Making printed circuit Boards

 The first problem I ran into was that Express PCB does not export the circuit board traces, only the component pads where the parts are soldered. The software company that gives away Express PCB for free, makes PC boards and they want you to send them the design so they can make the board. I had to open the exported DXF in my CAD software and add the circuit board traces.

 The next problem I ran into was that after a test cut, I found that the copper traces were only about .001" wide, which is way too thin. The problem is that in the CAM software, you have to profile around the outside edge of the traces. This removes the copper around the outside edge and leaves an island of copper for the trace. If you profile all the way around the outside of a single line, there's nothing left. I had to draw my copper traces as double wide lines, about 2mm wide. Now there was a nice sized copper trace left in the center after the cut.

 The next problem was the cut width of the tool bit. The smallest end mill I have is 1/32" wide, but it is a ball nose bit, so you can get a thinner cut if you choose the cut depth just right. In the center of this board, there is going to be a surface mount IC chip with a SOIC footprint. The mounting pads for that chip are very small. A 1/32" bit will not even fit between the legs of the chip. The pads for that chip are only .02" wide with a center to center distance of .05". This means that you cannot cut out copper pads for mounting the chip unless your cut width is less than .03". A 1/32" bit is .03125, so I would be removing a bit more copper from the IC chip mounting pads than needed, but .00125"  is not too bad. I see that most people cutting PC boards use very small diameter tools. Something like .005 to .01" wide. These tools are very expensive where as my 1/32" bit was about $7.

 The last problem was figuring out the tool bit cut depth. You want to cut through the copper on the board and that is all. I ended up choosing a .005" cut depth for the particular board I had on hand. The thickness may be different for other boards.

Note that if the PC board parts are not miniscule, like the SOIC chip I mentioned above, you can design the board with plenty of room between all the traces and a larger cutting bit would not be an issue. Surface mount components are very tiny and it is way harder to design a board for them. There's probably a way easier way to do all of this, but I don't do many circuit boards and so I don't really want to purchase special software for making PC baords with a CNC.