To begin, you'll need a volunteer key cap, masking tape, a razor blade, and some carving wax or some other carving medium (you could probably use some Crayons if you wanted). For my key cap, I used one from the WASD sample kit.
Set the cap on the masking tape. Try to make it as flat as possible. Then cut the tape flush with the key cap.
If you did it correctly, the base should look like this.
Next, you need to melt the wax. Use some sort of double boiler method to melt it. I did mine by using a canning jar in a sauce pan. Medium to medium high heat should do it. You may need to use something to stir it to make sure it's properly melted and I recommend breaking the wax into smaller chunks.
This was my first go at a wax mold. It's a wooden shim lined with saran wrap and taped together. Just carefully place the key cap in face down.
Later I used a cardboard mold lined with saran wrap that was a little easier and seemed to work better.
When the wax is melted, slowly pour it over the key cap. Following that, let the wax sit for a little bit to cool down, but make sure not to wait too long.
Open up your mold and let it loose. If you did it correctly, the wax should look something like this.
Next, you'll need to trim the wax to your carving size. I highly recommend doing this while the wax is still warm and easily pliable. You'll want to trim and even the base and get as close to the side wall as you can. Don't get too close while the wax is still warm though. If you do, you'll run into issues with it pulling away from the key cap. To get the wax close enough to the side walls, you'll likely need to wait until it fully cools, but for the major trimming, it's best to do it while it's still warm. If you don't get close enough to the sides, your cap will be too wide for your keyboard, a problem I ran into with this first attempt.
Alternatively, you could try casting a mold of the key cap, then pouring melted wax into the mold and building a cap to mold from that, but it will be more difficult.
Here are the tools I used to then carve the key cap.
Here's the finished product. I'm not the most skilled artists, so I wanted to start with something a little easier to carve.
There are some problems with this cap that I didn't notice at first go. First, it's way too tall and looks silly. I had about 1/8" more room to carve down that I just didn't think about. Second, I didn't follow my advice and left the sides a little too thick. Third, I carved it sideways. I forgot to check which side was the front of the cap and carved it 90 degrees off. I corrected that last problem by rotating half the mold 90 degrees, but the other two weren't noticed until the mold was already made.
For the molding supplies, I bought some Alumilite stuff from Hobby Lobby. If you use their 40% off coupon they always have, it's not too expensive. The molding silicon I bought is really pliable and I think a stiffer mold material would be better for future experiments.
Next you need to find some sort of form to put your mold in. For mine, I used an old laundry detergent measuring cup. You'll also want to put something in the bottom to lock the two halves of the mold together in the proper orientation. For mine, I used some modeling clay.
Mix your silicon with the reacting agent and pour it onto your keycap. Wait overnight before pulling it out. Since your mold is a two part mold, know that the mold making process is at least a two day job.
To keep the two halves of the mold from bonding, you'll need some sort of mold release. I used petroleum jelly for mine. I just melted some in a spoon and applied it with a Q-tip.
I also cut the base off of the detergent cup so I could slide it over the first half of the mold instead of pushing it to the bottom.
Then just mix and pour the silicon like before and wait till the next day.
When you're done, you should get a mold like this.
For my first try at a key cap, I used some resin. You'll naturally have some resin that pours out the edges that you'll need to trim up. When you pour the resin, you'll need to wait 48 hours before attempting to demold the cap.
I'm not really happy with how it turned out. The top half turned out alright (the eyes are a little messed up)...but there are some issues once you flip it over.
As you can see, the stem didn't turn out quite right. It still fits just fine and actually holds it to the Cherry stem, but it has some wobble and play.
For a first try, it wasn't horrible, but there certainly needs to be more experimentation with materials used to make it right. I've made another key cap in yellow (more translucent though) and the stem turned out a lot better, but I'm still not happy with the material. The resin I used just won't cut it and it seems to be really inconsistent even when the measurements are identical.
To sum up my feeling about resin as a casting material:
In the future, I might try for lost-wax casting with a fine medium like plaster of paris and silica mixture so I can make a metal cap or see if I can find another fairly affordable medium to use that's better than resin, but not as costly as trying to make a homemade plastic injection mold (which would set me back at least $400). I've also been looking into making a thicker glass key cap, but, again, there's the issue of cost since the minimum I'd have to spend to be able to use a kiln is ~$100 and I'm currently looking for work. It's still fun experimentation though.
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