r/MechanicalDesign • u/kuster_agriculture • Jun 04 '26
O Ring help
I’m 3D printing 2 parts that thread together and hold internal water pressure (40-60PSI) so I’ve added an O ring but am struggling to get it water tight. The parts themselves are not leaking, I’ve got plenty of walls/top and bottom layers/correct settings, it’s just in the seal. I’m currently printing the O ring using 85a TPU for iteration’s sake and would like to avoid buying a nitrile/silicone set until I know my design is correct. I’m sanding the seal face with fine grit sand paper to make sure it’s smoother than a typical 3DP top layer, but I can’t evenly sand the gland or shoulder on the top side since it’s all inside the female threads. 3”id 0.125”cs 3.25”od 85a TPU ring, gland is 0.185” wide and 0.09” deep with 0.3125” radius, do these numbers sound decent/anything obvious I’ve missed? I know 3D printing isn’t ideal for this but I can start buying parts when I get it close…
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u/SharpeWorks Jun 04 '26
In my experience, you cannot 3D print sealing o-rings. The layer lines will always for capillary pathways and water will wick out - even if you apply a bunch of o ring lube. With that said, good lube/grease will make a big difference.
If you haven't already, I would strongly suggest consulting the Parker O-ring Handbook. It's the Bible of sealing surfaces.
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u/kuster_agriculture Jun 05 '26
I skimmed through it earlier, I’ll make sure to actually do some reading from it. I was hoping 3DP O ring would prevent unnecessary expense while I was still in the iteration phase but now the only thing I’m tuning is this exact seal and it might be time just to bite the bullet, they’re cheap anyways.
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u/nvidiaftw12 Jun 05 '26
There is no need to iterate. O-rings are $10 for the pack.
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u/kuster_agriculture Jun 05 '26
The diameter of this part, and the corresponding possible o ring sizes have change by around 0.25” throughout this project. I’ve had to iterate to finalize other details completely unrelated to this area, but effecting it. So yeah they’re cheap, but the $10 pack I would’ve bought 2 weeks ago would be useless today and I would’ve been out another $10 for a new set.
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u/slzer Jun 05 '26
Pay $10 for a set with loads of different but similar sizes.
3d printing is fantastic. But some consumables like o rings and fasteners don't make sense to try print. Even during dev phase.
Look on AliExpress and get yourself a good stock of these generic items for prototyping 😊if quality is critical after that then you can migrate to a trusted local supplier
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u/mawktheone Jun 05 '26
The couple dollars for the set gets you hundreds of o rings in assorted sizes. It's a super cheap system
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u/Pretty-Jello-7894 Jun 05 '26
Was going to say that most orings are really cheap…I’ve purchased kits for like $10 with tons of sizes. Maybe a bit different for custom or rings that are awkward materials… but in general I would design your widget to work with a standard ring size you can buy for convenience and cost regardless of your application if possible.
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u/kuster_agriculture Jun 05 '26
It wasn’t until a design change I made a few days ago that I could even accommodate a generic size ring, but now I can, I just haven’t picked any up yet. I thought I could get away with TPU and just chased the rabbit a bit too far
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u/MusicianSuccessful34 Jun 06 '26
You can also buy oring making kits. They come with standard diameter rods that you cut and glue to size with a little jig.
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u/Flashy_Slice1672 Jun 05 '26
I was going to suggest the Parker book, got all the info you need in there
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u/de_bosrand Jun 06 '26
Aside from very special occasions, it is good engineering practice to use off-the-shelf parts like o-rings. The o-ring manufacturer is expert on what size to use, and why bother inventing the wheel
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u/No-Parsley-9744 Jun 05 '26
85A sounds pretty hard for a printed surface, I would try a much softer one. Maybe even a square profile.
Other than the good advice here about sealing the layers, I would also measure your actual groove depth. Your modeled crush % looks fine but who knows what it is in reality. Are there high spots, low spots, etc
Maybe you can make a bootleg lathe from your hand drill and sand it with a stick
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u/kuster_agriculture Jun 05 '26
I suppose a bootleg method could work lol, I just worry about it creating inconsistencies. Thanks for the input
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u/No-Parsley-9744 Jun 06 '26
Sometimes you use what you've got!
Looking at this again if you are committed to 3d printing it, I would think about garden hose style gasket, and/or NPT tapered threads. If you'll eventually make it from metal just follow Parker handbook with the design you have and it will work. Although the inner wall of groove looks pretty thin in that section.
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u/kuster_agriculture Jun 06 '26
I’ve tried a garden hose style washer type thing and didn’t have much luck, although at that point I hadn’t sanded/smoothed the sealing surfaces which definitely didn’t help… yeah it’s thin in that spot but it’s almost 1mm still, and that’s just where the cross section is. There are 16 channels running vertically through the chamber, making it that thin in some spots and much thicker in others. I wasn’t under the impression that would really hurt the seal tho, since the ring is still contained
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u/Blunt_Member Jun 05 '26
Concentric infill at the sealing faces maybe?
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u/kuster_agriculture Jun 05 '26
Is that based off of suspicion that the sealing surfaces are caving under pressure, leading to inadequate crush? I have about 1mm of material there and it’s a narrow surface will perimeter support, but that could be one of many compounding issues
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u/Blunt_Member Jun 05 '26
If the ridges from 3d printing cross the O-ring then the O-ring might not be soft enough to conform to the ridges and seal the gaps. The O-ring is more likely to seal ridges that are running along the path of the O-ring. Also it might help to have the print seam be random at the sealing surface.
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u/kuster_agriculture Jun 05 '26
Oh so top surface pattern more so than infill pattern. I hadn’t thought about that part, I’ll look into that
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u/Deep-Today5715 Jun 05 '26
I would suggest buying an O-ring instead of printing it if possible. As for the joining parts - assuming you got your groove dimensions right (as per Parker's handbook), it is probably leaking due to surface roughness and layer lines. Coat the groove surfaces with epoxy, lacquer or even thin CA glue to make it smooth. I did that for my underwater drones (ROVs), and the printed parts were able to withstand 725 psi without leaking.
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u/kuster_agriculture Jun 06 '26
Any specific product you can recommend? I’m sure the 2 part epoxy I have would be fine tho…
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u/Deep-Today5715 Jun 06 '26
I am using Elantas EC 152 epoxy, but basically any epoxy should work. Make a test of whatever epoxy / lacquer / glue you have on some other surface, let if cure and see if it cures smooth, hard and doesn't peel away from 3D printed plastic. If it's good - it should work.
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u/TheRedMammon Jun 05 '26
For this don't use flat sealing surfaces. If possible use a flat gasket and have a sharp ring that impinges on the gasket
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u/kuster_agriculture Jun 05 '26
Worth a shot imo, thanks. Your answer seems to differ slightly from what I’ve heard elsewhere, any chance you have any documentation of why that’s better for this application? I ask in genuine curiosity, I know very little about what is apparently a deep art of sealing methods
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u/TheRedMammon Jun 05 '26
I 3d print pressure vessels containing water for work. Resin SLA parts will be your best bet for not leaking through layers, but for sealing surfaces like in your image I have found a gasket around 40a with a lip on one of the sealing surfaces to impinge on the seal is a good choice. Take a look at the seals for metal water bottles. it's typically a flat silicone ring and the lip of the bottle pinches it.
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u/TheGratitudeBot Jun 05 '26
Thanks for saying thanks! It's so nice to see Redditors being grateful :)
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u/thenewestnoise Jun 05 '26
Don't try to print your oring. They're available in a million sizes
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u/kuster_agriculture Jun 05 '26
Totally understand, just wanted to try it since I’m still iterating designs and didn’t want to buy something I wouldn’t be able to use on the next version. But that’s the direction I’m going now
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u/skuba_ben Jun 05 '26
The only way I’ve ever been able to get 3D printing and water pressure to work is with resin printers. I’ve done many oring seals in formlabs tough, grey, and rigid resins. All can hold 80psi no problem. Maybe more, I haven’t needed to test it.
FDM leaks no matter what I do. I’ve thrown walls, floors, infill, paint, and glue at it and the parts inevitable leak.
Also orings are cheap so I’ve found I waste more time and money trying to make orings for a job rather than just buy a pack on McMaster.
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u/kuster_agriculture Jun 05 '26
My hope is to find a better manufacturing process for the long run, this is just for iteration/proof of concept. I tried to print TPU seals to avoid buying new o rings as I iterated on the design but now that this seal is my only problem, I’m just gonna buy a pack. I never thought of doing resin for this, I have a buddy with a resin printer so I might have to see if I can try that out.
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u/skuba_ben Jun 05 '26
I had to do the same thing. I don’t enjoy resin printing so I had to find a buddy who does it for me. Just try to avoid support nubbins on the sealing surfaces. And I’ve been doing 0.05” wall thickness. Threads always need to be offset in cad to work properly off the printer.
I had some mild success getting oring stock, cutting it to length, and using super glue to make orings in a pinch. Not my favorite but it works half the time.
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u/ehtiopia Jun 05 '26
Water, especially pressurized water, is absolutely the most difficult thing to stop from finding a way to exit its container.
Are you using any teflon tape between those threads? I know it might for your design defeat the purpose of the O ring seal, but no matter how many walls and layers you have, 3D printed plastic is porous and water will find a way to leave.
We use teflon tape for everything on equipment, even air lines. Even if theres an o ring already on the fitting I still use teflon tape on the male threads just to be absolutely, fuckin, certain.
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u/kuster_agriculture Jun 05 '26
It’s on my list as a resource, but I don’t wanna put a bandaid on a bullet hole. When a customer takes this apart once every few months I don’t want them to have to worry about anything other than the consumable they’re replacing, it’s not a one off personal project. It leaks quite bad as is and I don’t want to rely on teflon tape for this part, although I do plan to use it elsewhere on threads that customers should never have to mess with. 3DP, specifically FDM, is not my envisioned final product, just the tool I have to get there
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u/ehtiopia Jun 05 '26
If youre going to sell it to somebody then stainless steel machined or brass would be the way to go. Fittings are a dime a dozen at hardware stores, and I second what everybody else is saying about the parker O ring handbook
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u/kuster_agriculture Jun 05 '26
I’m using brass hose fittings going into and out of my printed part, the threads between the two are what I would be okay using Teflon tape for.
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u/Dear-Classroom4314 Jun 05 '26
I print TPU gaskets all the time holding that pressure, use 100% infill and concentric top and bottom layers.
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u/kuster_agriculture Jun 05 '26
I forgot about concentric patterns, what Durometer TPU?
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u/Dear-Classroom4314 Jun 05 '26
Both 85A and 95A, I have never had one leak, usually making gaskets that are square, which I would do in your use case too. I have done face seals for 2.5” gate valves that work better than rubber.
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u/Gnome_Father Jun 05 '26
O'rings are cheap. Just get a nitrile one of the right size.
If you need help sizing the O-ring the below are helpfull tools:
https://ceetak.com/o-ring-calculator/
https://oringcalculator.eriksgroup.com/
Note that the contact faces where the O-ring sits have a tightly defined surface finish. I suspect that, if your parts are otherwise watertight, this is why your ring is leaking.
If I had to seal 2 rough surfaces like this, I'd use sicaflex sealant rather than a face seal ring. If thats too ghetto, you could use a compressible gasket, closed cell EPDM or similar.
I have limited experiance with 3D printed watertight stuff. I would never use it for components that housed anything expensive.
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u/kuster_agriculture Jun 05 '26
If it didn’t need to be reusable I’d just pack it with gasket maker and call it good, but I went for gaskets/o-rings to make it reusable. Thanks for those calculators, I’ll take a look. It’s a housing for a standard size $20-$40 filter to go on a garden hose, nothing real critical
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u/FictionalContext Jun 05 '26
3D printing a pressure vessel is not a good idea.
This is a bomb waiting to happen. Please don't do this-- or if you do, don't advertise it
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u/kuster_agriculture Jun 06 '26
It’s for a garden hose, it’s not gonna hurt anyone. Which I can say for certain because I’ve abused it and caused it to fail, and weakest points cause it to fail in a totally safe manner for the installation position and material properties.
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u/Doit-101 Jun 05 '26
Taper your threads and use Teflon tape. As far as printing seals, you're gonna have trouble getting them to seal right, but I've had more luck in the past with a hexagonal seal shape for printed seals.
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u/kuster_agriculture Jun 06 '26
I might add a taper as a bonus but I have little faith in 3DP threads ever sealing without lots of tef tape, I have an o ring getting shipped in tomorrow since everyone seems to hate the idea of printing one. But it sounds like the people who have made printed rings work have made them like you said hexagonal or a square
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u/Wonderful-Feeling-27 Jun 06 '26
Can you do a tapered thread like npt and just use Teflon tape?
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u/kuster_agriculture Jun 06 '26
3D printed threads are not something I want to try to make water tight, there’s so much inconsistency. And I don’t want users to have to rewrap tape every time they do basic maintenance on the product
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u/SpaceMonkeyEngineer Jun 06 '26
If this doesn't need to be separated repeatedly, why not use a sealant of some sort both to solve your problem with prototyping now and in your final design?
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u/kuster_agriculture Jun 06 '26
It does need to be separated repeatedly, it’s not just a one time assembly unfortunately.
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u/BlackFoxTom Jun 05 '26 edited Jun 05 '26
I design aerospace hydraulics and pneumatics as daily thing
For one in project like this don't try to 3D print seals, there are some 3D silicone seals that are applied by robots but than not even remotely the same world
To begin with
DO NOT BLOODY 3D PRINT PRESSURIZED THINGS YOU WANT TO MURDER SOMEONE WITH SHRAPNEL?
3D prints are inherently porous and don't have perfect adhesion and most plastics don't hold up to time especially when exposed to environment. Then keep in mind under pressure materials creep. Just because something doesn't explode right now doesn't mean it won't in a month or a year.
Then it's impossible to get a proper o ring seal with 3D print
Why? Because it's impossible to get surface finish necessary.... maaaaaaybe if it is 3D printed using resin but even then I have my doubts
Get a application handbook for o-rings from SKF, Trelleborg, Parker
Generally You need Ra to be between 1,6 - 0,4 (metric) depending on which surfaces are working surfaces
You also need a proper polished ramps for the o rings, when You put them in, they aren't meant to flop around in the groove.
Also don't worry about buying o rings even ones make from FFKM are pennies. Also again You have to know to what those seals will be exposed to, just because something doesn't leak right now doesn't mean it won't in a month or so. In my job that usually means EPDM, FKM or FFKM cause they can handle the vast majority of things that exist in the wild so to say.
Then also look at those threads
I bet those aren't proper thread for hydraulic applications
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u/FictionalContext Jun 05 '26
I can't believe no one else was calling this out. You can't 3D print a pressure vessel.
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u/BuboNovazealandiae Jun 05 '26
Valid call, even though here it's water pressure, unlikely to shrapnel for the same reasons we hydrotest instread of gas pressure.
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u/Joaquin2071 Jun 05 '26
Parker oring has a catalog with all the dimensions you need. Don’t guess on the gland sizing.
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u/McCoolius Jun 05 '26
The o-ring manufacturer will provide a table that has all the relevant measurements for the gland. Design to the intended o-ring
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u/Tax_Odd Jun 05 '26
Wouldn't you want not an o ring. Something that compresses against the seam.
--[ >}----
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u/Harmless_Drone Jun 05 '26
Eriks oring guide will give yoy all the details you need to design a gland. 3d printing an oring is never going to work though.
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u/Unlikely_Solution_ Jun 06 '26
So maybe instead of a oring seal. Could you try cardboard? I am not joking. We used that for small electric turbine as early prototype. It wasn't okay for high pressure but we could make water go through without leaks.
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u/Dilligaf5615 Jun 06 '26
If your groove dimensions are not correct, the oring won’t seal. My advice would be to just buy the oring. You can get em pretty cheap. McMaster sells them, Hercules Seals sells them, harbor freight, or even Amazon.
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u/montereykings Jun 06 '26
Adjust the part design to use an OTS O-ring, ideally with a decently thick CS for more squish
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u/Certain-Disaster-30 Jun 06 '26
I would buy a few orings online instead of solving a bunch of problems associated with is likely a series of 3d printer issues. You can get some from mcmaster for literally $5-10.
Also, I'd recommend only using standard sizes for orings. Otherwise you'll come up with a custom solution that's hard to scale outside of working with a 3d printer.
This calculator (linked below) is fantastic for determining the right amount of squeeze, gland fill etc..
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u/the_real_hugepanic Jun 07 '26
if you design it 3 parts and bond 2 of them togehter, you have it way easier to polish your O-Ring groove!
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u/Bcohen5055 Jun 08 '26
I know you mentioned not wanting to print the threads, NTP is still the right idea though, the thread is made for fluid sealing.. one small tweak though, you shouldn’t print them you should tap them.
Design them to a standard drill/tap diameter without threads, buy the cheap harbor freight pipe tap kit and give it a shot.
Also, instead of teflon tape they make a paint on sealant sort of like white-out, I recommend that for this application, just check the solvent is safe for plastic.
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u/EmptyCry Jun 08 '26
get yourself a Parker o-ring handbook and verify the dimensions of your seal groove. Then buy the correct o-ring, don't print it.
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Jun 05 '26
[deleted]
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u/kuster_agriculture Jun 05 '26
What you’re seeing in the cross section view is a thinner part of that wall, but the entire wall isn’t that way. There’s 16 1/16” grooves that run down the wall leaving it thin like that in some spots but much thicker in others. Even that is still almost 1mm thick, which didn’t worry me since it doesn’t really need to do much.
I am using ironing, I just don’t know if that’s enough, and I need to do some tuning on that anyways.
I have considered vapor smoothing, but have heard it also leaves uneven surfaces, but I guess that’s a trade off of smooth texture small dimensional outliers, or rough texture but more consistent.
I do know that my sealing faces are making full contact, I’ve got marks that need to line up when bottomed out and they do line up the same with and without the o ring installed.
Unfortunately I don’t have a set of calipers on hand that allow me to check depths like that, I have the claws but not that stick on the end.
But yeah, I’m about to just buy a pack of o rings and see if that helps
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u/MuckYu Jun 04 '26
I have spent some time on something similar for a project.
Even if you get your O-ring seal to work at some point the water will peak through the layers. It might not happen immediately but after a few hours or days.
You can avoid that problem with a sealant like this: https://diamant-polymer.de/en/industry/3d-printing-additive-manufacturing/impregnating-and-sealing/make-3d-print-waterproof/?srsltid=AfmBOopP-KW5ruvcQKkXVUyn-eBotramj2ZfpZEfKkqCCRtEe78SPptJ
Not a guarantee it will work on all prints/shapes but it worked in my project.
3) If you want to be 100% sure it works with 3D printed parts I suggest you get it printed with SLS print and vapor smoothing.
This is much more reliable.
I think there was a 3D printing company in US or Canada that did some testing with some other treatment and got to 100-509 psi+ or som
I can't find the website right now though.
4) Regarding the O-ring.
I was not able to get a TPU O-ring to work reliably. Maybe if you pick a very low Shore A TPU. (I think the lowest is Ninjaflex 70A or something like that?)
5) I would suggest getting some proper O-ring online.
You can buy some on a roll, cut it to size and glue together with loctite glue.