When establishing an effective maintenance program, one must determine not only which Preventive Maintenance (PM) routines to accomplish, but how often should they be done. The answer to this question would seem on the surface to be quite simple and, in fact, one proven theory is that the PM to Corrective Maintenance (CM) work order ratio should be about 6 to 1. This theory assumes that the PM inspections should reveal some type of corrective work that should be completed on an asset on average every 6 times it is accomplished. The assumption is that, if the ratio is greater than 6:1 you are performing the PM too often; if the ratio is less then 6:1, you are not performing it often enough. (The "6 to 1 Rule", proven by John Day, Jr., Manager of Engineering and Maintenance at Alumax of South Carolina, during the period when Alumax of South Carolina was certified as the first "World-Class" maintenance organization).

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