The reason for my CNC mill conversion was to enable me to make my own home PCBs. I’d done a few tests but had yet to actually make one that I was going to use. I thought I’d start with something simple and upgrading the ugly stripboard I’d used for the PeeLight seemed an obvious choice – it’s small and only used a few through hole components.
Learning to use Eagle for PCB design took a little while. It’s not awful, but not the most intuitive piece of software either. I stuck with it because it seems a good choice if I later decide to send the design of to a fabrication house and have it done professionally.
PCB-gcode is an add-in for Eagle and also takes a while to get the best from. I found there was lots of trial and error regarding settings before I got the sort of result I wanted. There’s a trade off with the diameter of the mill to allow you to do some fine work. Too large a bit and the software knows it won’t fit between two tracks so it doesn’t try and the pads aren’t isolated at all. Too small and you may find that it tries loads of passes where you do want a bit more isolation. I also tried lying about the size of bit – especially when some pads had a 0.08mm gap between them and I only had a 1mm endmill.
Here’s the finished PCB. One thing I really like is how I can also cut out the board (including rounded corners), drill the component holes, drill any mounting holes and even engrave text with perfect alignment as it’s all done on the same machine without removing the workpiece. See if you can spot one mistake where I stopped the milling and tried to move the work without raising the tool.
Most people use a V-shaped engraving bit for PCB routing, but I had varied results this way. I’m fairly sure my problems were down to the way I was holding down the PCB. I clamped it at the edges using the clamps supplied with the mill. The problems were two fold. The fact that my PCB wasn’t completely flat caused varying cut widths. Any gaps under the PCB where the clamps had made it bow upwards meant that the rotation of the knife-shaped 2 flute cutter caused vibration and gave ragged edges in places. I did have some excellent results, especially on smaller pieces, but not consistently. Then I tried using a 0.5mm endmill and got a much better result. Any slight variation in cut depth didn’t cause variation in width. The vibration also seemed to go, or at least didn’t matter. I will try the engraving bits again, but this seems to suit me for now.