Tool bit monitoring for on-vehicle brake lathe

A system and method for monitoring the contact of tool bits of a lathe with surfaces of a brake disk being machined employs a vibration sensor coupled to the lathe. Signals from the vibration sensor are processed as time-averaged segments that can be grouped within time intervals; a microprocessor employs a qualifying routine to compare the signal level to a background noise threshold value and indicates as "failed" those time periods where the average signal level is not above the background noise threshold. An accumulator records the indications over a number of intervals and compares the result to a standard to make a determination of whether the lathe is likely actively cutting the disk surfaces. To isolate intermittent, high-intensity noises, a consistency routine can check further to see whether individual segments within an interval fall within a range based on the average signal level for that interval.