This photo shows 3 versions of the Tiny Duino board I first described in July 2014. The board on the right is laid out in Fritzing and etched using the toner transfer method to create a mask. The other 2 boards were laid out using Eagle and produced on my little desktop CNC machine seen in my October 2017 post. The default components in Eagle are good for commercial production but created pads and lines that were too fine for this method.
The first step was to learn a little about Eagle CAD. Eagle is free for hobbyists making small single sided or double sided circuit boards. You can edit components by opening the library containing the component and then double-clicking the package file for the component. I made the pads bigger and the drill holes smaller. Later when the CNC machine does the drilling the hole size is determined by the physical drill you place in the machine. I used save-as and put "my" in front of the library name to make it easier to find later. You will need to open your new libraries using the Library manager in order to be able to use them. You can find some tutorials online to learn more about this. In Eagle 8.6 the component libraries are in /cache/lbr. I put the libraries I edited into Github. Library files contain large collections of components. I only edited the components used on the TinyDuino.
Since I had already laid out the TinyDuino board for etching I found it quicker to place the components on a new board in Eagle and then create the traces. This takes 2 steps. Firstly use Signal to join the components and then Route to create the trace. You can move the traces around and create bends. I made the traces 20 to 30 wide. Ground traces that are wide then the rest make it easy to identify ground later on. Make sure they are all on the Bottom since you are making a single-sided board.
The Make Your Own PCBs on an Inexpensive Desktop CNC machine Instructable article by davr.org helped me figure out how to use EagleCAD to generate the G code for my own desktop cnc mill. The pcb-gcode-EagleCAD plugin file contains a good manual in the docs folder to help you figure out the next steps. The plugin uses Processing and also generates a graphic so that you can double check your G Code. I used the single pass isolation mode and a 0.5mm end mill. Keep the spindle speed high, the feed rate low and run the code with the bit cutting air first to make sure the code works.
G code visualizer from the Eagle plugin.
Everything about this project required learning, trial and error and time. I was very pleased to see the final TinyDuino boards being cut. There were several trials until I got everything right. I think it really helped to do this with a circuit board that I am already very familiar with. I feel more confident that I can use this method to make a prototype circuit board in the future.