May 10, 2013
Bolt Bound? No Alternate Move Calculator? No Problem!
By Brad Case
Previous blogs have discussed several different solutions for solving Base Bound & Bolt Bound conditions when preforming precision laser shaft alignment (Base/Bound Math and Solving Base/Bound Alignment Alignment Problems). Sometimes though, the solution for a Bolt Bound issue is fairly straight forward and what you need to do is right in front of your eyes on the display unit screen.
Recently a Fixturlaser GO Pro training class was checking the alignment of a small 3600 RPM, 10 HP electric motor & Durco Centrifugal Pump set. The “As Found” results revealed both the vertical and horizontal angular misalignment to be more than 5 and 7 times the allowable tolerance respectively. The Offset misalignment was not too terrible.
Tolerances for 3600 RPM are no more than +/- 0.5mils/1” angular and +/- 2.0 mils offset misalignment
After checking for soft foot the class set about to perform a Verti-Zontal Compound MoveTM by first removing shims, as indicated, to correct the Vertical misalignment leaving the hold down bolts loose, then going live with the GO Pro to correct the Horizontal misalignment.
As the motor was moved horizontally the angular coupling value came into tolerance, however the offset coupling tolerance stopped short at -13 mils. There was freedom of movement with the back feet of the motor but the front feet where bolt bound by 10 mils and no adjustment of the motor could get the offset misalignment in tolerance.
Alternate solutions where discussed, the motor/pump base was composite with threaded inserts so using smaller bolts and nuts was not an option. While discussing the option to enlarge the motor feet, a mechanic said “What a minute! All we need to do is loosen the pump and move the coupling end the opposite direction the display screen shows we need to move the motor.” He was correct.
That is exactly what they did, with one slight push to the front feet of the pump the Offset Coupling Value came in tolerance, a slight touch up to the rear motor feet brought the Angular Coupling Value back into tolerance. After tightening all hold down bolts they re-measured with the GO Pro and where finished after one Verti-Zontal Compound MoveTM. Total time from out of the box to final results about 30 minutes!
Moving the pump is ok but can cause a pipe strain issue that will need to be addressed.
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I would agree with Jesse’s comment. Pipe strain can cause problems too. But, if you can push the pump over by hand, or with a small pry bar, pipe strain will be minimal. I have loosened pumps up, and they moved in the right direction by themselves! It’s a much easier fix than flipping a motor upside down, and drilling out the feet. That can cause as much of a problem as boing bolt bound.
If it takes a come-along to hold it in place, you’re probably causing some strain somewhere. Otherwise I think you’re generally OK. Most of the moves on the stationary end up being pretty small.