Practical Solutions to Machinery and Maintenance Vibration Problems
Chapter 7, Misalignment
Section 4, Machinery Soft Feet
Most craftspeople who align machinery already understand the phenomenon of what is usually called machinery "soft foot." As many vibration specialists have never actually aligned machinery, they may have heard of "soft feet" but may not always understand the result in vibration.
Update separates true machine soft foot from what is called "Foot-Related Resonance." Soft feet can cause increased vibration amplitudes, but not always. Although soft feet does not necessarily magnify machine vibration, it should be reduced for many reasons, including preventing vibration magnification. Understanding soft feet will also help the analyst when working with Foot-Related Resonance.
Although there are many combinations of conditions that produce a soft
foot, most often it is the result of all the shimmed feet not being
in the same plane. The following bottom views show some of the most
common conditions for soft foot:
This textbook contains only part of the information in our Practical Solutions seminar.