Introduction: Easy Silicone Mold Making for Epoxy Casting

By Narwhal Labs
About: Narwhal Labs is a community and makerspace that encourages and supports creative building, learning, and experimentation.

Phillip Danner of Danner Builds drops by the lab to show us his secrets for making silicone molds used for casting epoxy resin. Using only a handful of tools you can make your own molds for casting epoxy resin and more. Basic molds can even be made with a scroll saw or etching with a rotary tool. Sharing of knowledge is one of the things that makes the maker community so great - thank you to Phillip and Elizabeth Danner for coming to Narwhal Labs and teaching us their skills and techniques.

Follow along in this instructable and watch our video to learn some tips and tricks for making your own silicone molds!

Supplies

Step 1: Cut, Engrave and Clean Acrylic Mold Masters

Start by cutting out your masters. These acrylic masters were cut on our Thunder Laser Nova 35, but you can make your mold masters using a number of supplies and tools - use your imagination! We engraved on our 100W CO2 laser at 400mm/s and 15% power.

Clean the masters with a dry paper towel to remove the acrylic dust. Clean the remainder with some isopropyl alcohol on the face of the acrylic, but be careful not to get alcohol on the edges, it will cause crazing. Finish cleaning them with a microfiber cloth. Be sure not to touch the faces of them with bare hands after this step.

Step 2: Assemble Your Mold

Put on nitrile gloves. Remember that latex gloves even being near your mold or masters will inhibit the silicone curing and ruin your project.

Place a sheet of Oramask Vinyl Stencil Film sticky side up on a flat surface. Adhere your masters down to the film.

Put up walls 1/4" taller than your masters around the border. We used acrylic, but you can use cardboard, foamboard, or corroplast. Hot glue all the edges to prevent silicone leakage.

It's a good idea to cover your masters at this point to make sure no dust or contaminates work their way into your final product.

Step 3: (Double) Mix and Pour Your Silicone

If your silicone is unopened or has been sitting for more than a few days, use a drill mixer on slow speed or a spatula to mix up the individual silicone parts before dispensing it. Some solids will settle out and need to be reincorporated. Do not share mixers between part A and B or you may trigger a cure in the entire pot.

Calculate the amount of silicone you need for your pour. It's a good idea to mix extra - some will be left behind in the mixing pots.

Mix the mold star 15 in a 1:1 ratio slowly by hand, scraping the sides and bottom as you go.

Transfer the mixed silicone into a secondary container and mix again for another minute or two. Do NOT scrape silicone out of the first container. This will ensure we have no unmixed silicone. This is known as double mixing.

Pour the silicone from high up with a thin stream to the lowest/base point of your mold - this will minimize or eliminate the amount of bubbles in the final mold.

Let the silicone cure for the recommended time - this silicone has a 4 hour demolding time.

Step 4: Demold the Silicone

Demold by flipping the cured piece over, and peeling the oramask film off. Remove the sides of the mold.

Trim off flashing, if any with a cuticle trimmer for a nice clean look.

Carefully remove the masters just like you would demold epoxy, and save them if you'd like for a future project.

Step 5: Use Your New Mold for Epoxy Casting!

All done! You can now use your mold for casting epoxy and urethane resins. See TotalBoat's video above for an example of what to do with this mold from DannerBuilds.

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