Use Smooth Sill silicone to get more from your 3d Prints

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Use Smooth Sill silicone to get more from your 3d Prints
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Make silicone molds for fun and profit

This is one of those things that’s obvious to people that know about the topic and not so obvious to everyone else. Learning to use Smooth sill silicone can be just as rewarding as learning to use a 3d printer.Before I go on I’d like to give a little info on my background to help with the context. Before the housing market crashed I worked in fiberglassing and mold making. I learned in a shipyard making composite boat hulls and took a full-time job working in a bathroom fixture factory making everything from hot tubs to basic showers. It sounds a lot simpler than the job really is but the basics are as follows. You create a model that model is turned into a mold and then you make a part from that mold using in my case chopped fiberglass or carbon fiber mat. For our purposes, we will be using a 3d printer or CNC to make a buck or plug. We will prep the plug which is easy with silicone and make a mold from that plug. After that, because we are using a food safe mold with smooth sill we can make anything in it. If you use chemicals in it like resins it stops being food grade. Remember Mr. Yuk.

Why make molds when I have a 3d printer/CNC?

Here is that question Some of you will ask. Yes, you can print as many of the objects as you like but not as fast as I can replicate one. There isn’t a CNC or 3d printer made that can replicate a part as fast as a mold can. 3d printing shines in the ability to make a one off part very quickly but it fails when it comes time to mass produce something. Maybe it’s because I worked in the field but I don’t understand this trend to build printer farms to make lots of parts. I’ll use 3d printers to make my point. Most low-end systems use 3d printed parts. Most of these parts are not very complex. You could crank out molded parts at 3 times the rate using blown molds or injection. I’m getting above everyone’s head I know but someone will understand. They will argue that cost of tooling is expensive but somehow 50 printers aren’t. This is a short term gain long term loss. Operating hours and maintenance will cost so much more. Ok, so the business lesson is over.

Why should the home gamer make molds?

Same reason but more. I could list all the advantages of 3d printing for everyone but that would be a whole nother article. Really it comes down to getting more from your prints. Raise your hands if you printed a benchy or a Marvin. Come on don’t be shy. Look We are all friends here tell the truth. You in the racing chair I see 3 on your desk get your hand up. Ok now raise your hand if you have an edible Benchy or Marvin. Mr. Racing chair put your hand down. No one likes a smartass. None of you thought to make an edible version and that’s ok we will fix that. Desk toys are all well and good but after a while, they just collect dust. Learning to make molds can add much more to your hobby. With silicone, it’s easy because you don’t need to mess with things like release agents. The only thing silicone sticks to is silicone.

Some of you don’t want to make food molds.

Maybe you are a part maker and don’t just play with your 3d printer. In that case, most of you already know about mold making. On the off chance, you haven’t thought of it. a fiberglass or carbon fiber part will always be stronger than a 3d printed part. I don’t want to hear about printers that make carbon fiber. They aren’t in the budget for a home gamer. Molds are, though. In the mold case, rigid molds would be better for a lot of it but soft molds can get you pretty far. I’m not going to make a full write-up in this article but if enough of you are interested I could make a second more detailed one on the subject. Suffice to say the process is about the same.  The result is a mold that can be used to make parts or objects faster and more consistent than a 3d printer.

Smooth sill 940

This is my favorite silicone to use primarily because it’s not toxic in any way. If you have kids you will understand why this is important. I also like it because I can buy small sample sizes from places like amazon. I don’t live close to any retailers that sell silicone locally and buying 10 gallons of silicone to make some ice cube molds is crazy. It’s a simple 2 part compound with easy to follow directions for anyone not used to working with it. When used it produces quality molds with almost no effort. All you need is some dixie cups a water tight box just larger than the plug and glue stick or hot glue gun to keep your part submerged.

How to use smooth sill.


There are only a couple steps that can trip up a first timer with silicone or really any other liquid molding agent. First get the mold prepped. Make sure the box is water tight. Make sure you glue down your part. When you mix the silicone and the activator go slow you want to avoid making bubbles. When you pour the silicone do it from as high as you can. Doing this will help pop any bubbles that formed. You can invest in a vacuum chamber down the line if you plan to make lots of molds but for the first few times, it’s not needed. You might just have to do a little cleanup later.

The first crossroad is making a single cast and cutting the part out or making a 2 part mold. For the beginner, I suggest making a single pour and cutting the mold in half after it cures. When you do cut it in half don’t just make straight cuts, though. Cut some zig zags or 90-degree angles so that when you put the mold back together it is straight or “registered”.

The second crossroad is filling the mold. Let’s say we want to make a chocolate Marvin. Don’t just pour all the chocolate in at once. Put in just enough to coat the inside of the mold Let that set up a little then fill the mold slowly. If you are working with Resins it’s the came idea only smellier and less edible. Demolding is easy, simply pull it apart. because next to nothing sticks to silicone the part will just pop out of the mold. Rince and repeat as many times as you like make a box of chocolate Marvin’s and impress your friends.

King of Random tutorials.

He does a great job of showing everything I explained above and along the way he makes the same mistakes I explained above. between his videos and my summary above you should be able to start making molds in no time at all.

Lego Gummies


If you go to his channel you will find a lot more videos of him working with silicone and mold making.



I’ll let you in on a little secret. You don’t need a CNC or 3d printer. This is one of the skills that when mastered can reproduce many parts for many different things. I have molds for everything from car parts to body parts. Get your mind out of the gutter Halloween is a lot more fun when you can fake body parts. Your child becomes really popular when they show up with edible gummy hands for their Halloween party. You can imagine April fools being a lot of fun as well. I have a hell of a prank planned for my Girlfriend this year.


Get The Smooth Sill 2 lb kit


For more tips like this check out my last post on 5 kits to get more from your 3D Printer

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  1. [email protected] says

    I love the Pokeball. There is so much you can do with these.

  2. jvastine says

    Great article! I would like you to take this further to open people up to the possibilities. You could develop a series that covers hard molds, working with fiberglass, carbon fiber, kevlar, and other materials in the molding process. Even getting into vacuum forming, injection molding, and other processes that could be scaled down to a desktop or benchtop would be great. This would be a great resource that would help and benefit many. In fact, I have a youth program where this information would be an invaluable resource. Thanks for your willingness to share your knowledge and experience with others as I truly appreciate the valuable treasure and gift that is. This is a trait I try to instill in the youth for the world would be a far better place if we all freely shared and helped one another. Anyway, I look forward to seeing more from you.

    1. Nathan Cox says

      Thanks, I will be making more on this subject in the near future. I’m glad to see that I can help people.

      1. jvastine says

        Great! I know that the information you share will benefit the youth participating in my program in many ways. The most important of which is to offer them a brighter future building a cottage or grassroots business. At the present time, the majority of those in the program are from the inner city where there is no opportunity and the public education system is failing them as many of the teens read and write at around the third-grade level. There is no vocational training and going to college or a vocational training center is out of their reach. This is the fundamental reason why crime, gangs, and drugs are so prevalent in the inner cities. However, we are slowly but surely changing that paradigm and your contribution will help. Plus since info on the web has a worldwide audience, those things we share will benefit people all over the globe and continue to do so long after we are gone. Thus your efforts will impact the lives of others far beyond what you will ever know or realize. You and the information that you share are vitally important! Thank you for your contribution, it is greatly appreciated.

  3. mperkins37 says

    Cool stuff, thanks for sharing, lego gummies… yum

  4. Christopher says

    I liked this post so much, I had to tweet it again.

    1. Nathan Cox says

      Thanks Glad you liked it.

  5. aDopeDwarf says

    Great build up, please do follow up with what you know. Knowledge is power. I like the Halloween ideas. Clever indeed. Waiting patiently for next article. Thank you for you time.

  6. Joel says

    Awesome article!

  7. cody says


  8. neo777 says

    Thank you for this!

  9. Richard Bynum says

    Nice article. I used to work on plastic injection molding machines back in 96′. I only worked there for about 7 or 8 months before they had layoffs but I got to learn a lot about it. The molds they used were VERY expensive and had to be handled with care. They also had to be carried on a forklift because they were really heavy!! I had to drive some around the plant on the end of the forks and my heart was about to jump out of my chest!! Now that I’m into 3D printing I would love to add to it by making molds to come up with some nice stuff! It sounds fun! And easy! Just make something on the 3D printer to be the mold and you will have it anytime you want/need to go back and make it!

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