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I borrowed some XDA keycaps from a friend and cast moulds around them. Now that I have some polyurethane resin I should hopefully be able to try casting some caps tomorrow! Or maybe later in the week.

My first run of keycap casting was a partial success, partial failure. I forgot my pointy tool to get the air out of the keycap stems so there was a big bubble instead of a stem. Other than that they formed really nicely! Some very minimal bubbles on the outer edge of the top but the form and texture look great.

Second attempt at polyurethane casting was a success! The keys are fully formed and the outsides have no bubbles.

They even fit fine on my keyboard, although one is a little looser than the other. It's clear that this resin isn't black, just a dark grey.

The working time of about 7 minutes turns out to be accurate, which is about right for the 4 moulds I have. They seemed to need the full 1 hour cure time, at the minimum demould time of 30 minutes they were a bit too flexible.

Well that's a dead mould, and the last keycap didn't survive either :(

The silicone gets brittle over time. Depending on the mould, people say you can get anywhere between 10 and 120 casts from it (for something with features this small it'll be on the low end). It looks like this one only managed somewhere around 16 :(

Basically, casting an entire keyboard worth of caps is a bad idea. But I'm doing it anyway!

The full keyboard is getting there though! Some of the caps are a little loose so I had to put some tape underneath. It makes the fit of the stem a little tighter (hopefully without breaking the stem)

It's very tedious with only two moulds, and I'm out of silicone to make more. This is definitely making me want to get a resin 3D printer to make some custom shaped ones.

@gbrnt
Something I've been wanting to do. Did you rig up a pressure pot?

@Tay0 I haven't - when I tried polyester it was pretty clear, so we'll see how it goes with this one. Probably not great but there's only one way to find out! I have a makeshift vacuum chamber that can pull a *very* slight vacuum so I might attempt degassing.

@gbrnt
Can you pressurize your vacuum chamber from the other side of your vacuum pump?

@Tay0 Not really - the "vacuum chamber" is a glass jar with a check valve from a sous vide bag glued over a hole in the lid! I'm also just using the hand pump from the sous vide bags to pull the vacuum, which is why it's not much of a vacuum.

@gbrnt how did you align the legos with the key caps so the top and bottom molds line up?

@cinebox You can see in the first photo the keys are inside boxes, stuck down to a flat Lego piece with blu-tack (squishy putty stuff). I cast the bottom half of the mould first, then removed it and flipped it over (leaving the cap in place). That left the impression of the LEGO studs and the bottom of the keycap on the top surface, and I could then pour in more silicone to form the top half of the mould. If that's not clear enough I can find a video of the technique

@gbrnt for something cast in lego bricks, they definitely look professional!

@piggo Thanks! I think the vents could do with a bit of work to get rid of the bubbles. Or I could sort out a vacuum chamber or a pressure chamber, so there are less bubbles in the first place.

Generally I'm surprised this is turning out so well with minimal effort. Casting is pretty cool!

@gbrnt @piggo I casted Warhammer miniatures (I have a past as a miniature sculptor) in lego bricks in the past. It's one of the best methods. :D

@nuala hehehe my partner keeps trying to eat them too. Maybe I should get some brown resin and make a chocolate bar keyboard?

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