Originally Posted by
CaptainObvious
Hmmm, looking back at that I think there's a big issue, the GND in the power supply is not actually connected to Ground (Earth Ground), and I don't think it would be a good idea to connect them together. So in that circuit current would be flowing from the +5V to Earth Ground, I'm not very knowledgeable in grounding techniques (it probably shows!) but that seems like a no-no to me.
So the issue then is, if the spindle is grounded (Earth Ground), also the machine frame and the work piece also is grounded, how would a tool sensor work?