I have milled a few PCB's. I generally lay out the circuit using Protel, but any PCB software will work. Then I save a copy as a DXF drawing and use AutoCAD to draw lines around areas that are all connected together (think of an island with all pads connected by traces). Any pads without traces on the layer (e.g. bottom but not top layer) get a rectangle around them. Then I use my CNC software (BobCad) to create an NC file that I can machine with my machine (Bridgeport mill converted to CNC). I made spade bits out of broken carbide (1/8" diameter) drill shanks to use for cutting. Simply grind a point on the carbide, then grind a flat on one side exactly half way through. It will cut the copper, leaving a slight burr, but easy to sand off after milling. This technique leaves gaps about 10-15 mils wide (depends on depth of cut) between islands. If you are using surface mount components, it is easy to place them bridging a gap where needed. The attached files show details about this.
Bob
