The PCB for this project was designed in Kicad with drill sizes and trace widths optimized for a 1/32" flat end mill. The board you see in the photos was created with an Othermill, ancestor of the Bantam Tools PCB Milling Machine.
Click the button below to download the Kicad source project with schematic, board, & library files
Since the PCB will play a major role in this keyboard's aesthetic, you may want to dress it up a bit. You could use paint to cover the top side in a custom color, but it's far easier to use adhesive vinyl.
I used Oracal 631 adhesive vinyl, which is repositionable and somewhat forgiving during application – similar to drawer liner or contact paper. Consider using Oracal 651 type if you want something more durable & permanent. Whichever type you choose, the following process should apply:
Cut a piece of vinyl significantly larger than the PCB – ~13cm x 8cm
Remove the adhesive backing and apply vinyl to topside of PCB
Turn the covered PCB over and use a sharp knife along the board edges to remove excess vinyl
Slice holes through the vinyl for each component lead & use cross-cuts for the larger openings (switch posts, standoffs, etc)