PETG rough edges and overhang walls

[Odie]

Hi there!

Fairly new user here, around 200 hours in printing (a few hours of printing other things with success, as well printing with PLA with success).
I have been trying to print this sword guard with Elegoo Rapid PETG on my P2S, but most of the time I have these rough edges and overhang walls.

As you can see in the pictures below, the edges are not quite sharp and smooth, while in the upper area of the picture the edges are in a great shape.
Also please don’t mind the remainings of the supports, I didn’t bother removing them completely as I saw the issue still persists.

I tried SUNLU PETG for a change, and while it’s a bit better, the issue still persists at the edges and around the overhang walls. This filament has not been dried at all, been in the drawer for a week or two now. Put it into the dryer for 3 or 4 hours in the morning before printing, most likely still has moisture in it. Regardless, the result is a bit better. Also, it’s not calibrated and I used the Generic PETG preset with dynamic flow enabled.

In Bambu Studio the overhang wall looks like this, and it prints the exact same plus the support, which I turned off so you can see what I mean.

Right now I do not own an AMS, but I heard that the support can be a different interface with it thus the supported surface is better. I cannot get an AMS for the next few months, I plan to purchase one later, until then I would like to try and fix, or work around these issues if possible.

I’m using these printer settings below:

• Bambulab P2S (without AMS)

  • 0.4 Standard Nozzle

  • Textured PEI Plate

• Bambu Studio

• Elegoo Rapid PETG

  • I calibrated it through this video step by step

  • Flow ratio: 0.95

  • Plate temp: 70 C

  • Nozzle:

    • Initial layer: 240 C

    • Other layers: 240 C

  • Max volumetric speed: 8 mm/s (I started with 12 mm/s, then turned down to 8 mm/s)

  • Cooling min fan speed threshold: 20% (Layer time is 30s)

  • Cooling max fan speed threshold: 40% (Layer time is 12s)

  • Aux fan is completely turned off

  • Retraction length: 0.4mm

  • Z Hop when retract: 0.4mm

  • Z Hop Type: Spiral

• 0.12mm High Quality BBL P2S preset

  • Turned on Avoid crossing wall

  • Adjusted Sparse infill density to 25% from 15% (for the extra strength so it’s not brittle)

  • Turned down Bridge speed from 50mm/s to 20mm/s

  • Turned on Support

  • Changed Reduce infill retraction to Disabled

The filament has been in the dryer for over 40 hours now at 65 C, and it’s turned on even while printing. The dryer is a Creality Space Pi.

I prefer to print this in PETG because of the better heat resistance (it is for a cosplay), so I’m ready to cry and pray in the corner if that’s the best solution out there.

[Bullocks]

IMO you could use better flow dynamics, just go ahead and run the test, save the result.

Lots of small things you can try to get the overhang nicer after that

• Lower nozzle temp [~10c]
• • If you do, consider reducing speed or volumetric flow[~20%], to get a more complete melt
• The way this is shaped I would recommend normal support not tree, and make sure it creates with interfaces. Bonus points if you put the “Support Top Interface Spacing” [how dense the grid is, not the gap height] at 0 to give a more full interface.
• If you have an AMS, you can rig up PLA as a support with zero height gap. Set the filament change purge to max[900] in and out.
• A somewhat high-touch change is to alter your line width of outer wall to 0.40 [exact nozzle diameter]
• • Helps to ensure the “shoulder” of the overhang is attached to its neighbor wall, but it effects your overall squish, aesthetic, and strength

This shape is a great candidate to cut in half and peg/glue together the faces, but I understand if that isnt the approach you want

[CarbonForge]

It’s tough to tell, but it looks like both sides roughly overhang the same amount, but one is nice and the other isn’t.

That tells me it’s a cooling issue - likely there’s better airflow on one side of the nozzle than there is on the other.

Rotate your part 90 degrees so the two “wings” point forward and back, instead of side to side on the print bed.

Otherwise, you’ll need to look at improving part cooling airflow.

[Odie]

Thanks for the assists!

Seems like I missed to mention it, but I did a flow dynamics before and to me 0.035 K value looked ok, I will try it later.

I did, however, tried lowering the nozzle temp to 230c from 240c and with it the volumetric speed to 6mm from 8mm. It’s a bit more than 20%, but I think it’s fair enough.
Also used normal support rather than tree, plus set the top interface spacing to 0.

Please don’t mind the remainings of the support yet again, I just came home and been removing them since.
I think it came out a bit better, and imo I can work with this now. Some of the edges are still rough and not sharp, but not as terrible as it was before, so from this point I will only try to figure out how to smooth it out and get a better result for later projects.

Also, sadly the AMS is not an option right now as I don’t have it. I didn’t think I will need it when I bought the printer a month ago, but since it seems like a huge deal when printing supports as well, I have to buy one for sure.

However, I still do not understand why the overhang walls are like this when I slice it, and why not smooth? If I rotate the object and slice it, it kind of gets smoother, but somewhere else will look like this. First picture is the way the slicer auto rotates, and the second if I rotate.

[Odie]

Thanks for the assist!

After your reply I went and rotated it 90 degrees so the wings are facing the back and the glass.

I forgot to take a picture when it finished, that’s on me, but sadly the result was the same. A little bit better on the sides, but still not as good as I think it should be.

Also, and that’s on me too, I didn’t check which sides were nice and which weren’t, but since the issue still persists, I think I should work on improving the part cooling airflow.

Any tips where I can start? I looked up bambu’s wiki and did some research today, but a more experienced one probably can point out where to improve first.

[B_L_Account]

It sort of looks like that overhang area isn’t actually flat, is there a very slight curve to it? If so, it would make sense that the slicer is splicing that area up into weird lines instead of a single flat slice with rectilinear paths.

I would recommend that if you’re printing with 1 material at 0.12 layer height and need easy-to-remove supports, set the support Top Z Distance to 0.2 or maybe slightly less, which may require a couple tries to get correct for your model.

As a general note, when printing at 0.2 layer height, choosing 0.2 for Top Z Distance gives pretty reliable results for easy support removal. Layer heights lower than 0.2 will require some experimenting and experience, as they can be geometry/material dependent and finicky.

[CarbonForge]

Step one is figuring out what exactly is happening when it does work and when it doesn’t.

I’d suggest running the first part of your original print again to figure out which side is good and which side is bad. That helps narrow down what’s helping and beneficial so we can do more of this.

What’s the part cooling fan running at during these overhangs? If it’s not full speed, we can look at bumping it up. A more even flowing nozzle like the Biqu Panda…something may help.

[Odie]

Yes, there is a slight curve at the overhang parts, I would say max 3% angle. If I rotate the whole object, those lines disappear and they became flat, but then those overhang walls appear somewhere else.

I set the Top Z Distance to 0.2mm and it was a lot easier to remove, thank you! The surface is a lot better around the overhang walls, but these overhang walls are still the same as in the slicer.

[Odie]

Printed it again, and as I can see, the issue appears on right side at the back, and on the left side at the front of the wings.

The other sides of each end is ok.
As I can see it in the slicer, the fans are going at 50% to 90% at these parts.

However, the other sides has the same amount of fan speed, and those sides are ok.