My VMC currently has a drive belt on the spindle that is a bit damaged. It gets loud when running at high speeds. I'd think, since I can hear it, an accelerometer could sense it.

Vibrations can indicate most component mechanical faults including bearings, gears, belts (if present). It can be used for monitoring tool issues such as missing tool, loose tool, tool wear and tool breakage. Generally spindle balance and bearings are the primary focus. Saving maintenance costs may not be as important as maintaining product quality and production. If your company has CNC machines, then ask operators and maintenance personnel for their concerns and requirements. There are several vibration systems ranging from portable meters to online monitoring for machine condition and tool issues.

Walt