Soft foot occurs when rotating machinery is positioned in place on its base, frame, or soleplate, and one or more of the “feet” are not making good contact.

We should care because roughly two-thirds of all rotating machinery have a soft foot problem that contributes to premature asset failure. But most facilities rarely, if ever, check for it.

The most common way to describe soft foot is to compare it to a wooden chair or table with four legs. When one foot is shorter than the rest, the chair will wobble.  A machine with soft foot has feet that do not make point contact with its base in a similar way ─ with similar results of misalignment or machine frame distortion.

The following are the destructive effects of soft foot when it goes undetected:

• The shift of the center line of rotation, which destroys the machine from inside out
• Warping of a machine; when a machine has soft foot, the shaft position can change and shift
• Residual vibration, which loosens the foot bolts over time
• Cyclical fatigue ─ this fatigue occurs in areas of highly concentrated stress and can begin to form crack(s) that spread along the machine housing
• Fretting corrosion ─ the repetitive impact from vibrating loose feet causes and spreads corrosion, potentially damaging the machine base

How often do you check your machinery for soft foot? A recent poll found that 40 percent of maintenance engineer respondents rarely check for soft foot.  If you’re not, you should be.

Learn more about how to detect and correct soft foot by watching this Fluke Accelix Best Practice Webinar on-demand: “A hard look at soft foot: detecting machine frame distortion before it causes major issues.”