So I printed a couple of PLA capsules AND TPU gaskets the other day and was going to make t them water tight. Ok my problem is the top and bottom layers print as a sort of lattice mesh that lets water in. Layer lines are fine, it's just the to and bottoms it seems. Same ordeal with some brake bleeder stems I made from TPU, except it is they let air in and it won't hold a vacuum. Picture perfect print, except for the tops and bottoms.  Working on a planter now for momma, same deal.

I've tried everything I know how in Cura but just can't get the lines to weld together. My first thought is to just go to the hardware store and get some polyurethane spray and coat them. But, I'd much rather get this resolved in the printer.

Any ideas/suggestions?

clear lacquer, possibly model glue or some resins. Anything that will wick into the mesh and harden and become watertight, without delaminating or dimensionally distorting the print.

Good old Elmer's Glue might work OK - I haven't tried it. Perhaps rubber cement or crazy glue? Clear nail polish gelcote?

Try Hotter bed and increased extrusion for bottom


Try ironing and increased extrusion for the top

Can you take a picture? You should not have any gaps to see into the inside of the model. So you have something going south there.

Also, PLA is not waterproof in general and doesn't play well with most any chemicals. Do it right and use PETG, which is waterproof. It's actually pretty impervious to most chemicals, including hydrocarbons.

I used a few coats of acrylic primer on the inside surfaces of a HEPA filter housing used inline on a CPAP mask hose. TPU gaskets sealed the filter against the housing surfaces. Worked well enough to make any leakage undetectable.

If you print a single layer of a 20mmx20mm what does it look like?

It sounds like the first layer calibration needs some work, maybe try working through this process to see if it helps.

https://teachingtechyt.github.io/calibration.html

These prints are already sunk, so I'm gonna check my spray can options and will report back

Tried that. No luck

I've got a new roll of PETG up there that I haven't even tried yet. I need to just go ahead and make the switch. I've been reading here about printing it in preparation for the change over.

Sorry for the shitty pics, but here are a couple examples:





I'm trying a new profile to see if that helps. Might need to just slow things down. Have been using the Filament Friday "extra fast" profile which is speedy as hell but might be my problem. Planning on switching to 0.6mm nozzle based on your recommendations.

That's the direction I'm heading for these prints, at least. Glad to know it worked for you

Single layer cal is perfect. I'm thinking it is something in the profile. Just need to find what it is

Bromingo, you're suffering from severe underextrusion.

Run an EM calibration.

Use precise method.

Or...do the First Layer calibration and take a pic. That looks off.

One (or both) is off.

Your first layer is either significantly underextruded, or the nozzle is too far from the bed.  

The individual lines should not have any gap between them.

This is thruth

Switching back to an older profile fixed it. Now to find what I need to change in the faster one.

Extrusion was at 80% in the old, slow one and I even cranked it above 100% in the new, faster one. Bigger lines, same gaps. E-steps are dialed in correctly. There is just something in the faster profile that needs changing, or it is the speed itself.

I'll just go ahead and change to an 0.6mm nozzle and see if I still need more speed after that
Got some spray polyurethane to test out on the bad prints to see if that helps any.

What hotend are you running, and what is your volumetric flow rate? You may not be melting filament fast enough. That's the most likely explanation if it prints fine slow, and prints gaps when speeding up.

Make sure the slicer software knows which size nozzle you have.

Also, check first layer speeds. Most profiles slow them way down to ensure good adhesion and a clean first layer. So it may be something totally different messing with you if the difference is still on the first layer.

Huh? I've done a lot of chemical tests with PLA and found not much harms it besides removing the pigment. Acetone, alcohol, toluene, Tetrachloroethylene are the main ones that things I print in PLA come in contact with. Long term submersion in toluene and tetrachloroethylene make it kinda soft for a little while but it has to be total submersion for multiple days at a time. Splashes and cleaning have no real negative affect.


For the OP, good luck with water and air tight. I worked on designing a 3D printable diaphragm vacuum pump for a while. I found that I could not make it efficient with FSM printing and had to go to resin printing to do it. With a resin printed pump I can see as high as 15inhg of vacuum and I have one that has been used on a production line for almost a year now with zero issues. It gets exposed to toluene fumes.


The same pump with FDM printing is maybe 5inhg of vacuum.


You will have to over extrude to try to seal the inherent gaps created by FDM printing. Print hot, slow and over extrude a little to have the best chance. It can be done but isn't easy. I had issues with every material I tried to FDM print, even stuff like nylon.

Layer speed is a good idea. This is a "fast" profile and maybe the first layer is too fast. I'll have to check that out.

Hotend is a Microswiss. That shouldn't be the hold up, I won't think. All subsequent layers that aren't a "top" are fine.

Interesting. Thank you for the info.

Urethane spray seems to be working well. Soaks right into that mesh shit. May stop and get a bottle of the liquid to see if I can paint it in and keep the rest of the print clean.

The properties of PLA, and all other filament types, are well documented online. Water is a highly polarized organic solvent. PLA is a highly polarized organic compound. Like dissolves like, if you're familiar with organic chemistry. The relatively complex chains in PLA slows the process considerably, but long term use of PLA in wet environments simply isn't ideal.

You do you though.

Got the extra fast profile fixed.

Don't ask me what the issue was, because I don't know. Changed a bunch of shit, printed a couple of things, and everything is back to normal. Didn't do any tricks like increasing flow or extrusion. Didn't mess with the printer. Just good ol'fashioned fucking around on the computer trying to fix what I broke while fucking around.

Dunno. It worked. I'll take credit for my genius, though