperature, bed temperature, layer time, and mostly the fan speeds. I suspect this could single handedly solve this issue if set perfectly. Currently I’m playing around with this, I’ve seen @ant in a different post mentioning this but that is where that discussion ended. This is what I’m working on right now, I will post results if I have any.
Keep in mind, the prints that succeed are coming out perfectly, a few of the best prints I had with this printer was with Bambu PETG-CF. But this makes it impossible to print anything for more than a few hours without removing the buildup from the nozzle. Sometimes I get lucky and the blob just attaches to an outer wall or gets knocked down from the nozzle leaving only a little scar on the surface of the print, however if it attaches to an inner wall it makes the nozzle jump the next layer which leads to parts easily braking at that height.
Finally, MANY MANY MANY thanks to @3DTech, you are a champ and thanks for the many replies, long conversations and sharing your knowledge! @djeZo888 has some nice results and tips with PETG-CF as well, just click on his profile and look for his activity. Same goes for @Matt, he has amazing results with PETG-CF. Most of the bullet points are ideas mentioned in many threads (including this one), just thought I would collect the ones that helped a lot for my own sake and for anyone reading this.
If anyone suffering from this annoying issue finds a definitive solution, please don’t forget to share it so others can benefit from it as well.