burned(?) PETG in prints

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jferguson
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burned(?) PETG in prints

Post by jferguson » Sat Nov 10, 2018 5:15 pm

I seem to be getting this problem on most of my PETG prints. I'm using E-Sun "natural" THe PETG settings recommended at this site, 247C Extruder, 87C Bed, and in this case 100% cooling on from second layer.

I get these inclusions of burned filament every so often. See photos.

What do you think is causing this? Have you had this problem?
prob-detail11.JPG
overall.JPG

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ednisley
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Re: burned(?) PETG in prints

Post by ednisley » Sat Nov 10, 2018 7:43 pm

jferguson wrote:
Sat Nov 10, 2018 5:15 pm
What do you think is causing this?
The other end of each fine hair you see on your PETG objects melts back onto the nozzle, accumulates into an oxidized blob, and eventually smears onto whatever's underneath, usually in the most conspicuous location.

Minimizing the hairs by getting retraction dead-on helps a lot.

After tweaking retraction, some folks swear polishing the nozzle to a high shine produces a non-stick surface. I added a silicone rubber coating for the same effect:
https://softsolder.com/2018/02/08/m2-no ... tallation/

Image

Looks hideous, works fine …

airscapes
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Re: burned(?) PETG in prints

Post by airscapes » Sat Nov 10, 2018 7:44 pm

I have seen that a few times with my white Esun PETG. It happens when plastic get stuck to the nozzle and eventually fall on to the part. Having your starting height perfect is a must along with sufficient retraction to prevent strings. I have found with my M2 using S3D that reducing the default X/Y speed on the speed tab, from 300 to 200mmS significantly reduces stringing and does not affect the print time too bad. Also slow down, stay around 40mms or less seems to be best for PETG.
I also use this brush https://www.ebay.com/itm/Tire-Repair-Br ... :rk:1:pf:0 to buff the nozzle after each print or when I see crud on it and try to wipe the nozzle with a paper towel before or after each print when it is at temperature.
Hope that helps!

jferguson
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Re: burned(?) PETG in prints

Post by jferguson » Sat Nov 10, 2018 10:46 pm

Thanks guys. I'll try what you suggest and let you know.

Phil
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Re: burned(?) PETG in prints

Post by Phil » Mon Nov 12, 2018 3:17 pm

It is probably the issue discussed above, but it could possibly be in the filament before printing. I had an issue with this:
IMG_0140.jpg
It was several meters long in the middle of the 1 kg spool. The company immediately replace the filament, so I will not bad-mouth them.
The burnt lumps were big enough to clog the input tube, disrupting my print. If smaller, they might have gone through and produced the effect you are seeing.

jferguson
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Re: burned(?) PETG in prints

Post by jferguson » Mon Nov 12, 2018 9:25 pm

ednisley wrote:
Sat Nov 10, 2018 7:43 pm


Image

Looks hideous, works fine …
Ed,
Is this the nozzle you currently use? I ask because I agree that it isn't pretty. On the other hand, I run things which worked from the start and which I'd planned to make nicer versions of, but then went on to just using them as they were. I find that I have the high-temp silicone left over from making the reflow oven. I think I'll make a couple of them and try to leave enough of the hex to enable me to remove them.

thanks for the great idea,

John

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ednisley
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Re: burned(?) PETG in prints

Post by ednisley » Tue Nov 13, 2018 1:32 am

jferguson wrote:
Mon Nov 12, 2018 9:25 pm
just using them as they were
The guy who gave me the idea made a positive duplicate of the nozzle, created a negative mold of a boot surrounding it, then cast silicone rubber into the mold to make the boot. I liked the silicone boot idea, but all the mold-making & casting seemed like way too much work, so I just troweled it on and it's worked fine ever since.

It's pretty much lost in the visual noise of the Basement Laboratory anyway …

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zemlin
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Re: burned(?) PETG in prints

Post by zemlin » Tue Nov 20, 2018 6:37 pm

It's tough to get a perfectly clean clear or white PETG print.
To minimize nozzle pick-up I run with zero z-lift. Each lift generally creates a tiny string that will pick up on the nozzle next lap. I also keep travel moves over the part to keep ooze from depositing on the outer layer.

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