The comparison of keytop sizes of common profiles

In the previous post I told the importance of the keytop depth size. So let's compare the keytop depth sizes of common profiles. I made 3D models of them for P2PPCB. The figure and numbers below are the projection to the switch mounting plane.

• XDA: 13.7 mm
• DSA: 12.7 mm
• OEM R3: 14.3 mm
• Cherry R3: 15.0 mm
• Model M (not very precise because no 3D model just a caliper): 14 mm

As the theory which is described in the previous post, uniform profiles should have short keytop depth because they (usually) lack the step. XDA and DSA follows the theory. 

Larger keytop size is better to make legends readable. But smaller is better for reducing finger interference (it occurs between left and right keys too). From this viewpoint, I think Cherry profile does the best. It has long depth but the step makes it harmless. Short width is good for reducing finger interference between left and right keys.

I want you to pay attention to Model M. It has smallest (depth and width both) keytop among the stepped profiles. In 1980 IBM was a giant of the industry and invested much to keyboard ergonomics. The glory of Selectric typewriter was not long ago. To be honest, I think that the decline of IBM begun with Model F, especially Olympic-podium style wide keys. However it came from cost pressure, and the knowledge of R&D was not marginal. The keytop size of Model M might be best for professional typists (in 1980 they are still primary customers). Professional typists never look at keytops, so readablity is irrelevant for them.

So my Junana profile? Shorter than Model M, 13.1 mm. The requirements of 17 mm pitch and dye sublimation (five sides at once) was strict...