IBM Model F Foam Mat Purpose and Possible Alternative?

[THATGUY69]

I have recently purchased an Ibm model F At and have decided to take it apart and do a good cleaning. The foam mat is pretty much disintegrated at this point. I'm just curious what the purpose of the foam mat is? I heard somewhere that the purpose of the mat is to reduce electrical interference since it's capacitive. Is it possible to spray some sort of insulting spray, (Plasti Dip maybe) on the underside of the barrel plate instead of replacing the foam?

[fohat]

I have always felt that the foam mat served several purposes, but primarily a "bedding" layer for the barrels to seat into. That stabilizes and dampens them, and adds compression to the "sandwich" of plates that make up the internal assembly. I believe that it is this unresolved pressure that makes the Model F so "alive".

In my F-122 guide I go into detail on the matter. "Art foam" available at Michael's for $1 works great and is supposedly acid-free for long term stability.

workshop-f7/ibm-model-f-122-key-termina ... rry%20ansi

[kekstee]

I did print out the plate layout and got some cheap hole punching tools to recreate the foam mat.
Why risk half assed replacements for an assembly like that.

[Sigmoid]

I have recently purchased an Ibm model F At and have decided to take it apart and do a good cleaning. The foam mat is pretty much disintegrated at this point. I'm just curious what the purpose of the foam mat is? I heard somewhere that the purpose of the mat is to reduce electrical interference since it's capacitive. Is it possible to spray some sort of insulting spray, (Plasti Dip maybe) on the underside of the barrel plate instead of replacing the foam?

No idea where you have heard that, it's pure nonsense. The barrels themselves are not conductive, the capacitive sensing circuitry needs three things to function: the pads on the PCB, a conductive actuator (the flippers, or even your finger on a disassembled PCB - indeed, you can type on a disassembled Model F as if it were a capacitive touchscreen), and correct grounding of the metal backplate. The foam plays no role.

The foam mat primarily serves a mechanical purpose in these keyboards - it holds the barrels down securely on the PCB, and silences the keyboard a little (though "silencing" is pretty relative on a Model F).

The best route in replacing it is using an inert, good elastic foam mat as a replacement that you cut out with leatherworking punch tools.

[just_add_coffee]

This place is like Model F refurbishment central these days!

Regarding the mat, there are some different ideas around here ...
fohat's
Sigmoid's
tigpha's

And regarding cleaning, if you've got rusty springs, try some white vinegar.