... fingers are not machines. ...
Yes, they are. Bone structures with tendon and ligament connections, muscle motors and built in sensors, very complex machines, but still machines.
... What is not shown is the re-action of the key to that force that is applied...
That is precisely what a force diagram IS showing. The upward reaction force on a pressure sensor during a keypress. The sensitivity of the sensor is lower than that of your fingers, though, so it doesn't tell the whole story.
As I said, a sensitive multidirectional sensor should show a spike in the graph when BS springs hit the case side. With blues it depends if the white part hits the slider (in which case it will be felt more strongly) or if it hits the bottom of the case (where the force would be absorbed more) due to the mass difference between a slider + keycap (which will change with keycap mass) and a full keyboard. If it is the former, thin, light keycaps will allow the force to felt more strongly, thick, heavy keycaps will dampen it a lot (which could explain why I don't really feel it since I like and use heavy caps).
So, shall we conclude that there are four components to tactile feedback from key switches (leaving out Alps since I don't know enough about their internal structure):
1. Change in pressure due to the action of (A) a bump and leaf or (B) a rubber dome collapsing or (C) a spring buckling (as can be seen on force diagrams)
2. Sharp, low strength force due to (A) small plastic part of the slider stopping suddenly or (B) buckling spring hitting the side of the switch casing.
3. Sharp change in pressure due to bottoming out the switch.
4. Sharp change in pressure due to the switch slider hitting the top of its travel (although this is usually subtlely felt).
Linear switches have only number 3 and 4. MX Browns, Clears and Topres have 1, 3 and 4. MX "clicky" switches and Buckling Springs have all 4.
In the case of the MX switches, the spring strength and bump size affects the relative strength of the leaf and bump interaction (compared to the spring pressure at that point), so heavier springs or smaller bumps result in a decrease of type 1 tactility. Softer springs or larger bumps result in an increase.
Different people seem to be more sensitive to different types of tactility and thus regard different switches as "more" or "less" tactile. ie: It's personal. I happen to be more sensitive to type 1, 3 and 4 and less to type 2.
There is a 5th factor affecting
perceived tactility. Aural feedback. Switches which "click" reinforce the type 2 tactile sensation by confirming what one sense is experiencing with feedback from another sense. Some have reported that adding a software click sound to a linear switch keyboard creates a sense of "tactility" or enhances the existing tactility of a keyboard with soft tactile switches and thus reduces typing errors and accidental actuations.
