Page 137 - Rotating Machinery Pratical Solutions to Unbalance and Misalignment

Advanced Machine Alignment

intersect the face line a distance A away. From this point, the cor-
rected face reading is measured off. Again a line is constructed
passing through these two points and extending through the two
foot locations. The result is identical to the result found in the
reverse indicator method: add 4.5 mils to the inboard foot and 13
mils to the outboard foot.
Both of these methods will be explored in detail in this and
the subsequent chapter.

TAKING INDICATOR READINGS

Once soft feet are corrected, machine measurements taken,
the fixture assembled, and bar sag determined, an initial set of
readings can be taken. Be sure to always rotate both shafts to-
gether (in the event the coupling is not made up), and always
rotate the machine in the direction of normal operation. This is
especially true of equipment that has gears or tilt pad thrust bear-
ings.
Never back up to get a reading. If you rotate the fixture too
far, continue around in the same direction until it lines up. For the
vertical alignment readings, the rim indicator is set to the (+) sag
and the face indicator to zero (0) in the 12 o’clock position. The
shafts are rotated to the 6 o’clock position and a set of readings is
taken. To assure the information is correct, continue to rotate the
shafts until they return to the 12 o’clock position, where the indi-
cators should return to their original readings. If the readings do
not repeat within 1/2 mil, the fixture is not securely mounted or
is not sufficiently ridged.
Prior to any actual alignment corrections, several things must
be performed. As with the stationary machine, the adjustable
machine must have its shims, feet, and base plate inspected and
cleaned. Checks for soft feet should be made as was done for the
stationary machine. On the adjustable machine, this should be
performed with all old shims removed. The amount of shims
under each foot should be measured, verified with a micrometer,