Page 138 - Rotating Machinery Pratical Solutions to Unbalance and Misalignment

Rotating Machinery: Practical Solutions

and recorded. Generally, these old shims should be discarded, and
the alignment process started from scratch. Once a solid alignment
program is in place in your plant, this may not be required.

VERTICAL ALIGNMENT

When dealing with cut shims (cut from stock), or stamped
shims, extreme care should be exercised to assure no burrs exist.
All shims and shim stock to be used in the alignment process must
be measured with a micrometer to verify their thickness. In addi-
tion, no more than three shims should be placed under any ma-
chine foot. This may require obtaining special shim stock, or
perhaps machining spacers. However, this will eliminate most of
the possibility of uneven shim crush that can destroy any align-
ment attempt.
Properly torque down all hold-down bolts and take an initial
set of readings as outlined previously. As a word of caution, ob-
serve the dial indicators to assure you know which way they
moved. Often, they will start in one direction and then reverse and
read the opposite. A large positive reading can be mistaken for a
small negative reading. Once again, return the indicators to the
starting position to assure the readings repeat. If the numbers
repeat and you rotated the equipment in its normal operational
direction, and you did not go past the 6 o’clock mark and reverse,
you are ready to determine the required vertical corrections.
Some people find the graphical method easier to use than the
calculator, while others prefer the calculator to the graph. How-
ever, it is highly recommended that both methods be used to as-
sure the proper corrections are made. Both methods require only
about 2 to 3 minutes each, once you have mastered them, or at
least lost the fear of them.
Both methods are capable of accuracy of better than 1/10 th
mil, but no one would attempt such an alignment; besides, 1/10 th
shims are hard to find. The point is that accuracy to within ±1 mil
will assure an exact alignment and long equipment life. Be sure