Often, maintenance departments invest in good quality Bolts and Nuts (Grade 8), but neglect to do the same with flat washers. The importance of a good washer cannot be overstated. If you use a typically thin Grade 2 (or worse) flat washer under the bolt head of the hold-down bolts of your machine, this washer will easily be distorted or warped into the hole in the foot upon tightening the anchor bolt. This is particularly true if the difference in shank diameter of the bolt and hole diameter in the foot is significant. This will often be the case when the hole in the foot has been enlarged to overcome a bolt-bound problem. The result of having “dished” washers is that when the anchor bolts are tightened after completing the alignment, the washers will try to center themselves in the hole in the foot and in doing so will pull your machine out of alignment again. This effect is virtually impossible to overcome, resulting in a badly misaligned machine after you just did a good alignment!
Solution: Always discard warped washers and use high quality thick flat washers that will not distort or warp into the hole. This will allow the washers to do their job of supporting the bolt head’s load on the surface of the foot.
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Alignment, Maintenance Tips by Alan Luedeking CRL CMRP