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bubbles in PETG prints?

Posted: Mon Jul 02, 2018 5:09 pm
by jferguson
This is a wing section I'm designing to use on a foam r/c plane. Wingspan wil be 52 inches and each of these sections is a bit over 7 inches long - length determined by rib geometry. Filament is fresh Exun PETG Clear. I'm using the PETG profile shared on this site.

So why am I getting what appear to be bubbles on the leading edge? There are random bubbles elsewhere on the print but not in any pattern I could discover.
IN the end, these sections will be sanded and painted. I did clear PETG because guys at think it's stronger in terms of adjacent layer adherence than colored filament. My direct experience is that if it is stronger, it isn't enough to be apparent to me.

What variable might I tweak?


Re: bubbles in PETG prints?

Posted: Mon Jul 02, 2018 6:05 pm
by airscapes
Seems to be moisture and that can happen before it is made according to something I read on another site some time ago.
I have a dehydrator I run all my filament in to dry it out if I run into problems.

Did a quick search found this on the matterhackers sites
Been Printing with the MatterHackers PETG using a wide Nozzle with interesting results using a Raise 3d N2+, printing on 80C bed of carbon fiber composite coated with hairspray, nozzle is 800 um Stainless coated, printing single wall vase mode with the goal of maximum clarity, print speed at 20mm/sec:
1) The BRAND NEW, in a vaccum sealed plastic bag had adsorbed enough water that it was not useable - printed bubbles every cm. If this happens to you, it is not a big deal - heat it at 50C overnight and it dries out and prints very nicely.
2) Tested out temperature variance and it was VERY wide and forgiving. Best results were between 210 and 240C (going for maximum wall clarity.) From 250 up to 280C the print became progressively more opaque and eventually had a granular surface. I found 220C optimal without a cooling fan directed at the print surface. (testing yellow and green)
3) You can print layer heights up to 100% of the nozzle size! I am printing 800 um layers through an 800 um nozzle. (the wall thickness of a single shell averages 920um at 800 um layer and 770 um at 500 um layer thickness). Why do this? Because it makes cool looking and thicker walled single wall vases.

And this ... e_changed/

And this video ... joshbishop

Re: bubbles in PETG prints?

Posted: Mon Jul 02, 2018 10:33 pm
by jferguson
print velocity might have an effect. there are far fewer bubbles in the straight runs. most of them are in the curves. i'm printing at 247C - maybe I ought to back off to 241 and see what effect it has. ??

Re: bubbles in PETG prints?

Posted: Mon Jul 02, 2018 11:25 pm
by airscapes
I have been using eSun white PETG and printing at 245 and I tend to print everything slow as I have been doing tiny stuff. I would not think speed would make bubbles.. I think I would probably try extruding as in the video and see if the bubble show up there.
If you have an electric oven, toaster oven or convection over ( Just can't use gas) you can dry the roll at 140-145 degrees F for 5-6 hours if the oven goes that low.
Good luck!

Re: bubbles in PETG prints?

Posted: Tue Jul 03, 2018 1:28 am
by jferguson
i was thinking that slower might make bubbles - filament might be hotter as it's layed down. gotta experiment.