After getting the motor back, I then moved on to test cuts on the copper PCB substrate. The biggest challenge I found was holding the plate flat. In fact it seems impossible. The best I could do was fly-cut a piece of MDF, glue a piece of plexiglass to that, then glue the PCB board to that and clamp it real well with another piece of wood over it. This resulted in a variation of about 5 milles high to low.
Since the copper is probably 1 mille or thinner, 5 milles variation seems like a lot to me. So I set out to write a displacement map feature into the host software. I would manually sweep the PCB with my dial-test indicator and record the height on a 1/4" grid. I'd feed this into a routine that would adjust every point in the tool path that was at the cutting depth. I attempted to leverage the toxiclibs library that I've made heavy use of for the geometry of tool path manipulation. The documentation for the classes I needed was weak and I ultimately couldn't figure out how to get it done. I wasn't about to write the displacement geometry stuff myself, so I bailed and decided to cut some copper.
I mentioned somewhere in this blog that if I can put something together backwards or cut the wrong end off something I'll do it. My first attempt failed as I forgot to mirror the design to put the copper on the bottom of the board. My second attempt started out real well but failed when the drill bit wandered severely. I opted not to peck first with a center drill. My third attempt failed when my $20 15 mille end mill broke.
I will come back to PCB milling someday but only after finishing the displacement map feature (preferably with a probe). This will allow me to have little concern about holding the PCB flat and I can use cheap Dremel engraving bits.
At this point I plan to use the Fritzing Fab service to produce a professional PCB. I'd like to make my own for prototyping and experimentation, but it will be nice to have a high-quality board for the milling system itself. So now I'm redesigning the Sanguino I/O and Opto-isolation circuits on to one board and trying to shrink it as much as possible to save money.
