The actual process nobody bothers to explain clearly
Most people who want custom keycaps start with resin casting and hit a wall within an hour. The material choices, the degassing, the timing, the parting line problems - it is a lot to sort through without someone having actually burned their fingers on a hot plate. I ended up doing this for maybe two years straight, making keycaps for local builders and a handful of small orders. Eventually I learned which steps actually matter and which are just noise. The method comes down to a silicone mold made from an existing keycap you like, then casting your material into it. You can use epoxy resin, polyurethane resin, or sometimes even plaster for really rough practice pieces. Epoxy is the standard because it gives you a hard finish and reasonable clarity. Polyurethane cures faster but yellows quicker. If you are just starting out, stick to epoxy and buy the cheap clear casting kind from Amazon or a hardware store. Do not bother with anything labeled "jewelry grade" unless you have money to waste. Here is what you actually do. First you pick a keycap to use as your master. It has to be something you own already and genuinely like the shape of. A Cherry profile or a KBD75 OEM height keycap works fine. Clean it thoroughly with isopropyl alcohol so there is no oil or residue. Then you mix up a small batch of silicone, usually room temperature vulcanizing silicone, and pour it around the keycap to make a two-part mold. You want the silicone to be about half an inch thick around the entire cap so it holds its shape when you demold.
Once the silicone sets, which takes roughly two to four hours depending on your brand and room temperature, you carefully peel the two halves apart. The master keycap sits inside one half, and you remove it gently. Now you are ready to cast. Mix your epoxy according to the instructions. This is where most people mess up. They pour too fast and trap air bubbles. You need to either use a vacuum chamber to degas the epoxy before pouring or simply pour in multiple thin layers and let each one sit for thirty seconds before adding the next. If you skip this step your keycaps will look cloudy and weak. After the epoxy cures fully, you pop the raw keycap out of the silicone mold and trim any excess flashing with an X-Acto knife or fine sandpaper. The stem area needs careful attention because the keycap must still fit on a standard MX-style switch. I usually sand the bottom of the stem until it slides onto a switch without excessive wobble. A loose fit means your keycap will rattle or fall off during typing. A tight fit means you might crack the switch stem when pressing down. One practical problem I ran into repeatedly: the silicone mold would sometimes create a thin seam line around the middle of the keycap where the two mold halves meet. This seam shows up as a visible ridge on the finished product and feels rough under your fingers. My workaround was simple enough that I wonder why nobody mentions it. Before pouring the second half of silicone, I brushed a thin layer of release agent or even a light dusting of talcum powder onto the first half. This prevents the second silicone layer from bonding to the first at the seam line, making demolding cleaner and reducing that ridge. It cuts down on post-processing time significantly.
What the forums leave out about materials and finish
Epoxy resin is not the only option and honestly it is not always the best one for daily use. The hardness of cured epoxy sits around 80 to 90 on the Shore D scale, which means it feels hard and somewhat slippery. Your fingers will slide off the sides more than they do on ABS plastic keycaps. If you type a lot and want a softer, grippier feel, you should look at polyurethane resin instead. It cures to about 70 Shore D and has a slightly softer, more rubbery texture that many people prefer for touch typing. Another thing nobody warns you about is thermal expansion. If you cast resin keycaps and leave them on a keyboard near a warm workspace or in a hot car, the resin expands at a different rate than the plastic stem of a standard MX switch. I once had a batch of keycaps that became impossible to mount after sitting on a desk next to a space heater for a week. The stems were slightly undersized from the casting and the heat made them contract unevenly. The fix was just to lightly sand the inside of each stem until it cleared the switch stem again. Always test fit one keycap before committing to a full batch. Sanding and finishing is where you can either salvage a batch or throw it away. Start with 400 grit sandpaper to remove the biggest flaws, then move up to 800, then 1500, then 3000 if you want a glossy finish. Each grit removes the scratches from the previous one. If you rush this step, you will see the cloudy swirls under any clear coat or even in direct light. Polishing compound on a Dremel with a felt wheel works fast but it melts the resin if you hold it in one spot too long. I learned this the hard way on my first hundred keycaps. A whole batch looked frosted and ruined until I realized I had just been going too slow with the polisher.
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For dyeing or coloring, you can add alcohol inks or mica powders to the epoxy before mixing. Alcohol inks give you transparent colors that look great if the cap is backlit. Mica powders give you opaque metallic or pearlescent finishes but they settle to the bottom of the cup if you do not stir them in fast enough. The other option is UV resin, which cures under a UV lamp in minutes rather than hours. It is faster but more expensive per batch and it is brittle compared to epoxy. I used UV resin for a small run of accent keys once and three of them cracked at the stem after two weeks of normal use. Epoxy held up fine.
Real limitations you need to know before starting
DIY keycap casting is not a replacement for injection molding and it never will be. The tolerances are worse, the consistency between batches is unpredictable, and the time cost per keycap is high. A single keycap from start to finish takes roughly forty-five minutes to an hour if you are skilled, closer to two hours if you are doing it for the first time. That includes mold making, curing, demolding, trimming, sanding, and finishing. You cannot cast a full set of 104 keys in one evening unless you have pre-made silicone molds for every profile. The biggest bottleneck is the curing time. Even fast-curing epoxy takes six to eight hours for a full cure. If you try to rush it by using heat lamps or hair dryers, the outside cures while the inside stays tacky. This creates a soft layer that feels fine until you type on it for a week and the surface starts wearing through. Patience is the only real shortcut here. Let it cure at room temperature and do not touch it. If you want something closer to factory quality, buying blank keycaps from a supplier like GMK, ePBT, or even budget ABS blanks from AliExpress and modifying them is often faster and more consistent. You can sand them down, drill new stem shapes, paint them, or use vinyl wraps. Some people even use a Dremel with a small grinding bit to reshape the profile of a blank keycap entirely. This approach skips the mold-making step and gives you repeatable results, though you lose the ability to make truly unique shapes that no one else has.
Another edge case is stem geometry. Standard MX stems are cross-shaped and about 14mm tall. If you are casting for a different switch type, like low-profile switches or Alps stabilizers, you need to account for that in your master keycap. Casting into a silicone mold made from a Cherry MX master will produce keycaps that only fit Cherry-compatible switches. There is no way around this unless you make a separate mold for each switch type. I ended up with a drawer full of perfectly good resin keycaps that all had the wrong stem size for my actual keyboard. It cost me a weekend of re-cutting masters and remaking molds. Ventilation matters more than people admit. Mixing epoxy releases fumes that are not pleasant and not great for your lungs. Work in a well-ventilated area or wear a respirator with organic vapor cartridges. I used to do this at my kitchen table with the window cracked open and eventually got headaches that I did not connect to the epoxy until I read the SDS sheet. It took me two days to recover. Open a window and run a fan. That is all it takes.
