Membrane keypresses work when a conductive membrane bridges two contacts on the PCB. To make it work with mechanical switches, all you need to do in theory is replace the conductive membrane with the switch pins.
In practice, it’s quite tricky to hand-solder switch pins to a PCB surface contact that wasn’t specifically designed for soldering mechanical switches onto - or anything, for that matter. So I used some jumper wires to make it easier. (Fig. 1.)
I drilled holes in the plate to feed the jumper wires through. (Fig. 2.)
Some throwaway Kaihl blacks. Not my favorite, but better than membranes for sure. (Fig. 3.)
This was much harder than I initially thought it would be. I had to secure all the switches in place with hot glue too, because there’s nothing for them to latch onto here. (Fig. 4.) Because the spacing was really tight, I can’t use regular MX keycaps. So I repurposed the original numpad’s keycaps to fit instead. All I needed to do was dremel a cross into the cylindrical stem it originally used. Had to dremel off the sides though, as my alignment of the switches was far from perfect and the keycaps would keep bumping into each other. (Fig. 5.)
Now I can actually use the thing. (Fig. 6.)
I made this. (Fig. 7.)
Manny says “Hi.” (Fig. 8.)