Homebrew PCBs

>Has anyone tried attaching a very fine pen to a cnc then etch the pcb
>board? Right now I'm using pcb-gcode but it's a pain because it takes
>so long to remove all the material when 95% of the board is empty
>space and 5% traces.

(mechanically) etch only isolations, not entire  copper.
Google for "mechanical etching" to see what's about.
Cristian