PCB middle pieces for the MLP keyboardThese PCBs are the same outer dimensions as the keyboard PCBs. Holes for each of the switches and the Pro Micro were cut out. This is probably more elaborate than needed. I could have just cut out larger rectangles between each screw hole. It is very sturdy when assembled.
I chose 1.0mm PCB so that I could match it with the correct spacer lengths which are all multiples of 1mm. I used 4mm M2 spacers which fit snugly in the middle pieces. Some were too tight and I had to sand them down slightly to fit.
Files are on Github.
No gaps for things to get into the keyboard. The main problem I have with sandwich style keyboard cases is the gap where things can make contact with the electrical contacts inside. You can see this gap in this post.
1.2mm top and bottom PCB and 1mm middle pieces.
Close up of the layers.