Reproduce 3D Printed Models By Making Your Own Molds

Need fifty copies of that 3D printed whirligig you’re so proud of? It might be faster to just cast copies by using the 3D printed model to make a mold. [Micah] found himself in this situation and managed to cast one copy every 10-12 minutes using the mold seen above.

With the object in hand, you need to find a container which will fit the mold without too much waste. The bottom half of the mold is then filled with modeling clay, a few uniquely shaped objects to act as keys, and the model itself. After getting a good coating of release agent the rest of the mold is filled with a silicone rubber product which is sold for mold making. This creates one half of the mold. After it cures the clay and key objects are removed, everything is sprayed with the release agent, and the other half of the mold is poured.

Now your 3D object can be copied by pouring two-part resins in the to shiny new mold.

36 thoughts on “Reproduce 3D Printed Models By Making Your Own Molds

  1. This is something that geometric puzzle people were doing for a long time. For complete puzzles, it tends to be less work to just get the whole thing printed, but I’ve considered starting up printing masters and casting puzzles just because it hasn’t been done in a while.

  2. There’s a more ecconomical way to do it. I can really recommend mold max stroke and plasti paste II. Saves a lot of silicone. Also be aware that the silicone used in the picture (looks like oomoo, correct me if i’m wrong) is very fragile when used with object that has deep undercuts. If you want to produce a strong mold that can be used many times and stored then considder painting a layer of mold max 30, let it get sticky and then paint another thicker layer with a thickening agent in it. Then add a plasti paste II shim. This should give it the best hardness/durability and cost less :)

      1. Silicone caulk does not work well for moldmaking and casting. I’ve tried it, it’s a dead-end in my opinion. It’s easy enough to find relatively inexpensive materials designed for this purpose — it’s not worth cutting corners.

      2. Tried that once, when I was a kid. The stuff is designed to adhere to things — which means that if you can get it off your master, it will rip and leave bits in the nooks and crannies.

        (It pretty much ruined the cast-metal model truck wheel I was trying to duplicate; I never could get all the caulk out of it.)

    1. How does painting it on work for avoiding bubbles? One of my annoyances with poured molds is that there always seem to be tiny bubbles trapped in details on the surface, and I thought that a paint-on method might be able to avoid that.

      1. Vaccum or pressure solves that.

        Vacuum tends to be better, but pressure is easier. Buy one of those pressure paint pots, drop th mold in, turn on the compressor.

        Then do the same for the resin.

      2. Correct.

        If you paint the model with a very thin coat of silicone you can avoid bubbles. That’s what I do and it works :) You could also go with the high pour method; mix the silicone and start pouring from a high altitude. Make sure you only our a thin stream of silicone. This will often push the bubbles out of the silicone.

        Usually it depends on the viscosity of the silicone and some brands are better than others! :)

        A professional vacuum chamber is horribly expensive.

  3. Moldmaking is a GREAT skill to add to your roster, and it’s very easy to work with.

    Adding to Eirinn’s advice, I wanted to also recommend silicone putty, which is incredibly simple to work with. Consistency is about that of silly putty. Depending on the type, after mixing it up, you have 30 seconds to 5 minutes to squeeze it over your master before it hardens. Squeeze it over half, let it harden, spray it with mold release, and then squeeze on a second half and you have a two-part mold in just a few minutes of work.

    Mold making and casting is enormous fun — and you can do so many materials at home… candies and chocolates, plastics, wax candles, soap, even low-melting-point metals (I make my jewelry using silicone molds) and more.

    Anyway, it’s easy, fun, and quite inexpensive to get started on. I can’t recommend it enough.

    1. True! I think you’re referring to the Equinox product. I’ve heard that it’s an additive platinum cure product so it could be used with food (if the silicone is baked to seal it).

      I can’t relate to the cheap part, but I also buy silicone in 1kg containers ;)

      I also recommend using non-sulfur plasticine clay for claying in the objects. It doesn’t dry and can be re-used. I use the chavante modelling brand.

  4. Now your 3D object can be copied by pouring two-part resins in the to shiny new mold.

    Now your 3D object (with certain geometries only) can be copied by pouring two-part resins into the shiny new mold.


  5. Lego bricks work quite well for making mold boxes of exactly the right size. As a bonus, since the silicone sticks lightly but doesn’t get stuck, they’ll probably come out cleaner than they started!

    1. Yeah Lego works great. They’re not completely uniform though so you’ll have some silicone crawling into the crevasses. It’s not a problem, but I wouldn’t call it cleaner ;) Especially if you’re using mould release.

  6. Thick #84 or #107 rubber bands (Staples, 1/2″ or 5/8″ wide) work so much better than clamps to hold the two halves of the mold together. They spread the pressure more evenly and, most importantly, whatever you use, it will be all splayed with hardened resin as soon as you start casting in your mold. It’s a breeze to clean hardened resin from an elastic rubber band but a whole different story with a metal or plastic clamp.

    A rubber band is so cheap that you can even throw it away after a couple of uses and just get another one if you feel especially lazy in terms of cleaning.

    1. I’ve had bad experiences using rubber bands. They will always apply more pressure on the edges on the mould and deform it (depends on size and thikness of course). I would also go with the clamp method.

      EXCEPT: if a hard coat is used.

      1. It takes a little bit of practice to have the pressure distributed – slide a finger under the rubber band and move it around the mold – the rubber band goes back and sits much more evenly. It is more difficult to type it than to try it once – you’ll see what I mean.

        If the band is cutting into the corners, you just have a band that’s too short for the size of your mold – grab the next size up.

        I am very curious as to how you clean your clamps? I may be the clumsiest person in the world but even if you are EXTREMELY careful, I cannot think of a way to prevent the resin from splashing out every once in a while. How do you clean it when it hardens from a hard-surface object like the clamps? With the rubber band I just stretch the band and the clump of resin comes off (often flies off) by itself.


  7. I was actually looking into mold making for another project and was having trouble finding information on resins, like what type would be best for what (since some are designed for flexibility, some for clarity, etc). Does anyone have a good source of information and/or a good source of the resin itself?

    1. I use smooth-on products (google). They work great and they’re homogeneous (same result every time). If you’re from Europe then I can recommend KauPo (german reseller). I’m not sure about the US.

      Smooth Cast 300 has a pot-life (application time before hardening) of 3 minutes and a complete hardening of 10 minutes. Cures completely white and paints well. You could go with Smooth Cast 305 that has a post-life of 7min and a cure time of 30min :)

      Or are you in dire need of something translucent?

      1. +1 for Smooth-On ( )!

        I am perhaps slightly biased because I live about 20 min from them and therefore save a bundle on hazardous shipping but they are awesome in terms of the product choices and the tech support line is always open. I know people from the opposite Coast and all over the US that buy from them despite the shipping costs.

        I use Mold Max 30 (pink) for the mold and Smooth-Cast 300 for the resin when I need some translucency and Smooth-Cast 325 when I don’t (white base). Great stuff!


  8. Here’s how I make silicone molds.

    The paint pressure tank also works just fine for vacuum. It can easily hold a pressure differential* of 60 PSI so it has no problem withstanding normal atmospheric pressure on the outside VS a pretty good vacuum on the inside.

    *The pressure you see on the gauge is actually higher than the reading because it’s really showing the amount of pressure above the outside air pressure.

    What is the most expensive piece of equipment for this is a rotary vane vacuum pump capable of pulling near to 32″ mercury at high flow volume. In the years I’ve been making molds and castings I’ve found that vacuum is more bother than it’s worth. Using pressure is less expensive, faster and easier.

    1. I didn’t think more than 29.9x” (not sure about the decimals) mercury vacuum was theoretically possible. Anyhow, a Harbor Freight’s $70 small vac pump that pulls something like 29.5 is absolutely adequate for anything you may need in de-gassing.

      I hear what you are saying about the pressure chamber, I use the same setup (for pressure), but for vacuuming, although you can use the same chamber as for pressure, you really need to see what’s happening in there. Under low pressure the stuff really tends to boil over, spill and make a mess. I’m using a converted turkey fryer pot with a glass cover, all siliconed around to make a good seal between the pot and the cover. Works like a charm and holds the vacuum well.

      Another comment I wanted to make: don’t vacuum the mold material inside the mold walls, vacuum it in the mixing basket, then poor into the mold. It needs 45+ minutes to harden and only 7-10 for degassing, so you can use your pressure/vac chamber for something else most of the time you have to keep it closed and it’s easy to clean because it’s outside.

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