Mechanical drive equipment must be selected correctly and operate smoothly with no vibration. Drive shafts must be designed and manufactured with precision to prevent operation near a natural frequency. We have gotten more sophisticated in determining and controlling the natural frequency of drive shafts. As a user, you must be cautious of the supplier you choose for your drive system critical components. Not all manufacturers have a sufficient level of understanding; therefore, any supplier should provide you with the data to support the natural frequency values they publish.