Hi all,
Any advice for 3d printing a water tight part with PETG filament? The idea is that the part would remain underwater for long (~indefinite) periods of time. Like a boat or floating aquarium decoration. Doesn’t need to be food safe.
Appreciate any thoughts on this.
christopher
Following, this sounds interesting 
This might sound like of topic but
If you need something to be water tight and not so much food safe, then why not print it using sla?
Many good reasons, potentially. Size, SLA printers do not have the same print volume as FDM. Post processing is a pain for SLA, and if your part can easily be printed FDM that would likely make it not worth it. Dimensional stability, SLA is pretty bad at this and large straight sections are prone to warping unless you have settings dialed in perfectly. Durability, PETG is a far more scratch resistant, chipping/shatter resistant, and UV resistant material than pretty much any reasonably priced SLA resin, which leads nicely to: cost. PETG is pretty dang cheap and resins can be expensive if you want particular properties.
Also I wouldn’t use SLA resin for anything going in an aquarium. Wouldn’t want to leach toxins for the fish. PETG is quite safe as a material, PET is common as a food safe plastic. SLA resins not really so much. Another note in this case is that PETG can be printed with quite thin walls and thus stay lightweight enough to float whereas resin prints are usually best printed solid and if not solid with thick walls.
Appreciate all the good comments/feedback. Best I can tell via link from @Devmani and similar sources, it’s entirely possible to do this with PETG but may involve some slicing tweaks. I’ve been able to create smaller water tight parts (< 1 oz volume) but struggling with larger sizes. I’ll continue to try different approaches. I’m sure it’s just a matter of trying a few different things. 
Thanks!
Hi all,
Just an update on creating a water tight print. I’ve found that a little post processing goes a long way.
On at least 2 parts, I sliced PETG with typical settings (and printed). And then afterward, I baked at ~200F for ~10 minutes. I’ve seen no obvious changes to the mechanical shape or strength of the part; however, the parts are now water tight. I suspect there is some optimization needed but this seems to be a good start.
I have more testing/prints ahead and I’ll report any different results.