I do not enjoy admitting defeat on anything. I find myself checking and rechecking my work until I realize an entire weekend worth of work was wasted by not admitting defeat. At this time, and after an entire weekend of work, I must admit that milling PCBs with a 1.0 Darwin is not possible. The reason for this is quite obvious, in retrospect. Put simply, the force required to etch copper is enough to twist the X axis guide rails. When the guide rails twist, while moving the toolhead in the -Y direction, the milling bit gets pushed into the milling surface. This results in a really bad situation. If the design requires further milling in this direction the bit eventually pushes clear through the 1.5 mm board and into the table.
Here is a picture of one of six goes I had this weekend.
As you can see, when milling just to scratch the surface the resolution was perfect. When attempting to mill through the copper the bit would catch and dig right through. I put a piece of red tape where the bit went through to make it stand out.
I still think it may be possible to pull PCB milling off if you are willing to redesign the x-carriage, but I am against drifting this far away from the original Darwin design. For anyone wanting to go as far as redesigning the x-carriage, I envision mounting the milling head between the guide rails. In this way, if the guide rails twist, the bit should retract from the milling surface in both the -Y and +Y directions. A better long term solution would be to use a design closer to a McWire for milling / subtractive manufacturing and the Darwin for additive.
At this point I have gone ahead and ordered a stepper motor driver board from Zack's new shop
. When I regain my motivation I will continue working on my extruder.