http://www.linuxcnc.org/index.php/english/forum/31-cad-cam/20632-routing-bitmap-contour
1. Make image as black face (B/W image) in Gimp or similar
2. Import to Inkscape
3. Trace bitmap
4. Delete bitmap – leave traced image
5. Zoom to border and set grid or guide to cutter radius
6. Do multiple Outset (need step small enougth) and observe vhere is enougth.
7. Use GcodeTools Inkscape extension – Path_to_Gcode
That’s all….
Step 6 is little tricky. I can’t set proper step to do it in one Outset operation. So I set that step to small value and observe result when is right amount. It’s easy if the grid is set to the cutter radius and image aligned to grid. Just apply Outset to reach next grid line.
I got good result with that.
Here is a FRITZING to GCODE solution
http://www.instructables.com/id/PCB-designing-and-isolationmilling-only-using-free/?ALLSTEPS