Mold making: Lunax7070 Space Marine

A completed mold and the mold release that ensured each half of the silicone molds separated when pouring the mold.

Earlier this month, I started converting the components of one of Lunax7070’s True-scale Space Marines. After adding ball-bearings to some of the components to help with posing, I decided the model would be a good candidate for creating a two part silicone mold. Years back, when I first attempted resin casting, I created a series of posts describing the process, from the initial attempt to some tips to make the process easier. It had been quite a while since I made any molds or did any casting, resulting in this attempt not going as smoothly as possible. In the end, however, I was able to create a mold that will serve my purposes!

The compressor and pressure chamber I use when casting.

I used Oomoo 30 for the silicone molds and Smooth-Cast 300 for the resin, both from Smooth-On.

Like before, I used Oomoo 30 silicone for the two part mold, and Smooth-Cast 300 for the liquid plastic/resin, both from Smooth-On. For casting, I prepared the first half of the mold by pressing the model pieces into hard modeling clay and surrounding it with Lego bricks, which will contain the liquid silicone when poured. I used pieces of a sprue to create the runner, where I would inject the resin when using the completed mold. After mixing the two-part Oomoo 30, I degassed it in a pressure pot for a minute or two, before pouring it and letting it cure under pressure (~50 psi), in the pressure pot I built using an air pressure paint tank. This worked nicely, allowing me to pull the clay from the model pieces after the silicone hardened, without the pieces separating from the silicone.

The first mold didn’t separate properly when pulling the two halves apart, ripping at places along the left side.

Before pouring the second half of the mold, I wanted to add some mold release to ensure the two silicone halves would easily come apart. Unfortunately, instead of buying a non-silicone release agent, I bought a can of Smooth-On Universal Mold Release, which is silicone-based. While this is good for helping resin detach from the silicone mold, it is not effective for preventing silicone from sticking together. This resulted in the second half of the mold sticking to the first, which caused parts of it to tear when separating the two halves of the silicone mold. Despite this, I was still able to use the mold to create a few casts of the modified Lunax7070 pieces.

The second attempt at the mold worked a lot better, with the two halves fully separating after curing, due to the use of the Mann Release Technologies Ease Release 200 spray.

One of the initial casts using the second mold. While it is not perfect, with a few bubbles where it didn’t fill completely, the pieces are very usable.

While the first mold was serviceable, I decided to create a second one, this time adding additional runners taken from an old Gundam model kit. I also replaced the Smooth-On Universal Mold Release with Mann Release Technologies Ease Release 200, which also works on silicone. This worked a lot better, allowing me to separate the two halves of the mold without tearing anything. The use of the Gundam runners also reduced the need to do as much cutting to create working channels. The second mold works quite well, casting most of the pieces without bubbles. A few pieces sometimes do not fill completely, so I will have to experiment with it a little more. Regardless, it is functional, creating usable resin copies of the original pieces. Now I just need to build a model from it!

- Adam Wier