Page 129 - Rotating Machinery Pratical Solutions to Unbalance and Misalignment

Advanced Machine Alignment

can cause major problems. Large and obvious defects are usually
corrected when they are detected. However, the smaller seemingly
insignificant things are too often ignored.

THE ALIGNMENT FIXTURE AND BAR SAG

One of the first steps in any alignment process is to deter-
mine how to set up a fixture that will allow you to take the re-
quired measurements. In aligning two shafts, the readings are
taken from the stationary shaft to the adjustable shaft, across the
coupling. Always mount the fixture to read from the STATION-
ARY equipment to the ADJUSTABLE equipment!
Once you have set up a suitable fixture to allow attaching the
two dial indicators to read a rim and a face reading across the
coupling, the fixture should be removed without disturbing the
distances being measured. Prior to removing the fixtures, their
exact location should be marked on the shafts, so they can be
reinstalled in the same location.

Rim Indicator Reads
Plus Bar Sag @
12 O’clock

Rim Indicator Reads
Set to Zero @
6 O’clock

Figure 8-4. Measuring Bar Sag