The belly of your electric motor that is!
During the OJT portion of a training class, at an Omaha NE client, I ran into a most extreme case of soft foot. The customer told me they had a motor/pump set that they could not align no matter what. This was a 100 HP electric motor driving a water pump that supplied water to the top floors of a children’s hospital. The class decided to do a simple alignment check when we got to the equipment.
We found the alignment to be close but not quite in tolerance Vertically (Angularity of 0.9 mils/inch, Offset of 9.0 mils) and about twice the 1800 RPM tolerance Horizontally (Angularity of 1.4 mils/inch, Horizontal Offset of 7.8 mils).
The class proceeded to perform the pre-alignment steps, that’s when things got weird. Upon loosening the motor hold down bolts, we noticed very loose shim packs and performed an obvious soft foot check.
They found that the shims under all four feet were loose. Hmmm. After removing all of the shims, we measured .030” or more of obvious soft foot at all four feet! One foot had a .065” gap between it and the base!! It was obvious that something was very wrong here. We initially thought that the motor base was warped or perhaps the motor case itself was warped. After examining the whole situation, we discovered there was debris under the motor belly, a lot!
There were large chunks of cement and mortar under the motor case holding it completely off of the baseplate and to top it off the shims were painted down to the base. The photos show the cement we dug out from under the motor.
After tilting the motor to the side, we were able to use a hammer and chisel to remove the cement chunks and painted on shims.
After almost an hour of chiseling, we had the motor sitting flat on all four feet and we were able to proceed with our precision alignment.
Lesson learned? Check under the motor belly and make sure there is no garbage!