|Mis-alignment can be
the most usual cause for unacceptable operation and high
vibration levels. New facilities or new equipment installations
are often plagued by improper alignment conditions.
Many methods are used to align machinery. The simplest method
is using a straight edge to bring the machines into rough
alignment. A rough alignment is necessary due to the range
limitations of the dial indicators. A popular method used for
years and is still in use today is the rim and face method. This
method produces acceptable results, but is less accurate than
the reverse dial indicator method covered in this application
note. Additionally, reverse dial alignment does not require
removal of the coupling to collect data.
WORKING WITH DIAL INDICATORS
Dial indicators are available in many physical sizes and ranges.
most alignment applications the smaller sized indicators should
be used to reduce indicator bar sag. Dial indicators should be
chosen that have a range of 0.100 inch and accurate to 0.001
readings, and many other types of readings, are expressed in
several units. A reading of 1/1000" is equivalent to 0.001 inch
and is commonly expressed as 1 mil.
A common convention used when reading dial indicators is that
when the indicator plunger is moved toward the indicator face
the display shows a positive (+) movement of the dial needle by
sweeping the needle clockwise. As the plunger is stroked away
from the face a negative (-) reading is displayed by sweeping
the needle counterclockwise. Negative movements of the dial
needle may be confusing if the indicator is not observed
carefully throughout the rotation cycle of the machine shafts.
Another convention to employ is that when all readings are
recorded, they should be interpreted recorded by viewing from
the stationary machine to the moveable machine. This convention
is necessary to distinguish right from left readings during data
collection process and will be applied when the calculations and
graphs are made to decide upon the actual moves required at the
Prior to any alignment activity an extensive list of items must
be checked to ensure acceptable results. The obvious item
involves ensuring that the machine shaft axes are roughly
aligned within 50 mils. Other inspections should include:
- The foundation base plate is adequate and that grout has
been installed properly.
- All machine feet are in full contact with the foundation
baseplate or supports.
- Piping is not inducing strain onto the machine cases.
Piping should be aligned to within " of their flanges.
- The machine feet bolt holes have enough clearance to
conduct alignment activity.
- The coupling faces are axially aligned; the axial
spacing between the coupling faces as correct.
- Coupling radial runout is less than 2 mils.
- Coupling face runout is less than ½ mil.
- The moveable machine has as initial shim pack installed;
the shim pack should be comprised of one thick spacer and
one or two smaller shims. Too many shims will act like a
spring causing additional problems.
- The required amount of cold offset compensation is
available; this may be available from the machine
- The alignment bracketry is appropriate to the activity
MOUNTING DIAL INDICATORS
Many commercially available reverse dial indicator alignment
kits have modular bracketry which can encompass the majority of
applications. However, some applications will require a custom
bracket. Regardless of the type of bracket used, the amount of
bracket or bar sag should be documented so that this information
is available to be included in the calculations.
Bar sag can be easily documented by installing the bracket
and dial indicator, in the identical
to be used on the machine, onto a pipe. Zero the indicator while
it is on top of the pipe. Now rotate the pipe 180 so that the
indicator is at the bottom position. The indicator will now
display twice the amount of bar sag.
Mounting the indicator onto the bracketry should be performed
carefully so that the indicator plunger axis is perpendicular to
the machine shaft axis to ensure accurate readings. An error of
only 10 will produce a 16% error in the indicator reading.
After the bracketry is firmly attached and the dial indicators
are installed, four reading locations are required. These
along the circumference of the shaft or coupling in the path of
the indicator plunger. They are top, bottom, right, and left.
These location are to be separated by 90 of shaft rotation.
Marking these locations with an indelible marking pen is
adequate. Another approach is to use a common two axis trailer
level attached to a coupling face or other surface to determine
when the shaft has been rotated 90 . Placing four pieces of tape
equally spaced around the circumference of the shaft will work,
as long as the tape is not in the path of the indicator plunger.
Before any readings can be taken the dial indicators must be
set. A simple test of rotating the machine shaft through an
entire 360 sweep will verify that the indicator plunger tip is
in complete contact with the shaft. When the indicator is at the
top location the indicator should be reset to display zero. This
is accomplished by rotating the outer bezel of the indicator
until the dial face, which is attached to the bezel, shows "0"
under the needle.
Collecting the data is simply a matter of rotating the
machine shaft in 90 increments and noting the dial indicator
readings with their signs (+ or -).
If only one dial indicator setup is available, the bracketry
must be relocated to the other coupling or shaft and the sweep
should be repeated. Remember, that all readings should be
collected while observing from the stationary machine to the
moveable machine to maintain right and left consistency.
Collecting the necessary data is simple enough, but will be
entirely useless without some form of accuracy verification.
Each time the dial indicator is rotated to the top location it
should display a reading of zero. If it does not then something
has moved during the rotation: indicator, bracket, clamping
mechanism, machine. Correct the problem and start over.
test, which can be performed as the data is collected, is to
verify that the sum of the top and the bottom readings should
equal the sum of the left and right readings.
As the dial indicator is swept around the circumference of a
coupling or shaft it displays twice the difference between the
projected centerline of the indicator's attachment point and the
measured shaft centerline. This argument applies for both the
vertical and horizontal readings.
Thus, the sum of the vertical and horizontal readings must be
divided by two to represent the actual differences in the two
shaft centerlines. Remember to observe the signs of the
indicator readings closely to prevent errors in these
Two vertical offset numbers and two horizontal offset numbers
will be obtained; one set representing the readings while the
bracketry is installed on the original shaft and another set
representing the readings while the bracketry is installed on
the second shaft.
Horizontal calculations sometimes present some confusion
because one side does not start at zero. Adding or subtracting
the magnitude of the right side reading to both sides will force
the right side to zero.
GRAPHING THE RESULTS
Presenting the calculated results in a graphical format will
assist in visualizing the required machine moves. Although any
size graph scale is adequate for this process, expanding the
scale as large as possible will improve the accuracy of the move
calculations because the measured differences of the shaft or
coupling centerlines are projected out to the locations of the
moveable machine's feet.
As the figure shows, two sets of dial indicator readings are
collected. The readings taken on the stationary coupling are
located above the stationary machine (pump) and the readings
collected on the moveable coupling are located above the
moveable machine (motor). When plotting these readings start
with the stationary readings and then proceed to plot the
Directly plotting the measured readings will display a
representation of the existing mis-alignment. The desired
alignment condition can be drawn onto the graph. The desired
condition should include any offset compensation so that when
the machine train is operating under normal conditions the
alignment is within acceptable tolerances.
a graph scale large enough to provide sufficient accuracy when
all calculations are completed. Lay out the physical dimensions
of the machine train and show the collected data on the graph
the graph show the locations of the machine feet, the dial
indicator sweep plane, and the location of the power
transmission points. Note that for this example, the power
transmission points do not coincide with the sweep path of the
actually plotting the vertical offsets, start with the
stationary set first. Remember that the data collected
represents twice the actual differences between the shaft
centerlines. A positive result is plotted above the line
representing the stationary machine centerline. When plotting
the moveable machine readings a rule of thumb is that opposite
signs are plotted on the same side of the stationary machine
centerline on the graph.
For simplicity's sake, the horizontal readings are plotted
separately in this example. A better approach is to combine the
vertical and horizontal plots onto a single plot.
as was performed for the vertical plots, the horizontal plot has
a scale reference, the field collected data, and other important
dimensions shown for completeness. Also, note that the
stationary machine centerline is labeled right and left.
same process of plotting the data is followed, but note that the
field collected data has been adjusted so that the right side
readings have a magnitude of zero to make plotting easier. The
opposite sign rule of thumb also applies for horizontal
After all the data has been plotted, the required corrections
of the moveable machine can be obtained directly from the graph.
Obtaining this information in this manner eliminates
mathematical errors possible using other methods. Graphical
presentations allow experimentation and study of many
possibilities for correcting alignment.
this example, the motor outboard feet need to be lowered 17 mils
and the inboard feet must be lowered 12.5 mils for a perfect
alignment with the pump.
This alignment condition assumes that the pump does not
thermally grow as it operates. If some thermal growth is
anticipated, then this information can be plotted on the graph
as an offset of the stationary machine's centerline and
appropriate moves of the moveable machine can be obtained by
projecting the stationary machine's centerline over to the
moveable machine's location.
The horizontal movements for this example are 35.5 mils to
the left at the motor outboard and 16.5 mils to the left at the
inboard motor feet.
Graphically plotting the results makes the movement
computations easier, but prior to any moves the following topic
"ACCEPTANCE TOLERANCE" should be considered because the existing
alignment may be acceptable. Re-alignment of a machine with
acceptable alignment conditions is a waste of time and is only a
practice exercise at best that may produce a worse alignment
Determining whether the existing alignment condition is
acceptable or the actual machine moves resulted in an acceptable
alignment condition can be quantified by referencing the chart
at the end of this application note. This chart may be applied
to all machine and coupling types. The chart takes into account
the coupling span and the machine operating speed.
The key to applying the chart is to determine the locations
at which the power is transmitted. For gear type couplings the
power transmission points are the gear teeth on each coupling
half. For diaphragm type couplings the power transmission points
are the coupling faces.
The locations of the power transmission points should be
noted on the graphical plot. Depending upon the data collection
method and the coupling type,. the power transmission points may
not coincide with the coupling faces or the dial indicator sweep
path. Following are the calculations necessary to determine the
Alignment Accuracy = Maximum (X, Y)/D
X = ( XV2 + XH2 )½
Y = (YV2 + YH2 )½
XV and XH = amount of offset, vertically and horizontally, at
the power transmission point on the stationary machine.
YV and YH = amount of offset, vertically and horizontally, at
the power transmission point on the moveable machine.
Maximum (X, Y) = larger of X or Y, calculated above.
Plotting the resultant alignment accuracy on the chart will
determine whether the existing alignment condition is acceptable
or whether the proposed correction moves will produce acceptable
MOVING THE MACHINE
Moving a machine is, in many cases, difficult due to their size
and weight. Extremely heavy machines, such as power plant
generators will require hydraulic jacks. Most other machines can
be moved using jacking screws, which are rigidly attached to the
foundation base plate, and pry bars to lift the machine.
Prior to any horizontal move a dial indicator should be
installed to monitor each foot along one side of the machine for
horizontal movements. Vertical movements will require an
indicator on each foot on both sides of the machine. Vertically
oriented indicators should be observed as the machine foot bolts
are re-torqued. The displayed indication should not change by
more than 1-2 mils, indicating that all feet are supporting the
machine equally. Finally, after the bolts are re-torqued the
jacking bolts should be backed out so that they do not influence
the natural thermal growth as the machine heats. Other machines,
such as gear boxes, turbines, and compressors should have dowel
pins installed at strategic locations to control the thermal
The best choice for shim material is stainless steel. This
material is very stable and is easy to maintain. Carbon steels
should be avoided because it will rust and eventually compromise
the machinery alignment. Synthetic or plastic shim material
should be avoided for industrial applications because it is
easily damaged and under heavy load will deform which
compromises the alignment condition.
The shims used for industrial applications should be large
enough to adequately support each foot. Commercial shims are
available in various dimensions. These shims are precut and
dimensioned to standard thicknesses which are labeled on a small
tab. These shims are easy to install and are difficult to mix
up. If shims are manufactured in the field they should be large
enough to support the machine foot and all edges should be
smoothed to eliminate burrs. Kinked or otherwise damaged shims
should be discarded and new ones obtained. The shims, the base
plate surface, and bottoms of the machine feet should be clean
and free of defects prior to installing any shims.
WHICH MACHINE MOVES?
Generally, the stationary machine has certain constraints which
make in impractical to move it. Pumps have rigid piping
attached, generators have complex cooling systems, and gear
boxes are relatively sensitive to any orientation other that
flat and level. When these machine types are moved the attached
systems must be relocated to eliminate sources of strain.
Multiple case machine trains, such as dual compressors driven
by one turbine, pose another problem. All three machine shafts
must operate co-linearly to function efficiently. By studying
the graphical plot of the current alignment and the desired
alignment it may prove most effective to move the center machine
case, instead of moving two or three machines.
- Pre-alignment Conditions
- Shim Materials
- Indicator Bracket Sag
- Graph Materials