User Manual

Appendix
A-1
A
Foot Pre-Check Types
Foot Pre-Check Measurement Methods – Soft Foot and Frame Distortion
Index (FDI)
Soft foot is a condition where all feet (typically four) of a machine compo-
nent (such as a motor or gearbox) will not rest on the same plane. This con-
dition also exists if the machine baseplate pads (where the machine foot
rests) are not on that same plane. If this condition continues to exist and is
not corrected, two problems will occur.
First, it will be very difficult to align the machine. You will appear to be
“going in circles” trying to move the machine into alignment. Second, but
most important, the machine will not operate properly. The component
was not designed to operate in a bound condition. When this happens,
binding will occur causing stress at the bearings and changing the operating
clearances (inside the component). To prevent binding, you must check all
the feet,
even those on the machine not being moved .
Traditional methods of measuring soft foot conditions included mounting a
dial indicator at the machine foot (similar to Fig 1). The hold-down bolt was
then loosened while the indicator was watched for movement. If the indi-
cator moved more than a predetermined amount (usually 0.003 inch), the
foot required correction. A shim equal to the amount of the indicator move-
ment was then shoved under the foot.
Fig 1
Fig 2