Dec 27, 2023

The relationship of step, keytop depth, keytop height, and switch travel

Aside from XDA and DSA (uniform profiles), common keycaps are designed like the figure below (Cherry profile):

The green arrows indicate "step". This gives keyboards beautiful undulations. The origin of the step is probably non-electric typewriters like this:

The purpose of the step is to avoid finger interference while pressing:

Old non-electric typewriters have long step, and recent chiclet style keyboards have zero step. Non-electric typewriters have long travel so they require long step. Recent chiclet style keyboards are the opposite.

Keytop depth (near to far) also plays a role. You can avoid finger interference by reducing keytop size of depth direction. This is a big reason why chiclet style keyboards have gaps around each key.

Finger angle also plays a role. The step is useless if the finger is perpendicular to the switch. Therefore R4-R3 step should be larger than R3-R2. The Cherry profile figure above follows the theory. However R1-R1 step doesn't. In this case, another phenomenon is in play. See figure below:

This layout has zero R1-R1 step, and in my experience with many prototypes, this is a bad idea. I felt my fingers cramped in this layout. I felt much better below:

In near rows, the step doesn't play a role. Instead of the step, keytop angle plays a role. The keytop height should be flat in near rows. I have no idea about the theory behind the phenomenon.

BTW all the figures above are created by P2PPCB Composer F360. This is also good for making figures.

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