I think there's barely enough room. A key is 19mm wide. I guess the top width is a little too skinny. Perhaps wider tops than usual?
Ok, I don't seem to be getting through here. It is not even close to working with 6mm
Pictures might better illustrate it. This model has been split in half for illustrative purposes:
Show Image
Show Image
The above cap is about 1mm thick. Now imagine a cap which is 6 times as thick on all sides, and which can't expand outwards either since the distance from switch to switch is 19.05mm. Even if the stem is made of something else, a 6mm thick cap will leave you with 6mm from one side to the other on the inside of the cap. That isn't even enough for the stem, let alone the entire switch.
Edit: Hopefully that will clarify things. Their requirement of 6mm minimum wall thickness just renders it impossible to make a reasonable key cap in ceramic with their machine.
What a great picture of a switch! It can't be easy to cut that thing in half.
Wait a second: that's an amazing render! Excellent!
---
About wall thickness: Cherry MX is certainly out, but I don't think that it was ever a good choice for keycap / materials experimentation. The stem has to be quite narrow to fit in the cap, and you have issues with the switch clearance. Maximum wall thickness for standard key spacing is like 2mm, not counting the stem.
Key switches that are a bit taller like M7 or hall effect don't have these issues. Awhile ago, I proclaimed hall effect to be the easiest switch I know of to make keycaps for. I think even the 6mm requirement doesn't prevent it from use (in spacebars), though I will have to measure to be sure.
I like to imagine 6mm as the size of a "large" headphone plug. It's a common item that's defined to be that size. Most people in the USA refer to it as a 1/4" TRS plug. Hopefully this'll help other people here as well.
