I've just uploaded my Instructable on how I implemented a pcb drill using a USB microscope. It uses an inverted configuration as per Harvey White (attribution given in the Instructable). <http://www.instructables.com/id/USB-Microscope-Guided-PCB-Drill/> Mark Lerman
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[Homebrew_PCBs] PCB Drill Instructable
2014-09-18 by Mark Lerman