I am still a little confused after reading your great guide. I have a Filco M2 Camo with black switches, what size o-ring would I need to minimize the travel as much as possible while still having a switch that works and caps that stay on? First timer with Mech keyboards, thanks in advance for any insight!
You have keycaps that are considered OEM (they are taller than Cherry). The switch has a travel distance of basically 4mm. I tend to like a minimal travel reduction while still giving good dampening. I personally like a travel distance of 3.5mm with o-rings. I achieved that with an o-ring that was 1.75mm thick.
You are looking for basically the minimum travel distance you can have with OEM caps. I have tested this only with Cherry keycaps. With Cherry, I use a 1.45mm o-ring (small from IMSTO) to achieve the 3.5mm travel distance that I like. When I used the 1.75mm o-rings with Cherry, I had a 3.15mm travel distance. The switch still operated, but it was VERY close to the key activation on my MX Browns. I don't think you can do less than 3.15mm and have a reliable key activation. Also, the key caps do not go all the way on when you have 3.15mm travel distance. I was not concerned with the caps coming off, but I definitely realized they were not on all the way. I would recommend you use the softest o-ring you can find if you are going to try to limit the key stroke distance as much as possible. This will allow you compress the o-ring a bit when you apply the keycap and the cap will go on farther. Also, I think the softer o-ring will be more comfortable with this setup.
So if I do some math here I would deduce you would need the following to limit the travel distance as much as possible with OEM while still having a functional switch.
Cherry:
3.5mm travel => 1.45mm ring | 3.15mm travel => 1.75mm ring
1.75mm - 1.45mm = .3mm | 3.5mm - 3.15mm = .35mm
The keycap now goes on .05mm less which accounts for the difference between .35 and .30
OEM:
3.55mm travel => 1.75mm ring | 3.15mm travel => X ring
1.75 + .3 = 2.05mm | 3.55mm - 3.15mm => .4mm
This is not an exact science here. There was probably about a .05 margin for error with the measurements.
I think I would recommend 2.05mm o-ring or there abouts to reduce the travel distance as much as possible. I am tempted to say 2.10 because of the numbers, but I personally found this to be really uncomfortable, so if you have not tried it, I would error on the side of a bit smaller than you think, so I will stick with 2.05 as my suggestion.
I have not seen o-rings of that size (personally, if you want to sent me a couple and you know there source I can do tests). The o-rings I have seen/tested are the ones in this picture. I can test the 1.95 with an OEM cap if you want...
Thats the best I got for you...