Sure, I'll spill: It occurred to me a couple days ago that small runs of perfectly serviceable keycaps might be made using vacuum forming. Sheet styrene and ABS come in various colors (including clear). I've never done it before, but a home rig is easy enough to make.
The trick will be making the mold. I initially thought I could just use a keystem mounted a little above the vacuum table, which should form the retaining tabs at the bottom. But I realized that the keystems don't have any concavity; that is built into the thickness of the plastic in the keycaps. So, that means that the mold will have to have the retaining tabs and the concavity while 'bottoming out' on the keystem. I may actually have to make a female mold, rather than a male, and suck the plastic into the keycap mold instead of over it.
Anyway, if I can find the time to get this done and it's a success, the idea is to run off sheets of keycaps and send them out to be cut and finished by the buyer.
I have already done the vacuuming of keycaps and it is a viable method. But depending on its use, perhaps very undesirable. It is however easy (very easy) to make a "home" vacuum box/frame. Using clear styrene, abs, acetate, acrylic, pvc...(you get the point) I have made a few nice little key caps that I have color coded (you can paint them on the inside or put commands in them) and they dont wear.
Don't vacuum into a mold, vacuum over a mold/buck. It's far less efficient sucking into a mold or blowing into on as opposed to slumping over one. The key stems in a model M have a very nice draft angle to them and the will easily produce the results you want. If you would like to be more productive with it you can either make a mold of the key innards (key stem) and duplicate it over a board, or just simply use spare key stems and drill them so that they are slightly rasied above the vacuuming table or board. If you raise them to much cleaing or de-flashing will be a pain in the ass. When you end up with a sheet that has a bunch of keycaps on it you can then either use scissors, x-acto or a paper guillotine to separate. If the plastic sucks under the keycap it will be a pain in the arse to cut out (relatively speaking of course)
You can do this with many different plastics and colors and even make certain textures if you are savy enough (captured vacuum forming). The real attention must however be paid to when you vacuum the plastic. Plastic undergoes three-four simple stages just before its ready to be slumped or vacuumed.
1)it buckles under the heat
2)slumps/sags under the heat
3)tightens back up (raises)
4)sags again (relaxes)
Stage 4 is when you take it away from the heat source and slump or vacuum.
Try to steer clear of heating while slumping, it can cause excess thining and/or deformation.
If you are wondering where this experience is coming from, I have been a professional mold maker for over ten years in the special effects industry.
Hope that helps and have fun.
(it is also a nice way to make a clear keyboard cover, that could fit as snug as a bug in a rug!)
