Soft Foot; Figure 7-13. Parallel And Angular Soft Foot - Fluke 830 User Manual

Horizontal shaft alignment

Soft foot

Soft foot
Soft foot is the condition of machine frame distortion. Any cause that results in
machine frame distortion when the machine is anchored to its foundation is a soft
foot. Some of the principal causes are:
● Non-coplanar machine mounting surfaces
● Deformed machine frame or feet
● External forces e.g. from connecting pipe or bracketry
● Improper shimming or soiled machine feet
● Too many shims under a machine foot (a maximum of 5 shims should not be
exceeded)
The consequences of forcibly tightening down the feet are deformed machine
frames, bent shafts and distorted bearings. This leads to high vibration and
premature machinery failure.
Soft foot should be checked before aligning the shafts. This can be done quickly
and conveniently with the aid of the Product's soft foot function. With the sensor
and prism mounted on the shaft in the usual way, the system is able to sense any
machine movement when individual machine bolts are loosened. By entering the
machine dimensions, the Product is able to calculate, from shaft movement, by
how much each foot has moved as it is loosened.
Once foot movements have been established, the results are interpreted and
translated into shim thicknesses to be placed under the feet. How straightforward
this is, depends on the type of soft foot present.
Parallel soft foot Angular soft foot

Figure 7-13. Parallel and angular soft foot

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