I use a PCB CAD design package to create GERBER plot files of the PCB layout, and then convert this to G-Code using ‘DeskPCB’ from IMService (Google them..). It works quite well, some warts in the conversion that you can work around, but when you know how to do it, it works VERY well, I have milled many boards, with surface mount integrated circuits down to 0.6mm pin spacing. DeskPCB was around $100, if I remember correctly…well worth it. The secret is in having the PCB co-planar with the the engraving cutter horizontal path, and a very sharp cutter, 60 degree V tool, penetrating the copper about 0.02mm below the copper underside. High speed is essential, around 25000rpm min.
Joe