Had similar problems with (video) CMMs in the past. A nice indicator and a good excuse ;) is a cup of black coffee. The reflections of the room light at the black surface make a quite sensitive indicator to seismic problems.
We had a similiar seismic problem with our visual grinders at our plant in York, PA. It turns out there was a surprisingly well-kept secret that much of the city was tunneled-under by a limestone rock quarry 400 feet down. The local toolmakers all knew about it from the ruined work pieces whenever the blasting below shook the ground like a semi-trailer truck or train going-by at a critical finish grind, but there was no highway or train track close enough to explain it.
I always thought it was strange that such a major operation was virtually unknown by most of the general public.
It is always interesting to see how things that are assumed to not have any influence do have an influence. The CMM does wind up being a very sensitive device, and probably should contain an internal accelerometer to warn a user about machine vibration.
I can't tell you how many times the Sherlock Ohms cases involve some oddbird activities that affect a nearby process. Let us know your stories about weird performance oddities that took some investigation to solve. Send your Sherlock cases to Rob.spiegel@UBM.com.
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