Abstract: The predictive apparatus and method for preventive maintenance of rotating CNC machinery for application to a multi motor machine tooling operating under computer numerical control with provisions for a program control using the computer (22) and a multiplexing device (24) with steps for measuring the constant load momentum of inertia while running each motor and load alone from start to f speed and to the inertia idled stop while recording the performance factors and calculating a plurality of relationships with steps for setting the allowed limits to the recorded relationships and displaying the details of any relationship which falls outside the allowed limits and predicating the timely required preventative maintained schedule for the equipment (10).