December 2018 – EFFICIENT PLANT
The recently released Alignment Standard (ANSI/ASA S2.75-2017) from the American National Standards Institute, Washington (ansi.org) took nearly three years to develop. A committee of alignment experts discussed every aspect from safety procedures to the mathematics involved in defining the new standard. Alan Luedeking, CMRP, CRL, of Ludeca Inc., Miami (ludeca.com) a member of that committee, has been involved in the development of alignment standards for significantly longer than three years.
Luedeking remembers the “old days” well. Back then, personnel simply aligned components to the best of their abilities with straightedges or dial indicators. “Those alignments,” he said, “usually weren’t that good, due to sag, span limitations, obstructions to rotation, or whatever. But you did the best you could, and that was good enough because it was all you could do.”
In 1982, Ludeca introduced the world’s first computerized dial indicator alignment system (from the now-defunct Industrial Maintenance Systems Inc.), followed in 1984 by the world’s first laser-alignment system. With the improved measurement resolution and accuracy afforded by the laser sensor, a more precise definition of what constituted a good alignment became necessary. So, according to Luedeking, after poring through the sparse alignment literature that existed, Ludeca developed tolerance tables for short and spacer couplings, which, for lack of anything better, end users readily accepted. “Over time,” he noted, “these tolerance values came to be accepted as the U.S. industry standard and were adopted as the official tolerance standard by various corporate and government entities, including NASA and the U.S. Navy.”
So what are alignment tolerances, and why are they important? As Luedeking described them, “Tolerances exist because absolute perfection does not. No matter how hard you try and how long you work, you will never get a shaft alignment absolutely perfect.” He offered the following detailed discussion as to why, along with some expert advice on the meaning of the new standard and how it can help you improve your operations. Read the entire article “Alignment Tolerances Carved in Stone”
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