Hi....
I built my own CNC specifically to mill my own prototype boards.
I use an arduino with GRBL.
1) Export your PCB as a PRODUCTION GERBER
This generates everything you need,
2) Download FlatCAM ( only windows) it is free and wonderful.
3) Open the GERBER file for COPPER BOTTOM
4) Follow the rest of the FlatCam steps.
a) I use a .1 mm 10% CNC bit; works like a charm.
b) You must auto level your board. Don't skimp on this ste p. Get as many data points as you can get within reason.
IF you are doing .1 mm on center type of works you need more data points than doing 2 mm spacing work.
c) DO NOT USE THE CNC BIT FOR AUTO LEVELING. Use a hard steel or brass rod with a dull point.
I will be putting a video as soon as I get a chance. Happy Milling....