PETG insanely brittle

Bambu Lab A1 Series Troubleshooting
1

Hey, im currently working on a functional part and did all the prototyping with PLA+ 2.0 on my A1. Now I want to print the parts with Sunlu/Jayo PETG to have the required strength. Problem is, that all the prints are extremly brittle OR lack detail, depending on the settings. With brittle I mean, the part just snaps (very easily), whereas the same model with PLA is bending without ever really breaking apart.

I dried the PETG (50C for 24 hours).

Settings I tried so far (0,4mm Nozzle, 0,20mm Default Profile):

Filament:

Temp: 245/255/260
Flow ratio: 1.0 (calibrated with Orca Slicer)
Pressure Advance: 0.0274 (calibrated with Orca Slicer)
Bed Temp: 70
Volumetric flow: 10/15/20

Cooling

No cooling for the first: 1/3 Layers
Min fan Speed: 10%, layer time 30s / 40%, layer time 30s
Max fan Speed: 40%, layer time 12s / 90%, layer time 1s
Min print speed: 10mm/s / 20mm/s

Speed

Default Speeds / All speeds down to 100mm/s (except Overhang and Acceleration)

Does anyone have a clue what I could try or share your settings? Iā€™m getting crazy here x).

2

I donā€™t know if this applies to your problem. I had a 2kg spool of Atomic PETG and had problems with moisture. So every time I printed with it I basically printed from a dryer. Over time I think I over heated that filament way too much and it became brittle. At least thatā€™s what I believe. Sections of the spool were useable but others kept breaking and I wasnā€™t using an AMS. You could snap the filament like uncooked spaghetti.

Now I keep the room as dry as possible and donā€™t dry over 50 deg and only for 6 hours. Iā€™m not really sure I need to dry PETG or PLA as Iā€™ve seen no moisture issues.

3

I print alot with Sunlu PETG. Never had that problem with DRIED filament. 50C takes forever to dry, if itā€™s even possible :sweat_smile:
But normaly if itā€™s not dried enough you should get strings, and/or you would ā€˜hearā€™ it.
Can you dry it at 65C for 8 hours and try again?
If itā€™s still brittle, here ya go:

Screenshot_20241119_233906_Bambu Handy
Screenshot_20241119_233906_Bambu Handy1439Ɨ2268 158 KB

4

Thanks guys, I just printed a test piece with an other roll, also dried for 24h and got the same results. I just started a print with a freshly opened spool without drying to see if I ā€œoverdried?ā€ it.
If I get the same results here I will test your profile @Bjorn and if that also does not help I have to see what I can do, since my dryer only reaches 55C max.

5

I noticed what dean said about overdried. I doubt that, because my dryers (Sunlu S4 and Eibos Cyclops) are running 24/7 at 65C with PETG in them, just so i always have filament ready for when i need them. For single color prints i print directly from the dryers.
If 55C is your maximum you could use your bed as a dryer, just follow bambus recommendations. Use that as a last action :smiley:

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Ye, I just verified that. Printed with a freshly opened spool, popping noises while extruding, stringing and blobs on print. But still brittle as the dried one. I am now printing a test piece with your profile, wish me luck :smile:

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Yea a fresh spool should be thrown in the dryer right away! Unless itā€™s PLA :sweat_smile:
Use the latest profile from there, i did not know how update it before so i added a new one, hehā€¦ Going to bed now, but gonna check back when i wake up and see how it went!
Good luck! :raised_hands:

1 Like
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Have to go to sleep aswell now, will follow up tomorrow evening :slight_smile:

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Spools can arrive in sealed bags with desiccant with all kinds of moisture levels. The bags may be water permeable or maybe the desiccant they use isnā€™t dry to begin with. At any rate, put a spool fresh from a bag into a gallon freezer Ziplock with a hygrometer and seal it. In 10-12 hours youā€™ll have a number proportional to the filament moisture content. Bet itā€™s fairly high.

The popping sound is an indication of high moisture content, though. The stringing and blobs are also signs of moisture in PETG.

Since the new spool was already popping and stringing, Iā€™ll guess it wonā€™t print well either. Thereā€™s a number of threads here on drying. Unfortunately it sounds like you get to take that journey.

I had to as well with PETG HF. Drying made a huge difference for my prints. But itā€™s important to know you actually are drying. Good scales can see the water loss but that bag and hygrometer test works great. Itā€™s just a little slow.

10

Alright, so I printed the test piece (used in this strength test rig: Flex-Tester for temperature calibration by alfrank - Thingiverse) with your settings. The print is stronger! but the visuals/precision is very bad, like distortions everywhere. Iā€™m really lost here. Also dried the filament for 8 hours with 65c (weight is exactly the amount of filament + spool), so thatā€™s fine. Maybe I just have to give up and try an other brandā€¦ idk

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Not necessarily. Filament manufacturers use special ovens to dry filament. They donā€™t explain that their drying at 8 hours and 65C works in their special ovens but is only a guideline with consumer filament dryers.

If you want to know if your drying is effective, do the Ziplock bag test I described above with a spool fresh out of your filament dryer. Itā€™s the easiest way to know if your drying is effective and not have to guess.

High ambient humidity can stop drying in its tracks. If you arenā€™t monitoring humidity during the dry, you may be drying and you may not. Since you are seeing print defects, Iā€™m guessing you arenā€™t drying as effectively as you may think you are.

12

Good to hear! The problem here is cooling/layer time. A tiny, but tall object can take some tinkering to get good.
Print another model, something laying down or bigger, that gives enough time for the model to cool down between layers.

13

Good info to know! Thanks for sharing!

1 Like
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I sat on this for the last days and couldnā€™t give up. I bought a dryer that is capable of 80c and dried the PETG again for 8h @ 65c. The strength and appereance was the same. Next I calibrated everything again and got the best results with the following settings:

Nozzle temp: 250c
Bed temp: 70c (75c for taller stuff)
Flow ratio: 0.97
Pressure advance: 0.0395
Volumetric speed: 13mmĀ²/s
Retraction length: 0.2mm
Min fan speed threshold: 10% | Layer time 30s
Max fan speed threshold: 20% | Layer time 12s

Following that I printed the test piece again, the strength was (minimal) better, but still very brittle. So I began to read some articles about PETG and factors that influence the strength. Below a summary of tips I found online and want to share for other people that might have the same problem as me.

Wetness:
The PETG should be fully dried, because wetness reduces strength alot (among reducing other things like stringing, holes, etcā€¦).

Speed:
Many people say, that PETG should be printed at low volumetric speed and adjusted general speed (like outer wall, inner wall, infill). While this is kinda true, I tested the strength for several (volumetric/general) speeds and couldnā€™t find a meaningful difference between them.
After running the max flowrate calibration I reached a maximum flawless volumetric speed of 16mmĀ²/s (I settled for 13mmĀ²/s just to be safe).

Temperature:
Alot of people stated the temperature is too low for good layer adhesion and therefore should be raised. After several temperature tests together with adjustments to flow ratio and speed, I got the best results in the range of 240-250c. The layer adhesion was the best at 250c.
Note that if you want to run at higher speeds a higher temperature helps alot, but brings cosmetic problems like stringing/distortions.

Fan Speed and Layer Time
Now this is were changes finally showed a meaningful difference in strength. After reading so many comments online, trying all of the above, the comment by @Bjorn inspired me to try fiddling with these settings.
I printed multiple tall thin pieces and changed the Maximum part fan speed by 10% every print, starting at 100% (Min fan speed was set at 10%).
The lower the fan speed was, the stronger the parts were. At 20% max fan speed the part was finally as tough as I needed it to be.
If I had printed an other model, with a higher layer time (above 12s), I wouldā€™ve never run into these problems, because then the fan would run at 10% on provide good enough layer adhesion.
Before these adjustments the test part just snapped like a thin piece of wood, now the print just bends and shows a little crack very late, while not breaking at all.

Conclusion
If you want to print a strong small part, adjust the fan speed and layer time accordingly. Thatā€™s also true if your print has small features, that need a good layer adhesion. Here you can adjust the gcode for these layers (M106 P1 SXXX, where XXX is a number between 0-255. 255 means 100% fan speed, while 128 is equal to 50%). Just remember to adjust the part fan before the other layers that donā€™t need the additional strenght).

I donā€™t know if anything I write here makes sense, but that is what worked for me. Maybe I can help someone with this write-up.

Next To-Doā€™s
Next up are test prints for overhangs and bridges, to see which settings perform the best here, while still maintaining a good strength.

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