Making Printed Circuit Boards with the Fab Lab

Marc Boon, Feb 2008

Step 2: Creating a toolpath for milling and drilling

Now we have our PCB layout, we can prepare it for milling and drilling with the Fab Lab milling machine. In this step we will create the toolpath for milling the outlines of the copper traces, isolating them from the copper plane of the board.

To improve stability of the circuit, we will not isolate the GND signal from the copper plane, but leave it connected to the plane. The resulting GND plane will greatly reduce interference and improve stability of the circuit. It also minimises the amount of milling required, thus reducing manufacturing time and wear of the milling tool.

In order to create the outline of the signal traces, and leaving the GND signal connected to the copper plane, I wrote a Eagle User Language Program (ULP) which will create the toolpath for millling the outlines of the traces and drilling the holes. This program is a combination and adaptation of several programs by other Eagle users found on the Eagle website (the original contributions are mentioned in my code).

To run the program, use the File | Run.. command and open fablab-mill-n-drill.ulp. You should see a dialog like this:fablab-mill-n-drill

Specify the tooldiameter (1.0 mm is recommended) of the milling tool mounted in de milling machine. It is not recommended to use a tool with a diameter of less than 0.8 mm.

Next, specify the signal which should not be isolated from the copper plane. By default, this is the GND signal. If you want all signals to be isolated, make sure this field is empty.

Finally, there is a checkbox which should be checked if you want holes which are larger than the tool diameter to be milled to their specified size. If you don't check this, all holes will only be drilled, and will have the diameter of the tool. In our case, this checkbox should be checked.

Hitting the OK button will create the toolpath for milling in layer 46, and the toolpath for drilling in layer 45. The result will look like this:MicroTV board

Note the contours of the traces written to layer 46, and the absence of a contour around the GND signal, which means that all holes on this signal are drilled in the copper plane surrounding the other signals. Larger holes, such as the 4 mounting holes of the video socket, will be milled to their final size after being drilled to the tool diameter, which can be seen from the milling contour written to layer 45.

Save the board, and continue with Step 3: Creating files for driving the Roland Modela milling machine.

Back to start.