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Soft Foot Measurement – It Really Is Important!

On a recent visit with a power plant the customer asked me to help them align a pump with their new Easy-Laser alignment system. It was a machine they had previously aligned with dial indicators, they thought it was “pretty good”. The initial measurement showed a vertical offset of about 7 mils, so we removed all the shims and measured soft foot. The results seen on the Easy-Laser system were as seen here:

As you can see there was a significant issue. We probed and found gaps under both the indicated feet. The foot showing 32.6 mils showed a parallel gap, the foot showing 22.1 showed an angular gap and required step shimming. Once the soft foot was corrected we continued with the alignment, and achieved excellent results.

In later conversation, I learned that the motors had been too high for the pumps when installed, so the contractor ground down the feet with a wheel grinder! That explains the soft foot issue!

Bottom line, ALWAYS check soft-foot. Not only does uncorrected soft foot make the alignment more difficult, it introduces stresses to the machine that reduce reliability.