I didn’t know anything about plastics or silicon molds before starting this project. Everything I learned on this project came from my man Jesse (a former co-worker and master craftsman). Jesse used to build overnight set props for Hollywood movies. His techniques are beyond amazing.
I’m going to list this project in steps, but it’s not meant to be an all inclusive “how-to”.
1. Build a prototype fader. I took an existing Rane fader cap, and covered the sides in epoxy. I spent a lot of time shaping and sanding the epoxy to get my ideal fader shape and size. Since the prototype used an existing Rane cap, I was able to have a few scratch practice sessions with it to make sure it was what I wanted.
2. Prepare the prototype for the mold. This part is a bit tough to explain. I wish I did, but I don’t have photos of this step.
Here’s the concept: In order to get the plastic to the center of the mold, you have to create a tunnel. The liquid plastic will later be injected into this tunnel. More specifically, you need an entrance tunnel for the plastic injection, and an exit tunnel for the plastic overflow.
To create this tunnel system, you have to use some clever tricks. We cut a large paper cup in half (cut horizontally, so it’s just a smaller cup). Next, we glued 2 short plastic rods (one about 2cm meters long, and the other about 1 cm long) to the bottom corners of the fader cap. By bottom, I mean the side of the cap that the fader stem enters. The fader stood on the plastic rods like 2 legs. It looked kind of like a little robot, where one leg was b bit shorter than the other.
The robots feet were glued into the bottom of the cup.
Since I don’t have photos, you will have to use your imagination. Right now the fader is standing on it’s two legs inside the cup. Here’s a little preview, so that you know why we’re doing all this… We’re going to pour the silicon in the cup (totally submerging the robot), and then later (after the silicon cures) flip the mold upside down. This will put the tunnels, which were created by the robots legs, at the top of the mold. This will let us use gravity to our advantage by injecting the plastic downwards into one robot leg until it overflows from the other robot leg.
3. Pour the mold. You can get all types of silicon mold materials from places like TAP Plastics. They are common and easy to use. Follow the curing instructions on whatever mold materials you end up getting.
You have to be very careful about making sure all of the bubbles are removed from the silicon. This starts by carefully mixing it, pouring it, and tapping the bubbles out before it sets. Bubbles will make a mess of your final product.
4. Remove the prototype from the mold. With a razor blade, carefully cut a single plane into the top side of the silicon mold and remove the fader prototype. The cut doesn’t have to be perfect.
This is what the mold looks like with the prototype removed (notice the ridge around the top of the cup created by the bottom of the paper cup):
You shouldn’t cut the mold all the way through, but here is what the mold looks like when it is split all the way open:
You can see the two tunnels for the plastic injection, and the many wavy cut marks at the top of the mold created when removing the prototype.
5. Mix and inject the Plastic. Plastic is categorized by it’s hardness, the percent of the mix, and the cure time. I used a 50/50 plastic, because it made the mixing process a lot easier for me. 50/50 means that you have two liquids, and you need to mix them so that you have the same amount of each in the final solution.
I used this plastic:
I went to Walgreens and got a few free syringes. They use this syringe to feed babies exact amount of baby medicine (by mouth).
The syringe looks like this:
I mixed a very small amount of plastic in a paper cup, sucked it up into the syringe, and injected it into one of the holes in the mold (the shortest tunnel). The plastic overflowed from the other tunnel, so I knew that the mold was full.
6. Finalize the fader. Once the plastic cures (I let it sit overnight, but it cured much faster than that), remove the plastic from the mold. Cut the legs off of the fader. Sand the fader with a light sand paper for texture.
The only issue I had finalizing the fader was the hole for the fader stem. After making a few fader caps, the small piece of silicon that created the hole for the fader stem broke off. I ended up having to carve the depth of the fader stem with a box cutter. It’s not difficult, but it took more time than I would have liked. Jesse told me when the project started that we should be using the real stem from the Rane fader in the silicon mold. He knew this would happen. I didn’t want to destroy my mixer, so I dealt with the consequences. Later, I ordered a fader stem from Shaun W. at Rane for about $15. I didn’t end up making more fader caps (because I really liked the version I made), so I never ended up using the fader stem in a new mold.
I really love this fader cap. It’s the only cap I use for cutting right now.