PETG finish changes mid print

What would cause this kind of finish change in the middle of a print?

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I would guess temperature… Cooling fan? Chamber temp?

Temperature is my guess too but I don’t have any idea what is causing the change.

Did you check the different results at the sliced model? Sometimes you can see a change of the settings at these results that is also visible at the part (change of flow or velocity etc.)

Have you checked the cooling fan settings?

Are you printing another part at the same time? I did a quick google search and ran across a reddit post where they mentioned this as an issue. TLDR when you’re printing more than one part the layers of the parts have more time to cool, once the shorter part is finished the layers of the taller part have less time to cool. If you google “petg glossy to matte” you should come across the same post.

The printing speed changed probably due to min layer time setting. I noticed this on my 1st print, the Benchy. After the slowdown for overhangs is no longer required the print speeds up the outside walls and they become matte finish.

My cooling settings are the same as you have shown. But yes, this particular print has two objects printing and this part is the taller part, so the dividing line is where the other part was done. So It does seem clear that the faster printing/less time to cool is the issue on this particular object. I never noticed this before when printing with my Prusa printers, no doubt because they are much slower.

I’m quite new to the Bambu system. Short of separating the two objects and printing individually, do you have any suggestions for achieving the more glossy finish on the whole model?

Usually PETG is only matte when it’s printed at a lower temp, so you could try increasing your hotend temp and then adding a minimum layer time to get the upper faster layers to match the lower half of your part. In Bambu Studio it’s the option Filament → Cooling → Slow printing down for better layer cooling.

Thanks for your replies everyone, I do appreciate it.

I’m already printing at a pretty high temp (260C) but I’ll bump it up to 270 and see what happens. Also, I had already enabled the option to “slow printing down for better layer cooling” but I lowered the minimum print speed from 10mm/s to 5mm/s so we’ll see if that helps.

If it were me I would just print the parts separate instead of messing with my profile settings. Other than a minute or two for the bed leveling, you (usually) don’t save any time by printing more stuff at the same time like you would with a Resin 3D printer.

That will be the next option.

So, bumping up the nozzle temp helped a tiny bit but not nearly enough. And here’s the thing…this is happening on single object prints and not just with multi object prints.
It’s hard to tell in the photo but the 1-2 layers at the transition point are glossy and the rest is more matte.

If you want my X1C PETG configs send me a dm with your email address. I tried to upload them here, but apparently only pictures are allowed.
PETG is working great for me and the dimensional accuracy is pretty good. I measured this cube at 20.05mm x 20.05mm x 20.10mm, so slightly more in the z axis but not too bad.

I ran a test with two parts, they both look fine. The lighting is not very great, but I didn’t notice any differences in the finish of either part at any layer. This is using 3yr old Amazon Basics PETG which is now sold under the Overture brand.

What model is that. Looks great

It’s called Om Nom. I honestly don’t remember where I got it from originally, but I see there are a few different versions on Printables. One is already modified for multi-material, I might have to try that one. This one Printables has the same filename as the model I printed.

Thanks, i can see a busy weekend coming

That’s a great observation and explains so much!!! Thanks for sharing, Duane!

It normally doesn’t bug me to have the sheen change in the print, but if you want it to not change, set the speeds to be consistent all the way through the print. As speeds go up, I find the print gets more matte. Someone did some tests and found that extra temperature helps to mitigate it as the speeds go up, but that might be difficult to recreate for you. So I suggest slicing it and then checking the slowest normal speed (meaning super slow over hangs and what not can be disregarded). Once you see the speed the bulk of the print is being done at, set the max speed to that. That will keep the speeds and finish very consistent.

Many times you can look at the slicer’s speed preview and see layer for layer where the speed changes along with the matte look.

This is certainly correct. The best results I’ve been able to get came when I increased the nozzle temp by 10C and slowed down the printing on the smaller, upper part. It came out acceptable, but still not really where I’d like it. In contrast, when I decreased the temp a little bit the transition was much worse. At this point it is what it is and I’ll either live with it or print the parts separately.