Mystic Seers

Plastic Resin Casting

Plastic Resin Casting - Part 1

I've decided to put together a basic "how-to" guide that covers silicone rubber mold making and resin plastic casting. I learned quite a bit over the last several years while building my B9 Robot, Flux Capacitor and several dozen Twilight Zone Mystic Seers'. This is will not cover plastic injection molding but rather the type of molding you can do at home. Hopefully you will pick up a few tips here that will help you avoid some of the pitfalls I saw. If you haven't already, you should first check out my Silicone Rubber Mold Making - How-to Guide.

I've link to most of the necessary supplies where available at Amazon.


When molding plastic resin parts, I've uses Smooth-On "Smooth Cast 300" series (300, 305, 322 & 326) with great success. You measure it out by volume so it is pretty easy to use. It's also pretty forgiving if your ratio is off a little. I have also used a 2 part resin called Por-A Kast "Mark-2".


If you want your resin part to have a specific color you will have to experiment with some coloring. I use So-Strong colorants. There are very strong and very reliable once you figure out how much to use. To get the desired pink-flesh tone I have to mix a drop of orange with a drop of red. That is enough to tint about 4 ounces of resin. I mix up a small batch of the Part A of the resin and keep it in an air tight container.


If you want to extend the life of your molds you'll want to have to spray on mold release. Lightly spray both halves of your mold and let it dry a few minutes.


Read more: Plastic Resin Casting - Part 1

Plastic Resin Casting - Part 2

I've decided to put together a basic "how-to" guide that covers rubber mold making and resin plastic casting and molding. I learned quite a bit over the last 5 years while building my B9 Robot and a couple dozen Mystic Seers'. This is will not cover plastic injection molding but rather the type of molding you can do at home. Hopefully you will pick up a few tips here that will help you avoid some of the pitfalls. If you haven't already, you should first check out my Silicone Rubber Mold Making - How-to Guide.


Allow the resin to set the required time. With the resin I use, sets in about 10 minutes, but I wait 20-30 minutes before I take the part out of the mold.


Here's the mold filled with resin. I use a rubber band to hold the mold together. You don't want the rubber band too tight or it will distort the mold. The registration "holes" you created when you made the mold should help hold the mold together. Unlike custom injection molding, this mold is not under any pressure from the resin. This is also a good time to tap the mold a few times to get any bubbles to raise to the surface. If you have any undercuts in your mold you may have to tip it back and forth a few times as well. You will learn real fast where your mold can trap air. For a few of my molds I pour with the mold setting at an angle. Then I set it upright. This prevents the air from being trapped while pouring.


Allow the resin to set the required time. With the resin I use, sets in about 10 minutes, but I wait 20-30 minutes before I take the part out of the mold.


Read more: Plastic Resin Casting - Part 2