[SOLVED] Bad quality when printing PETG

I have informed bambulab that the case can be closed. They have access to the thread (I have inserted the link when I opened the ticket a few weeks ago).
So I think it makes sense that they have already updated the values…

Ok, so I was right with my initial assumption that you‘ve increased the 75%+ value to 30mm/s and not the 50%+ value.
I’d suggest you edit your nightly post where you advise to change the 50%+ value to prevent any irritation.

That doesn’t diminish the brilliance of your findings at all. Congratulations, I’m very impressed.
Looking forward what other 3D printing issues you will come up with a solution for. :wink:

Cannot edit it anymore, seems some timeout ran out.

Maybe @T_guttata can edit his initial post as he did after your findings. So he must still have the permission to make edits.
In his edit he also falsely recommends to increase the 50%+ value instead of the 75%+ value.

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I made no error, just cited correctly;-)
But I have corrected the value!

I just noticed the discussion about which overhang speed bins get what values, and I see that the image in Thrawn’s message shows a 0.16mm profile being used.

The stock 0.16mm profile has these overhang speeds: 60/30/10/10
The stock 0.20mm profile has these overhang speeds: 0/50/30/10

Which stock profile are you guys using for the best results and at what speeds?

From Thrawn’s message:


Great Thrawn ! this is like the end of the film

I will anyway quote myself :stuck_out_tongue: from this thread on February the 5th

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@Thrawn You saved my day…

I was printing the Hydra AMS, with PLA, and having king of the same issues, printed twice with default settings, had same issues, at the same layers, i only changed the “slow down for overhangs” setting, now it print like a charm :slight_smile:


Disabling “slow down for overhangs” and ramping the bridging speed this high ruins the real bridging for me (when I need to bridge more than a hole).
I tried tuning PA again and discovered that the best value was 2x of what I was using before (0.098 instead of 0.045). Setting that value seemed to have almost fixed the issue.

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You can download the ORCA SLicer which is 95% the same interface. There you will find calibarion for temperature, flow rate and many other stuff.


Reporting back: I finally did run across a print where the OP’s problem happened to me. I’m now extra glad I followed this long thread, because Thrawn’s solution fixed it instantly. :innocent:


Thanks for this feed. I followed your guys suggestions & ran a benchy to test.
Overall not bad… I think I need to speed up on the bridges a little but very solid settings.
57minutes with the preheat, auto-level & calibration cycles.


After weeks of messing around with settings, going over half a dozen of different brand of filaments, I think I have finally figured out the biggest issue of PETG quality (overhangs). It is all about cooling. Nothing else matters as much as proper cooling.

The only thing that people need to change is drop down part fan towards 0 (0-30) and turn on AUX fan (up to 100%). The default is the opposite - part fan high and AUX fan 0.

This could also explain why people are getting different quality results - because some people print in hotter environments and some in colder and some print with open lids and some with closed.

I will make another post when I pull together all data from all brands and see what is really optimal.


That’s awesome - would love to hear more. Does this mean that maybe the part cooling fan is strong enough to push the molten PETG but not cool enough to “freeze” it in place first?

Just a general note for anyone new to Bambu. If Bambu doesn’t sell a filament, it usually means they haven’t been able to really optimize their profiles particularly well enough across many brands, so you can probably expect a higher level of risk that the default profiles might not work super well. Plain, non-CF reinforced PETG is notably absent from the filaments that they sell.

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I don’t think so, because even their PETG-CF profile for their filament can get better results with some additional changes. But there lies the first hint about cooling - their PETG-CF has much lower cooling values (0-30) compared to their generic PETG (40-90).

I can give some rough values I use for every PETG filament I tested so far and they all work about the same (Overture, Prusa, PolyLite, eSun):

  1. Bump up bed heating a bit, so the parts really stick (75-80) if you use textured plate.
  2. Increase nozzle temp to 265 for better layer adhesion and shiny look. Lower temps do not help for better quality, but just make the print less sturdy. I keep 1st layer at 255 to reduce oozing (because 1st layer is also slower).
  3. Main part cooling min set to 0, max to 20. Set AUX fan to 90.
  4. Set chamber fan to max (we want good ventilation around the part, but not directly on part); you do this with filament start G-code: M106 P3 S255

This should work for ANY PETG filament and massively improve quality (no more blobs that stick randomly around the part and filament strings that curl up). Overhangs are massively improved.

To even further improve quality, you can reduce speeds. Default Bambu print profiles are very fast and optimised for PLA. I am still working on that to see which speeds I should reduce, so it is good for overall any type of model. A quick change you can do is to simply reduce any speed (apart from Travel) to less than 200, set Outer wall to 100-150 and Top surface to 100-150. Generally, a 1/3 decrease compared to PLA speeds. Changing anything else has almost 0 effect on quality.

Print with open door and open lid in a cool room.

Let me know how that works for you. These changes made the biggest improvement.


What you recommend for speed would requiere him to have a custom profile, but max vol speed of filament will cap those speed at a maximum of arround 140mm/s with the defaut Bambulab PeTG filament setting (10mm³/s)

Unless he use layer haight < 0.2, reducing speed is not the good way IMO.

Reducing the max volumetric speed of the filament is IMO a better way, your profile will auto adjust its speeds based on filament settings and you wil not need to keep & update tens of print profile for each new filament.


The max volumetric flow is not a problem - I have fully tested Prusa and Overture, both have over 20+, so it is in-pair with PLA.

This is benchy with eSun PETG, only changed filament settings as described above and then printed with Standard profile (no speed changed). Just look at these beautiful overhangs. As good as when printed with PLA.

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You missed my point, or yu misunderstood, or I have not well explained, does not matter

Was talking about this, wich is useless with a max volumetric speed that cannot enable such speed

EDIT: well to be more clear perhaps, he just have to reduce its filament max volumetric speed to a good value and he will not have to change any speeds on its print profile as they will adapt to its filament settings, got it ?

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You are right. Let me do another test after I figure out max vol. speed.

I have had excellent results with Hatchbox PETG and the stock profile. Here’s one of those random torture tests, hard to get a good image because of all the test bits, but that was printed using ‘generic petg’. The overhang capability is pretty impressive. The long bridge is 4" long. You can see some fuzz past about 70 degrees on the angle test. My latest issue with Hatchbox yellow PETG has been 90% solved using the textured PEI plate. Cutting the max nozzle temp to 250 and the flow to 0.9 got me the rest of the way. Otherwise, HB black, white, red, blue, gold have all worked fine.