Handbook Of Shaft Alignment Episode 2 Part 4 pot

Next, at the intersection of the graph centerline and the point where the dial indicatorhas captured the smallest reading, plot a point above or below this intersection one-half of the t

reading Draw a line from the point on the graph where the dial indicator capturedthe reading to the outboard end of that shaft Remember, whatever shaft the dialindicator has captured the readings on, that is the shaft that will be drawn on thegraph paper Figure 10.9 shows an example of plotting a pump shaft onto the sideview alignment model.

3 Next, at the intersection of the graph centerline and the point where the dial indicatorhas captured the smallest reading, plot a point above or below this intersection one-half

of the top to bottom or side-to-side dial indicator reading If the bottom (or side)reading was negative, place a point half of the bottom (or side) reading from thegraph centerline toward the top of the graph If the bottom (or side) reading waspositive, place a point half of the bottom (or side) readings from the graph centerlinetoward the bottom of the graph (the same as in the point to point modeling techniques).Lay a straightedge from the point on the graph centerline where the bracket was heldthrough the point on the graph where the dial indicator captured the reading Draw aline from the point on the graph where the dial indicator captured the reading to theoutboard end of that shaft Figure 10.10 shows an example of plotting a motor shaftonto the side view alignment model

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Scale:

30 mils

To select the appropriate up and down scale factor, start with the shaft that had

the larger of the two bottom readings In this example, it is the pump shaft Pick

an up and down scale factor that will keep the entire length of the pump shaft

within the boundaries of the graph paper Usually this scale factor will keep the

motor shaft (which has the smaller bottom reading) within the boundaries of the

graph paper also.

Scale off half of the bottom reading on the pump here (where the dial indicator took the

reading on the pump shaft)

Then draw a line from here (where the bracket was located on the motor shaft and the graph centerline) through the scaled off point here

The reading is negative so start at the graph centerline and plot

up half this amount (28 mils)

FIGURE 10.9 Plotting a pump shaft onto the side view alignment model

Notice that there is a consistency to this plotting technique If the top to bottom orside-to-side dial indicator reading is negative, plot half of the reading toward the top ofthe graph paper, for either shaft If the top to bottom or side-to-side dial indicatorreading is positive, plot half of the reading toward the bottom of the graph paper, foreither shaft.

The process for plotting the shaft in the top view is the same as it is in the side view Asdiscussed in Chapter 8, one of the cardinal alignment modeling rules is to zero theindicator on the side that is pointing to the top of your graph paper Refer to Figure 10.7where it states ‘‘view looking east.’’ Therefore, when looking at our drive system fromabove (i.e., the top view), the direction pointing to the top of the graph paper must be east.Figure 10.11 shows how the pump shaft is plotted in the top view and how the east sidereadings were zeroed to extract the west side readings on each shaft from the complete set

of reverse indicator measurements Figure 10.12 shows how the motor shaft is plotted inthe top view

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Scale:

30 mils

Construct the position of the motor shaft based on the bottom reading

captured by the dial indicator as shown

If the graph is stripped away, here are

the exaggerated relative positions of the

motor and pump shaft centerlines

The goal is to bring these shafts into alignment with each other.

How many possible ways can you move these two shafts so they come in line with each other?

Answer: There are an

infinite number of ways to align two

shafts when you consider that they are both movable!

FIGURE 10.10 Plotting a motor shaft onto the side view alignment model

10.4 MODELING THE REVERSE INDICATOR METHOD USING

THE LINE-TO-POINT TECHNIQUE

There is an alternative method to graphing or modeling reverse indicator readings There aretwo advantages of this technique as opposed to the point-to-point method:

. Somewhat easier to model multiple element drive trains where reverse indicator readingswere captured at two or more flexible couplings

. Regardless of whether you have an asymmetrical or symmetrical bracket arrangement,the points where the brackets are being clamped to the shaft are not relevant, only thepoints where the dial indicator readings are being captured are required

There are six pieces of information that you need to properly construct the shaft positionsusing this technique

FIGURE 10.11 Plotting a pump shaft onto the top view alignment model

1 The distance from the outboard-to-inboard feet (bolting planes) of the first machine.

2 The distance from the inboard bolting plane of the first machine to the point

on the shaft where the dial indicator is capturing the rim readings on the firstmachine

3 The distance from where the dial indicator is capturing the rim readings on the firstmachine to the point where the dial indicators are capturing the rim readings on thesecond machine

4 The distance from where the dial indicator is capturing the rim readings on the secondmachine to the inboard bolting plane of the second machine

5 The distance from the inboard-to-outboard feet (bolting planes) of the second machine

6 The eight dial indicator readings taken at the top, bottom, and both sides on both shaftsafter compensating for sag (i.e., what a perfect, ‘‘no sag’’ bracket system would havemeasured)

Accurately scale the distances along the length of the drive train onto the graph centerline

as shown in Figure 10.13

The procedure for plotting the line-to-point reverse indicator technique is as follows:

1 Select one of the two machinery shafts and draw one of those shafts on top of the graphcenterline Figure 10.14 shows an example where the motor shaft was initially placed on

FIGURE 10.12 Plotting a motor shaft onto the top view alignment model

the graph paper centerline and the pump shaft position was plotted from the reverseindicator measurements Figure 10.15 shows an example where the pump shaft wasinitially placed on the graph paper centerline and the motor shaft position was plottedfrom the same reverse indicator measurements.

2 Start with the top to bottom or side-to-side dial indicator readings on the other shaft(i.e., the one you did not draw on the graph centerline)

3 Plot the other shaft centerline position by starting at the intersection of the graphcenterline and the point where the dial indicator was capturing the readings on theother shaft If the bottom (or side) reading was negative, place a point half of the bottom(or side) readings from the graph centerline toward the top of the graph If the bottom (orside) reading was positive, place a point half of the bottom (or side) readings from thegraph centerline toward the bottom of the graph (the same as in the point-to-pointmodeling techniques) Do not draw any lines yet!

4 Next, start at the intersection of the graph centerline and the point where the dialindicator was capturing the readings on the shaft that was drawn on top of the graphcenterline If the bottom (or side) reading was negative, place a point half of the bottom(or side) readings from the graph centerline toward the bottom of the graph If thebottom (or side) reading was positive, place a point half of the bottom (or side) readings

15 in 5.5 in 7 in. 10 in. 14.5 in.

Scale:

5.5 in 7 in 10 in 14.5 in.

0 50 + 10

30 mils Draw the motor shaft directly on the graph paper centerline

Plot half of the bottom reading (14 mils) here

Plot half of the bottom reading (28 mils) hereFIGURE 10.14 Side view example where the motor shaft was initially placed on the graph papercenterline and the pump shaft position was then plotted

Scale:

30 mils Draw the pump shaft directly on the graph paper centerline

Plot half of the bottom reading (14 mils) here

Plot half of the bottom reading (28 mils) hereFIGURE 10.15 Side view example where the pump shaft was initially placed on the graph papercenterline and the motor shaft position was then plotted

from the graph centerline toward the top of the graph (opposite of the point-to-pointmodeling technique).

5 These two points marked on the graph at the dial indicator reading points define the line

of sight (i.e., the centerline of rotation) of the other shaft Draw a straight line throughthese two points from the coupling end to the outboard end of the other shaft

To make your alignment corrections, refer to the Section 8.4.6 and Section 8.4.7

BIBLIOGRAPHY

‘‘Boiler and Machinery Engineering Report—Shaft Alignment for Rotating Machinery,’’ Section 4.0,

#4.26, October, 1989, American Insurance Services Group, Inc., New York

Blubaugh, R.L and Watts, H.J., Aligning rotating equipment, Chemical Engineering Progress, 65(4),

1969, 44–46

Dodd, V.R., Total Alignment, The Petroleum Publishing Company, Tulsa, OK, 1975

Dreymala, J., Factors Affecting and Procedures of Shaft Alignment, Technical and Vocational ment, Lee College, Baytown, TX, 1970

Depart-Durkin, T., Aligning shafts, Part I—measuring misalignment, Plant Engineering, January 11, 1979.King, W.F and Peterman, J.E., Align Shafts, Not Couplings!, Allis Chalmers Electrical Review, 2ndQuarter, 1951, pp 26–29

5 in.

Scale:

20 mils

Draw the pump shaft directly on the graph paper centerline

Plot half of the west reading (10 mils) here

Plot half of the west reading (18 mils) here

East Top view

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+24 –24 0

FIGURE 10.16 Top view example where the pump shaft was initially placed on the graph papercenterline and the motor shaft position was then plotted

Murray, M.G., Alignment Manual for Horizontal, Flexibly Coupled Rotating Machines, 3rd ed., Murrayand Garig Tool Works, Baytown, TX, 1987.

Murray, M.G., Choosing an Alignment Measurement Setup, Murray and Garig Tool Works, Baytown,

TX, personal correspondence, October 12, 1979

Nelson, C.A., Orderly steps simplify coupling alignment, Plant Engineering, June 1967, pp 176–178.Piotrowski, J.D., Alignment techniques, Proceedings Machinery Vibration Monitoring and AnalysisMeeting, New Orleans, LA, June 26–28, 1984, Vibration Institute, Clarendon Hills, IL.Piotrowski, J.D., The Graphical Alignment Calculator, Machinery Vibration Monitoring and Analysis,Vibration Institute, Clarendon Hills, IL, 1980

Samzelius, J.W., Check points for proper coupling alignment, Plant Engineering, June 1952, pp 92–95.Two Step Dial Indicator Method, bulletin no MT-SS-04-001, Rexnord, Thomas Flexible CouplingDivision, Warren, PA, 1979

Yarbrough, C.T., Shaft Alignment Analysis Prevents Shaft and Bearing Failures, Westinghouse Engineer,May 1966, pp 78–81

11 Face and Rim Methods

Perhaps the first dial indicator technique used to align rotating machinery shafts is the faceand rim or face–peripheral method shown in Figure 11.1 It is not entirely clear who initiallyused this technique or when and where it was employed to align rotating machinery shafts butthis method is frequently referred in machinery installation manuals and coupling installationinstructions and is still practiced by personnel who align machinery It is similar to the waymachinists center and square work pieces in lathes and mills and undoubtedly came frommachining practices during the dawn of the industrial revolution

As shown in Figure 11.2, the face readings can be taken on either side of the coupling hub(or an object affixed to the other shaft) The accuracy of this method is directly related to thediameter the face readings are taken on as demonstrated in Figure 11.3 The larger the diameter

of the face reading sweep, the more accurate this method becomes Assuming that both shaftscan be rotated, the face diameter can be increased by attaching an object to the one shaft andthe face indicator placed against that object as shown in Figure 11.4

Advantages

1 This is a good technique to use in situations where one of the machinery shafts cannot

be rotated or it would be difficult to rotate one of the machinery shafts (see also Chapter 12)

2 Many people who use this method understand that the rim (or diametral surface) dialindicator shows centerline offset or parallel misalignment and the face indicator indi-cates that an angular misalignment condition is present

3 This is a good method to use when the face readings can be taken on a fairly largediameter (typically 8 in or greater) This method begins to approach the accuracy of thereverse indicator technique whenever the diameter of the face readings equals or exceedsthe span from the bracket location to the point where the rim indicator readings arebeing captured in the reverse indicator method

Disadvantages

1 Not as accurate as the reverse indicator method if both shafts can be rotated andparticularly if the face measurements are taken on diameters less than 8 in

2 If the machinery shafts are supported in sliding (plain or sleeve) bearings, it is very easy

to axially float the shafts toward or away from each other when rotating the shaftsresults in bad or inaccurate face readings (see Section 6.10)

3 Bracket sag must be measured and compensated for

11.1 MATHEMATICAL RELATIONSHIP IN MACHINERY ALIGNMENT

Figure 11.8 shows the mathematical relationship between the machinery dimensions and thedial indicator readings captured using the face–rim method The equations will solve for themoves that need to be made to correct the misalignment condition (i.e., bring the shafts into a

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collinear relationship when off-line) on one or the other machine case It is an either–orcondition If you decide to keep the driver stationary, you solve for the moves on the drivenmachine or vice versa.

11.2 SIXTEEN-POINT METHOD

A method similar to the face–rim method called the 16-point method is frequently used onrotating machinery connected together by rigid rather than flexible couplings The generalprocedure is illustrated in Figure 11.9

This method is typically used where one shaft is supported in two bearings and the othershaft is supported in one bearing on the outboard end The coupling flanges have a recessed(rabbeted) fit The assumption made when performing this technique is that there is onlypure angular alignment present (i.e., no centerline offset) and that the flange faces are

• PROCEDURE •

1 Attach the alignment bracket firmly

to one shaft and position the

indicators on the face and diametral

surface of the other shaft

(or coupling hub).

2 Zero the indicators at the twelve o'clock

position

3 Slowly rotate the shaft and bracket

intervals stopping at the three, six, and

nine o'clock positions Record each

reading (plus or minus).

4 Return to the twelve o'clock position to

see if the indicator(s) re-zero.

5 Repeat steps 2 through 4 to verify

the first set of readings.

Rim dial indicator

Face dial indicator

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Indicator readings log

Rim or peripheral readings

Face readings

FIGURE 11.1 Face and rim method and procedure

perpendicular to the centerlines of rotation The flange bolts are loosened, the shafts ated just slightly, insuring that the flange faces are still indexed in the recess, and a series offace readings are taken at four points around the flange faces at the twelve, three, six, and nineo’clock positions No rim readings are taken.

“Front” side face reading starting “plane”

Indicator stem will get pushed in when it gets to the bottom resulting in a positive (+) reading.

r o

t a

e

FIGURE 11.2 Face readings can be taken on the front or back sides

with a dial indicator, feeler gauge, snap gauge, or an inside micrometer is used to take theface measurements.

11.4 PROBLEMS WITH TAKING FACE READINGS

When performing any method where face readings are taken, measurement inaccuracies andinconsistencies can occur if the shafts that are rotated, move toward or away from each other,during the process of capturing the measurements This can occur very easily if the shafts aresupported in sliding or journal-type bearings

The first indication that this is occurring is if the dial indicator (or any measurement sensor)does not return to zero after a 3608 sweep is made It is therefore suggested that at least twocomplete sets of readings are taken to see if there is repeatability in the measurements at each

908 location If the measurements do not repeat within 1–2 mils after two sweeps are madeand you suspect that the shafts are indeed moving toward or away from each other, then youcan try one of the following three procedures to improve the accuracy of the measurements

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