Practical Solutions to Machinery and Maintenance Vibration Problems
Chapter 5, Unbalance
Section 18, Improper Surface-to-Surface Fit Due to Stretched Threads
Similar to the above, previously assembled machinery may have had a small portion of screw-hole thread pulled above the surface of the part. Most of the time there is no difficulty as the mating part's hole diameter is large enough to clear the raised metal. However, in a percentage of situations, a few mils of the raised metal causes a bad fit between mating parts. The craftsperson should automatically and routinely rub a flat abrasive stone against the flat top surfaces of the bolt holes (such as bolt holes in a machine's sole plate or the bolt holes of any mating surfaces that can result in unbalance if not properly assembled). A few quick rubs per hole will usually be sufficient. For most holes, no high spots of metal are removed, but for about 10 percent of bolt holes, the removed high spot of stretched thread will reveal a shiny spot. Again, the old balancing standards would not require this. Present precision standards do.
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