Two-part MX keycap idea

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21 Jan 2023, 18:07

I just had a random thought.. why not make MX keycap molds for two-part keycaps like IBM did for BS keyboards? I know the two part keycaps for Model M/F are generally considered inferior, but they didn’t serve much purpose there, whereas they could serve a very real purpose in the Cherry MX world:

Namely, you could create the row profile by varying the lower keycap heights and angles, while having identical shaped upper keycaps / ‘shells’.

Want profiled keycaps on a weird ortholinear Colemak thing you built? No problem, move the top caps around any way you like.

Want to swap the R4 Control and R2 CapsLock keycaps? No problem, just pop off the upper parts and maintain the row profile.

The keyset doesn’t even need to include duplicate keycaps to cover multiple rows. Keysets would be smaller and therefore cheaper, as with uniform profile keysets.

The same keyset can even be changed to a different profile entirely as new lower-cap molds become available.

Naturally, the initial investment in tooling would be substantial, and it might not support double shot legends; but the benefits down the line seem pretty great?

Has anything like this been attempted before?


21 Jan 2023, 23:45

Scarpia wrote:
21 Jan 2023, 18:07
Has anything like this been attempted before?
Sort of. Relegendable keycaps that are MX-compatible exist, made for cash-registers. Including full alphanumeric keyboards. The Tipro MID is especially low-profile.
But all of them are uniprofile. Most are flat. I don't think any of them are very nice to actually type on, and Cherry home-row profile is lower — with less wobble.

These cover only more or less of the top. Model M keycaps cover the entire key, and both parts have quite thin-walled "skirts".
Thick-walled MX keycaps are moulded to fit around a MX switch perfectly, whereas there is more space around Model M/F barrels.

Also, Model M and Model F have a curved backplane, with Cherry MX getting curvature from each keycap row being different. To be able to switch keys between rows, the tops would need to be thin, with the base containing the skirt, supported by some very thin struts from the key stem, or otherwise the bottom of the skirt would be wrong.

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22 Jan 2023, 13:38

IBM’s curved backplate makes all the difference. The modular simplicity you’ve spotted on Model M is actually due to that, not two piece caps. IBM’s single piece caps are just as row-agnostic. The curved backplate beneath them is the reason for that.

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24 Jan 2023, 22:36

Wow, did I really sound so clueless? I'll have to explain better:

First, I know about relegendables and I'm not talking about those, since they are generally a perfect storm of uniform profile, hideous and uncomfortable.

And yes, I'm aware of how BS backplates and buttons work; my proposal was to achieve a sculpted row profile with switches mounted on a flat PCB, same as any other sculpted keyset like SA or MT3, but using two-part keycaps to achieve interchangeable keycap 'shells' on top of varying-sculpted-row 'struts'. I was only using the two-part BS buttons as an example of how you could attach the upper and lower parts of the keycap.

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24 Jan 2023, 22:51

Fair enough. There are showstopping problems for this approach as well, though.

1. Obviously, all existing MX caps would be incompatible. ← I’d consider this a complete STOP to the idea, myself. But as you’ve inspired me to think…

2. As Fin alluded to: IBM caps have long skirts. That’s really important for the lower rows, which are tilted back compared to those above them. Tilting back exposes the front of the keys. They must be long to match.


The trouble then becomes what do you do with those caps when you want them on higher rows for different layouts? Home row in particular just won’t accept that. The caps must be long and yet also they can’t be long.

If the outer caps are short, you’re going to see a lot of bare switches with bungs in them exposed at the very front of your keyboard.

3. For as much as I like IBM keyboards, even the nicest Model F’s caps suck compared to most decent keyboards. I’d rather have Topre or MX caps on them if it weren’t one hell of a hack to make that happen. Buckling spring caps are thin and flat. I don’t like them. The typography makes up for it, and the keyfeel wins me over, but snap-on caps for other switches? Does not appeal, I must admit.

Beamspring caps and their tribute acts on MX: that’s where to be. :D

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25 Jan 2023, 19:50

Thanks Muirium! Those are really good points!

What if the interchangeable shell “skirt” only covered the top ~3-6 mm like a flat little hat? To reduce the eyesore you’d have to design the “strut” to include the rest of the skirt.

This would leave a visible division/gap where the top “hat” meets the strut “underskirt” (I’m enjoying this analogy too much) and that would of course mean you’d need to buy color matching struts with each new set of colored top hats.

I get that the seam between the top and bottom parts would be a hard pill to swallow visually (and the sound profile would most likely suffer, as would any hope of RGB support), but I wonder if the upsides (price, row freedom) might make it a compromise worth making - not for everyone but maybe for those with special layout needs?

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