I use TiNi coated step bits for the switch, pot, and 510 holes. They arent necessary for the 510 hole or even the pot though. Regular TiNi bits for other holes such as the on-off-on external pushbutton, etc.
Then I use small 1/16" bits to drill around the square for the voltmeter, punch the center out to get the rough square and it's all files and patience there.
I used to try to use cutting wheels on a dremel to assist in the voltmeter cut but I found out real quick that doesnt work well for me. I get much better results with just the drill press and files.