Page 213 - Machinery Component Maintenance

Machinery Alignment 195

(Total Alignment, Reference 3) describes one such system. Another that
we saw demonstrated provides not only the numerical data, but a dia-
grammatic representation of the machines and their alignment relation-
ship, on a cathode ray tube.
The foregoing electronic systems are popular, and have advantages in
speed, accuracy, and ease of use. They have disadvantages in cost, us-
ability under adverse field and hazardous area conditions, pilferage, sen-
sitivity to damage from temperature extremes and rough handling, and
availability to the field machinist at 2:OO A.M. on a holiday weekend.
They also, for the most part, work mainly with numbers, and the answers
may require acceptance on blind faith. By contrast, graphical methods
inherently aid visualization by showing the relationship of adjacent shaft
centerlines to scale.
Manual calculation methods have the advantage of low investment
(pencil and paper will suffice, but a sliderule or simple calculator will be
faster). They have the disadvantage, some say, of requiring more think-
ing than the programmed electronic solutions, particularly to choose the
plus and minus signs correctly.
The graphical methods, which we prefer, have the advantage of aiding
visualization and avoiding confusion. Their accuracy will sometimes be
lcss than that of the “pure” mathematical methods, but usually not
enough to matter. Investment is low-graph paper and plotting boards
are inexpensive. Speed is high once proficiency is attained, which usu-
ally does not take long.
In this text, we will emphasize the graphical approach. Before doing
so, let’s highlight some common manual mathematical calculations.
Nelson” published an explanation of one rather simple method a num-
ber of years ago. A shortened explanation is given in Figure 5-16. For
our given example, this would work out as follows:

Gap difference: .OO7 in.
Foot distance: 30 in.
Coupling measurement diameter: 4 in.

(30)
(.OO7) X - 0.0525 in.-say .053 in. shim addition beneath
=
(4) inboard feet, or removal
beneath outboard feet, or a
combination of the two, for
a total of .053 in. correction.

Then, using rim measurements, determine parallel correction, and add
or remove shims equally at all feet. Now do horizontal alignment simi-
larly, and repeat as necessary.