First off, I use the non-commercial CADsoft Eagle license, which limits me to a 3x4" board. I decided to use board mounting holes to do "double duty" - mounting holes and aligning the boards for milling. I pre-drilled a bunch of PCB 'raw stock' with two precisely placed mounting holes (more on that later).
Alignment pins need to be placed on the top side of the sacrificial board. To do this, mount the X-Y home block and home the X & Y axis. Then drill four 0.125" holes 0.3" deep into the top of the sacrificial board at:
- X = 3.80, Y = 0.15
- X = 0.15, Y = 0.15
- X = -0.15, Y = 0.15
- X = -3.80, Y = 0.15
|Sacrificial board, top view.|
(click for larger image)
PCB mounts to the left two pins (negative X coordinates) for bottom etching/drilling and flips over to the right two pins (positive X coordinates) for top etching/drilling. Thin double-sided tape is used to hold the PCB securely to the sacrificial board.