Keycap Profiles

Cherry

Keyboards of Cherry brand (Cherry is a German company).

OEM

Original Equipment Manufacturer. It means, a typical cheap keyboard.

SA

“Spherical Angled”, from Signature Plastics (a USA company that makes keycaps).

DSA

From Signature Plastics. (DSA stand for DIN standard height, Spherical Angled)

Basically, key profile are of 2 types:

• Uniform → all keycaps are shaped the same.
• Non-uniform → Each row has a different shaped keycap.

There are 3 shapes of keycap top surface:

• Flat
• Concave
  • spherical (surface of a sphere)
  • cylindrical (surface of a cylinder side)
• Convex. (usually for the spacebar key, or thumb keys Keyboardio Model 1)

Another issue, is how the key plate is shaped or arranged. There are 3 major cases:

• Flat. (like laptop, or non-ergonomic keyboards made by Microsoft, Logitech, Apple, and vast majority of keyboards.)
• Staircase. Each row is a flat strip, and rows arranged like staircase.
• Curved (Example: Kinesis Advantage2, Microsoft Sculpt Ergonomic Keyboard )

Critical, is how key top is angled to the key stem (axis of the switch). If not orthogonal, it means the angle of attack is not aligned with key movement, therefore inefficient.

• Orthogonal. 90 degrees to the plate. (Most common.)
• About 80 degrees to the plate. (typically non-uniform concave top keycaps.)

Another issue is how key stem is angled to the key plate.

Spherical and Cylindrical

Reference

• https://deskthority.net/wiki/Keyboard_profile
• https://deskthority.net/wiki/Signature_Plastics_DSA_family

Conclusion

I think the best key profile is uniform, flat, and concave top. Concave top helps your finger determine position of the key. Uniform is great for swapping keycaps.

Angled key tops are a hack, and non-uniform keycap profiles also a hack, and non-orthogonal stemp to plate angle also a hack. They are hacks to avoid having a curved key plate. They have this goal: for any key row, finger should hit the key top in a orthogonal way, and the direction of force should be parallel to the key stem, but not having a curved key plate. We should use a curved plate if one really want a ergonomic fit.