Shanghai YinChaoChang a W722 lathe processing of metal parts, workpiece surface machining quality external circular no obvious problem, and the machine's vibration is small. But in the processing of main parts - rubber managers stamped drum, workpiece surface appear periodically outside round the chatter marks, general examination of hard to find the failure causes of machine tools. We adopt mechanical fault diagnosis technology to find fault location and fault machine of the machine, first nature of transmission chain of analysis and calculation, obtains each train parts, use characteristic frequency JGZY - 1C type mechanical failure diagnosis in the daily use of the lathe spindle 560 turn/points and 735 turn/cent two kinds of rotating speed sensor separately carried on the test, pick up the spindle box, respectively go knife box and slip board box to collect the vibration signal of signal filtered (stationary fault) and demodulation spectral analysis, got a lot of lathe vibration signal spectrum diagram. And the calculated value and vibration signal spectrum diagram compares analysis, find out the fault location and machine determine the fault properties. Replace the corresponding gear and bearing, fault phenomena disappear.