What is ‘soft foot anyway?

A gap between one foot of a machine and the foundation generally is referred to as “soft foot.” A pump or motor typically has four feet and generally rests on three, leaving a gap under the fourth. Recall from high-school geometry that three points determine a plane, which is why dairy-farm milking
stools only have three legs. A soft foot left unshimmed means that a machine frame will distort from its resting position as the hold-down bolts are tightened to secure it in place. This distortion
binds the shaft and preloads the bearings. The latter is one of the leading causes of premature bearing failure. Thus a soft-foot check is vital to the pre-alignment process. Keep in mind that there are different kinds
of soft foot. In its simplest form, a foot can either be parallel or bent. It’s relatively easy to locate a parallel foot (think of it as a short leg) and correct for it. A bent foot is more difficult to fix. One of the benefits of a sophis ticated laser alignment system is that it will have a soft-foot “wizard,” or diagnostic routine, built into
the firmwear to determine if this problem exists and if it must be addressed immediately to assure
satisfactory alignment.