High-Quality Finishing – Part 2

Welcome to part two of this series on how to give your 3D printed parts a high quality finish. In Part One we went through how the prop was designed, printed, and how we sanded and painted it to get the perfect surface finish before adding the silver paint and weathering to round it all off. In this blog we will show you how you you can take a 3D printed part and use it to make a Silicone mould and cast replicas of that master. Using this technique is great in order to create exact copies of the same model.

This tutorial leads perfectly from the previous part as all the steps taken up until we painted the silver is the same. We shall start off from a well painted and sanded master.

We used some 3mm foam board to build a mould box. This was glued with a hot glue gun, we then used a putty to create a temporary base. We placed the master in the clay and smoothed it off to make our split line.

Once the clay was smooth we used the back of a paint brush to jab shallow holes in the surface. These are registration marks and help the two mould halves to fit together to create a good seal.

Now the fun begins. We used a smooth on mould star silicone. This was mixed at a 50/50 ratio. We used an old paintbrush to gently pat the silicone on the master. This helps out to get the perfect mould surface and removes any bubbles on the surface. We then poured the rest in and let it set.

Once it was set we tore away the mould box and removed the clay. This revealed one mould half. We then cleaned it up a little and then begun building the last mould box. We used a glue gun to do this again. Before pouring the other half it’s important to spray on a mould release. Without this when you pour the second round of silicone in this will fuse to the previous silicone pour. With the mould release it prevents them from fusing.

We used the same ratio and same technique as the first pour on this. Once it cured we removed the mould box and split the two halfs. This came apart really well and revealed our two mould halves. We then used a sharp knife to cut our pouring channel.

Unfortunately this wasn’t large enough during our first resin pour. To solve this we cut a larger hole. And tried again. We used an aluminum powder to coat the surface of the mould and held the two halves together using two boards of foam board and elastic bands.

This didn’t work out too well the second time as the elastic bands didn’t hold enough pressure so there was a lot of flashing and the mould didn’t fill up as a result. To solve this we used pieces of wood and G clamps to to hold a greater pressure. We then poured for a third time with our smooth onyx resin.

Once it cured we opened the mould and it was perfect! We broke off the sprue and it was complete. The aluminium powder leaves a thin layer of metal on the outside which can be buffed but can be removed easily too. As it’s metal it gives a great metal finish and if you use an iron based metal powder you can even rust the surface.

As this mould is reusable you can pour over and over and over and they will all look exactly the same. This is useful for a small batch run.

Finishing 3D printed parts is a time consuming task but once you know the steps and have a good workflow it’s a really fun project to undertake. There are also other ways which use chemicals to smooth off 3D printed arts but maybe we’ll save that for another time!


Kirby Downey

Kirby Downey

Lead Designer at MyMiniFactory
I am a product designer from South Africa, currently based in London. I specialize in taking objects and adding a technical and mechanical side to it, first making it work mechanically before adding a story to the product using shapes and forms. This can be seen with the props from games I have modeled. I enjoy working with my hands, completing each project myself and with each product I take special care to ensure that every detail is perfect. I have a passion for 3D printing and the capabilities it has in today's world.
Kirby Downey
Kirby Downey

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