3D Printing Watertight Containers

Most normal 3D prints are not watertight. There are a few reasons for this, but primarily it is little gaps between layers that is the culprit. [Mikey77] was determined to come up with a process for creating watertight objects and he shared his results.

The trick is to make the printer over extrude slightly. This causes the plastic from adjacent layers to merge together. He also makes sure there are several layers around the perimeters.

Of course, over extruding may not be good for your part’s dimensions. There are other techniques we’ve seen that work, too, like acetone smoothing ABS or using an epoxy coating to seal the print. Those are probably not going to keep your dimensions, either.

[Mikey77] talks a lot about food safety. Just remember, there’s more to food safety than just being watertight. We covered a lot of considerations about food safety and 3D printing. However, even if you just want to hold water for flowers or print an airway for a pick and place system, these techniques could be very handy even if not food safe.

Maybe with these kinds of techniques, we’ll see more 3D printed boats. Or perhaps a real submarine.

21 thoughts on “3D Printing Watertight Containers

  1. When it comes to the food safety of 3d printed objects I get the concern about additives in the filament. I also understand the concern that the ridges provide too much surface where bacteria can grow.

    Is the lead content of the print head really such a great concern though?

    Consider this. What if you were to print dishes, cups and utensils from food-safe filament through a brass nozzle continuously until the nozzle is worn out. For the sake of this scenario I am going to ignore the bacteria in the ridges issue.

    How much metal was carved away from the nozzle? It’s a very small amount isn’t it? And is that metal all lead? No, only a very small percentage of it is lead.

    So, of this tiny portion of a small quantity of metal which is lead that was eroded away are you going to consume it all? No. Some ended up in rafts, support material and failed prints. That which did make it into your printed goods should be more or less evenly spread throughout. That means most will be in the interior of the walls where it is encased by plastic. Only that which made it into a thin skin of the plastic’s surface will be available for you to potentially ingest.

    Are you going to consume all of the lead that makes it into that thin skin on the outside of your new eating utensils? Again, no way! Some might just stick to the plastic and remain there for the life of the item. Of the lead that does eventually come off much of it will not even end up in your food. Some will come off when it is washed. Some will come off when it is handled (some of which you might ingest but much of it you will not).

    How much lead would one actually ever ingest even if they ate every meal using plates, utensils and cups that were 3d printed through brass nozzles?

    Now I already hear some people saying.. no amount of lead is good and what about bio-accumulation? Ok, fair enough but consider this;

    Lead exists in nature too. Its in the rocks and the soil (which is broken down old rocks). Lets take a swim. I will imagine for a moment that there is such a thing as a lake with absolutely zero unnatural pollution. Maybe we are on another world or travel several centuries back in a time machine or something. Here’s a crystal clear, beautiful, clean lake. There are rocks and soil in the bottom. I bet some of them have some natural lead in them. How about that stream that feeds the lake? It winds around over all sorts of rocks and soil bringing with it whatever are the most soluble bits and dumps it into our lake where it is concentrated by the continuous flow plus evaporation. Surely there is lead in the lake!

    And yet we can swim in it with no ill effects. You probably even swallow a bit of the water by accident. For that matter, in this hypothetical non-industrial world where do you get your water from?

    And yet over billions of generations humans managed to evolve. We can’t be THAT sensitive to such minute quantities of lead!

    Don’t get me wrong. I’m not advocating for dumping leaded waste into our lakes and streams. I don’t support a return to leaded gasoline and paint. Certainly lead is nasty stuff we should avoid but you have to be reasonable about it. If you look for concentrations low enough it will be everywhere and you will have nowhere to go!

    1. Soil already contains something around 50 ppm of lead. Wheat nuts contain 25ppm of lead. I would bet money that your 3D printed plate contains less than that, and you’re not even eating it.

    2. “this tiny portion of a small quantity of metal which is lead”

      It’s not as tiny as you might first think. 3 to 5% or so in most “easy to machine” brass alloys.

      “over billions of generations humans managed to evolve”

      And billions of humans would have also died during that time. It’s clearly not something that is immediately harmful but it is incorrect to then assume that as a result of that, it is perfectly harmless. Especially when every single human in your example would have died. The question then becomes how many died as a hastened effect from this one source? There is no easy way to definitively state that but we still know that lead has a detrimental effect on most living organisms.

      Also, humans have not been alive for billions of generations either.

      There is radiation (and a number of other harmful things) in off the shelf bananas as another example. That’s still not great for you either.

      The other concern is, as you mentioned, bio-accumulation. A small amount of lead over a long time is still a big problem. At least the body can sort of repair radiation damage once the damage has occurred. Though we ingest radioactive things all the time. Again, the dose is the critical issue here but that’s a secondary point anyway.

      That all aside, the real issue here isn’t so much the lead (which can be mitigated by using other metals) but the ABS not being food safe. Epoxy coating it just covers the printed material in bisphenol A (BPA) which does little to render it food safe. If anything, that just makes it worse! Neat application but appropriately labeled as not food safe.

      1. Maybe a couple cubic milligrams of brass might be worn from your nozzle. Many brass alloys contain no lead, but even 3-5% of lead would correspond to about half a milligram. When spread over multiple kilograms of filament, that’s much less than even 1ppm, far below the levels found in soil naturally (50-400 ppm) or even things like potatoes or nuts (up to 25ppm. This is not a real concern.

        I agree ABS isn’t terribly food safe, though. It smells like death when you print it, the acetone makes it smell even worse. PLA is much better, although you have to anneal it before it can withstand higher temperatures. Porosity is a concern, there, but you can actually kill bacteria by boiling annealed PLA parts in water if you like (which is also a good way of annealing them).

        Food safe coatings is a good thing to invest in, I think.

      2. “Also, humans have not been alive for billions of generations either.”

        Nope! I didn’t mean to imply that they were though. I was talking about the transition from first-life to modern man and on through to ourselves. All the way along which our ancestors would have had greater amounts of lead to worry about than what one might get from their printer nozzle.

      3. “It’s not as tiny as you might first think. 3 to 5% or so in most “easy to machine” brass alloys.”

        Sure, 3-5% isn’t tiny if you intend to directly consume something that is 3-5% lead. That’s not happening here. Look at all the other things I wrote. I’m still thinking that the amount of lead a person would actually consume from this would be below natural background levels anyway.

        1. The lead directly from the nozzle into each of the parts being printed is not much though brass parts can contain a surprisingly large amount of brass and were for a long time considered to be food grade, oddly enough.

          It still shouldn’t be a leaded part if you are going to use it with food. But that’s not really the biggest concern here anyway. ABS is not an appropriate food safe material irregardless of how you process it. I guess you could in theory coat it in a material that is but it would need to actually adhere to the ABS and that material would need to also be food grade.

    3. why the huge rant about lead?nowhere in the article is lead even mentioned since this is only about making tight containers. also as you guessed right in your first sentence the biggest worries about filaments is chemical leaching from additives and leftover polymerization reactant depending on the plastic. bacterial film could be an issue but I’m pretty sure that if you post process your print to make them smooth the risk should be minimal.

      1. “why the huge rant about lead?”
        Cause I felt like it. And I can.
        And because I think ‘making’ is important and people are very food-motivated so discouraging them unnecessarily is bad.

        “nowhere in the article is lead even mentioned”
        Ah… but that’s where you went wrong. I believe you are referring to the summary and didn’t actually read the article did you? Hint… you have to actually click the link. Here’s an on-page hint for you though that you don’t even need to click for… “[Mikey77] talks a lot about food safety. Just remember, there’s more to food safety than just being watertight”

        “I’m pretty sure that if you post process your print to make them smooth the risk should be minimal.”
        Perhaps but that’s cheating! Why? well.. I could just cast the whole thing out of lead or even something more poisonous and still say the same thing. All you have to do is coat it in something that is food safe and durable.
        That’s actually what is usually recommended if you want to print a food safe item and use it more than once. Cover it in a layer some sort of food-safe coating. Others do suggest sanding but the sandpaper itself leaves scratches that even if we can’t see them are more than big enough to make a nice comfy home for bacteria.

        1. dude can you even read? i don’t even disagree with you on the principle of it but in THIS article its all about printing watertight objects the word lead doesn’t even pop up a single time ( go ahead do a search on this page for lead) the article you referred to is linked but its a different article all together.
          i said make it smooth i dint say coat it in whatever.

    4. I think you are about due from a visit for the Safety Police!

      This sort of irresponsible, dangerous, “should be illegal”, rational reason is simply not allowed. How DARE you attempt to minimize risk with the use of science or logic?
      Any safety threat should result in am immediate and irrational overreaction with lots of condescension, passive aggressive lecturing and general finger waggling towards anyone not also defecating themselves in fear.

      Consider yourself waggled, buddy! Consider yourself waggled.

      What I find amusing about the Safety Police is quite often they are bananas about some obscure tiny risk (e.g. germs) and yet by the looks of their diet should be more worried about their (almost guaranteed) impending heart attack, diabetes and/or stomach cancer from all the crap they eat.

      A bit like when I read Trump was a “germaphobe” yet apparently likes to sleep with porn stars (yuck much?!) and sit in bed stuffing his obese face with McDs.


      (NB: this was not a political rant – just a pop-reference to a very well-known example)

    5. I’m inclined to agree, mostly with the idea of bacterial buildup between layers
      It would be smart to smooth your print significantly or use ABS and acetone smoothing
      PLA will also breakdown with some substances over time and is recommend only for disposable products

      But it’s a good bit of insight on how to make water tight thin products for uses like making molds or funnels or tubes or whatnot

  2. What kind of coatings/epoxies are food safe to seal 3D printed parts for food contact? I would not want to print a coffee/tea cup (probably a bad idea outside of the contamination problems when mixing heat and thermoplastics). But maybe a nice decorative bowl to present some fruits, or let’s say a cookie cutter or something along those lines.

    1. In the US: GE Silicone 1 (not 2) is one of them. The Amazing Clear Cast is another. Those are the easy to get ones if you want the FDA (500?) rule.

      A lot of materials aren’t rated as ‘food safe’ but are used that way. We are very, very careful in the US (at least the FDA is) about what’s called food safe. Plain PLA can be rated as food safe (Yeah, Coffee/Tea… would be a problem), along with PET, and others.

    2. I’ve done cookie cutters in PLA, but admittedly never tried to clean them afterwards; just threw them away. If I ever want to use that particular cutter again (they’ve all been for special or very specific occasions), I can always just print them again.

  3. Had not realized that “watertight” was still an issue to accomplish with 3D printing. Nowhere near ready for “Tea. Earl Grey. Hot.”.

    This is still just a hobby. But to be fair by comparison, HAMs still aren’t anywhere near done either.

    1. I modeled and printed a custom mug on my little Anet A8. Double-walled ABS, brushed with acetone and left to dry for several days, repeat 3 times.

      Water-tight, held up well against hot Earl Grey tea, and was well insulated.

      It was fragile, though, and after being dropped it developed a hairline crack on the inner wall I couldn’t seem to seal reliably. I imagine thicker outer layers and some infill would improve that, though.

  4. I encountered this when making patterned cups .stl files I found that use continious z motion. the cup prints in a continious spiral of .5mm extrusion, dialing up the extrusion rate in matter control allowed better watertightness in the base, especially for the first base layers adhering to the beginning of the spiral exterior. A well squished first layer is always good for bed adhesion but essential for sealing against leaks. Finally if there are leaks, it’s not a total waste, use the filiment in the dremel trick to -plastic-weld closed any remaining gaps.

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