For most rotating machines used in the process industries, the trend istoward higher speeds, higher horsepowers per machine, and lesssparing. The first of these factors increases the need for precisebalancing and alignment. This is necessary to minimize vibration andpremature wear of bearings, couplings, and shaft seals. The latter twofactors increase the economic importance of high machine reliability,which is directly dependent on minimizing premature wear andbreakdown of key components.

Balancing, deservedly, has long received attention from machinerymanufacturers and users as a way to minimize vibration and wear.Many shop and field balancing machines, instruments, and methodshave become available over the years. Alignment, which is equallyimportant, has received proportionately less notice than its importancejustifies. Any kind of alignment, even straightedge alignment, is betterthan no alignment at all. Precise, twoindicator alignment is better thanrough alignment, particularly for machines 3600 RPM and higher. Itcan give greatly improved bearing and seal life, lower vibration, andbetter overall reliability. It does take longer, however, especially thefirst time it is done to a particular machine, or when done byinexperienced personnel. The process operators and mechanicalsupervisors must be made aware of this time requirement. If theyinsist on having the job done in a hurry. they should do so with fullknowledge of the likelihood of poor alignment and reduced machinereliability. Figure 51 shows a serious machinery failure which startedwith pipinginduced misalignment, progressed to coupling distress,bearing failure, and finally, total wreck.

Alignment and Balancing

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Prealignment Requirements

The most important requirement is to have someone who knows what heis doing, and cares enough to do it right. Continuity is another importantfactor. Even with good people, frequent movement from location to

location can cause neglect of things such as tooling completeness andprealignment requirements.

The saying that “you can’t make a silk purse out of a sow’s ear” also

applies to machinery alignment. Before undertaking an alignment job, itis prudent to check for other deficiencies which would largely nullify thebenefits or prevent the attainment and retention of good alignment. Hereis a list of such items and questions to ask oneself: Foundation Adequatesize and good condition? A rule of thumb calls for concrete weight equalto three times machine weight for rotating machines, and five times forreciprocating machines. Grout Suitable material, good condition, with novoids remaining beneath baseplate? Tapping with a small hammer candetect hollow spots, which can then be filled by epoxy injection or othermeans. This is a lot of trouble, though, and often is not necessary if the

lack of grout is not causing vibration or alignment drift.

Baseplate Designed for adequate rigidity? Machine mounting pads level,flat, parallel, coplanar, clean? Check with straightedge and feeler gauge.Do this upon receipt of new pumps, to make shop correction possibleand maybe collect the cost from the pump manufacturer. Shims clean, ofadequate thickness, and of corrosion and crushresistant material? Ifcommercial precut shims are used, check for actual versus markedthicknesses to avoid a soft foot condition. Machine holddown bolts of

adequate size, with clearance to permit alignment corrective movement‘?Pad height leaving at least 2 in. jacking clearance beneath center at eachend of machine element to be adjusted for alignment? If jackscrews arerequired, are they mounted with legs sufficiently rigid to avoid deflection?Are they made of type 3 16 stainless steel, or other suitable material, toresist field corrosion? Water or oil cooled or heated pedestals are usuallyunnecessary, but can in some cases be used for onstream alignment

thermal compensation.

Piping Is connecting piping well fitted and supported, and sufficientlyflexible, so that no more than 0.003 in. vertical and horizontal(measured separately not total) movement occurs at the flexiblecoupling when the last pipe flanges are tightened? Selective flangebolt tightening may be required, while watching indicators at thecoupling. If pipe flange angular misalignment exists, a “dutchman” ortapered filler piece may be necessary. To determine filler piecedimensions,

measure flange gap around circumference, then calculate as follows:

Gasket 0. D . I Flange O.D. I = l/8 in. + (Max. Gap Min. Gap) MaximumThickness of Tapered Filler Piece1/8 in. = Dutchman Minimum Thickness(180’ from Maximum Thickness). Dutchman OD and ID same as gasketOD and ID.

Spiral wound gaskets may be helpful, in addition to or instead of atapered filler piece. Excessive parallel offset at the machine flange

connection cannot be cured with a filler piece. It may be possible toabsorb it by offsetting several successive joints slightly, taking advantageof clearance between flange bolts and their holes. If excessive offsetremains, the piping should be bent to achieve better fit. For the“stationary” machine

element, the piping may be connected either before or after thealignment is doneprovided the foregoing precautions are taken, andfinal alignment remains within acceptable tolerances. In some cases,pipe expansion or movement may cause machine movement leadingto misalignment and increased vibration. Better pipe supports orstabilizers may be needed in such situations. At times it may be

necessary to adjust these components with the machine running, thusaligning the machine to get minimum vibration. Sometimes, changingto a more tolerant type of coupling, such as elastomeric, may help.

Coupling Some authorities recommend installation on typical pumpsInstallation and drivers with an interference fit, up to .OW5 in. per in. of

shaft diameter. In our experience, this can give problems insubsequent removal or axial adjustment. If an interference fit is to be

used, we prefer a light onesay .OOO3 in. to .OOO5 in. overall,regardless of diameter. For the majority of machines operating at 3600

RPM and below, you can install couplings with .0005 in. overalldiametral clearance, using a setscrew over the keyway. For hydraulicdilation couplings and other nonpump or special categories, see

manufacturers’ recommendations or appropriate section of this text.Many times, highperformance couplings require interference fits as

high as .0025 in. per in. of shaft diameter.

Coupling cleanliness, and for some types, lubrication, are importantand should be considered. Sending a repaired machine to the field

with its lubricated couplinghalf unprotected, invites lubricantcontamination, rusting, dirt accumulation, and premature failure.

Lubricant should be chosen from among those recommended by thecoupling manufacturer or a reputable oil company. Continuous runningbeyond two years is inadvisable without inspecting a grease lubricatedcoupling, since the centrifuging effects are likely to cause caking andloss of lubricity. Certain lubricants, e.g., Amoco and Koppers couplinggreases, are reported to eliminate this problem, but visual externalinspection is still advisable to detect leakage. Continuous lube

couplings are subject to similar problems, although such remedies asantisludge holes can be used to allow longer runs at higher speeds.By far the best remedy is clean oil, because even small amounts ofwater will promote sludge formation. Spacer length can be important,since parallel misalignment accommodation is directly proportional to

such length.

Alignment Tolerances

Before doing an alignment job, we must have tolerances to worktoward. Otherwise, we will not know when to stop. One type of“tolerance” makes time the determining factor, especially on amachine that is critical to plant operation, perhaps the only one of itskind. The operations superintendent may only be interested in gettingthe machine back on the line,fast. If his influence is sufficient, the jobmay be hurried and done to rather loose alignment tolerances. Thiscan be unfortunate, since it may cause excessive vibration, prematurewear, and early failure. This gets us back to the need for having thetools and knowledge for doing a good alignment job efficiently. Somuch for the propagandanow for the tolerances.

Tolerances must be established before alignment, in order to knowwhen to stop. Various tolerance bases exist. One authorityrecommends ‘hmil maximum centerline offset per in. of couplinglength, for hot running misalignment. A number of manufacturers havegraphs which recommend tolerances based on coupling span andspeed. A common tolerance in terms of faceandrim measurements is.003in. allowable face gap difference and centerline offset. Thisignores the resulting accuracy variation due to face diameter andspacer length differences, but works adequately for many machines.

Be cautious in using alignment tolerances given by couplingmanufacturers. These are sometimes rather liberal and, while perhapstrue for the coupling itself, may be excessive for the coupledmachinery. A better guideline is illustrated in Figure 52, which showsan upper, absolute misalignment limit, and a lower, “don’t exceed forgood longterm operation limit.” The real criterion is the runningvibration. If excessive, particularly at twice running frequency andaxially, further alignment improvement is probably required. Analysisof failed components such as bearings, couplings, and seals can alsoindicate the need for improved alignment.

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Figure 52 can be applied to determine allowable misalignment formachinery equipped with nonlubricated metal disc and diaphragmcouplings, up to perhaps 10,000 rpm. If the machinery is furnished withgeartype couplings, Figure 52 should be used up to 3,600 rpm only. Atspeeds higher than 3,600 rpm, gear couplings will tolerate with impunityonly those shaft misalignments which limit the sliding velocity ofengaging gear teeth to less than perhaps 120 in. per minute. For gearcouplings, this velocity can be approximated by V = (TDN) tancr, where

resimmmmmm Say, for example, we were dealing with a 3560 rpmpump coupled to a motor driven via a 6in. pitch diameter gearcoupling. We observe a total indicator reading of 26 mils in the verticalplane and a total indicator reading of 12 mils in the horizontal plane.The distance between the flexing member of the coupling, i.e., flexingmember on driver and flexing member on driven machine, is 10 in.The total net indicator reading is [(26)2 + (12)?]''* = 28.6 mils. Tan CY

= (1/2)(28.6)/10) = 1.43 milslin., or 0.00143 in./in. The sliding velocityis therefore [(~)(6)(3560) (0.00143)1 = 96 in. per minute. Since this isbelow the maximum allowable sliding velocity of 120 in. per minute,the installation would be within allowable misalignment.

Choosing an Alignment Measurement Setup

Having taken care of the preliminaries, we are now ready to choosean alignment setup, or arrangement of measuring instruments. Manysuch setups are possible, generally falling into three broad categories:faceand rim, reverseindicator, and facefacedistance. The followingsketches show several of the more common setups, numberedarbitrarily for ease of future reference. Note that if measurements aretaken with calipers or ID micrometers, it may be necessary to reversethe sign from that which would apply if dial indicators are used.Figures 53 through 58 show several common arrangements ofindicators, jigs, etc. Other arrangements are also possible. Forexample, Figures 53 and 54 can be done with jigs, either with orwithout breaking the coupling. They can also sometimes be donewhen no spacer is present, by using rightangle indicator extensiontips. Figures 56 and 57 can be set up with both extension arms andindicators on the same side,

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rather than 180" opposite as shown. In such cases, however, a signreversal will occur in the calculations. Also, we can indicate on back offace, as for connected metal disc couplings. Again, a sign reversal willoccur. In choosing the setup to use, personal preference and customwill naturally influence the decision, but here are some basicguidelines to follow.

ReverseIndicator Method

This is the setup we prefer for most alignment work. As illustrated inFigure 59, it has several advantages:

1. Accuracy is not affected by axial movement of shafts in sleevebearings.

2. Both shafts turn together, either coupled or with match marks, socoupling eccentricity and surface irregularities do not reduce accuracyof alignment readings.

3. Face alignment, if desired, can be derived quite easily without direct

measurement.

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4. Rim measurements are easy to calibrate for bracket sag. Face sag, bycontrast, is considerably more complex to measure.

5. Geometric accuracy is usually better with reverseindicator method inprocess plants, where most couplings have spacers.

6. With suitable clampon jigs, the reverseindicator method can be usedquite easily for measuring without disconnecting the coupling orremoving its spacer. This saves time, and for gear couplings, reduces thechance for lubricant contamination.

7. For the more complex alignment situations, where thermal growthand/or multielement trains are involved, reverseindicator can be usedquite readily to draw graphical plots showing alignment conditions andmoves. It is also useful for calculating optimum moves of two or moremachine elements, when physical limits do not allow full correction to bemade by moving a single element.

8. When used with jigs and posts, singleaxis leveling is sufficient for ballbearing machines, and twoaxis leveling will suffice for sleevebearingmachines.

9. For long spans, adjustable clampon jigs are available forreverseindicator application, without requiring coupling spacer removal.Faceandrim jigs for long spans, by contrast, are usually nonadjustablecustom brackets requiring spacer removal to permit face mounting.

10. With the reverseindicator setup, we mount only one indicator perbracket, thus reducing sag as compared to faceandrim, which mountstwo indicators per bracket. (Faceandrim can do it with one per bracket ifwe use two brackets, or if we remount indicators and rotate a secondtime, but this is more trouble.)

There are some limitations of the reverseindicator method. It should notbe used on closecoupled installations, unless jigs can be attachedbehind the couplings to extend the span to 3 in. or more. Failure toobserve this limitation will usually result in calculated moves whichovercorrect for the misalignment.

Both coupled shafts must be rotatable, preferably by hand, andpreferably while coupled together. If only one shaft can be rotated, or ifneither can be rotated, the reverseindicator method cannot be used. Ifthe coupling diameter exceeds available axial measurement span,geometric accuracy will be poorer with reverseindicator than withfaceand rim.

If required span exceeds jig span capability, either get a bigger jig orchange to a different measurement setup such as facefacedistance.Cooling tower drives would be an example of this.

FaceandRim Method

This is the “traditional” setup which is probably the most popular, alAdvantages of faceandrim:

1. It can be used on large, heavy machines whose shafts cannot be

2. It has better geometric accuracy than reverseindicator, for large di

3. It is easier to apply on shortspan and small machines than is rethoughit is losing favor as more people learn about reverseindicator. turned.ameter couplings with short spans.

verseindicator, and will often give better accuracy. Limitations of faceandrim: 1. If used on a machine in which one or both shafts cannot beturned, some runout error may occur, due to shaft or coupling

eccentricity.

If used on a sleeve bearing machine, axial float error may occur. Onemethod of avoiding this is to bump the turned shaft against the axial stopeach time before reading. Another way is to use a second face indicator180" around from the first, and take half the algebraic difference of thetwo face readings after 180" rotation from zero start. Figure 510illustrates this alignment method. Two 2411. tubular graphite jigs areused for light weight and high rigidity. If used with jigs and posts, two orthree axis leveling is required, for ball and sleeve bearing machinesrespectively. Reverseindicator requires leveling in one less axis foreach.

Faceandrim has lower geometric accuracy than reverseindicator, forspans exceeding coupling or jig diameter.

Face sag is often insignificant, but it can occur on some setups, andresult in errors if not accounted for. Calibration for face sag isconsiderably more complex than for rim sag.

For long spans, faceandrim jigs are usually custombuilt bracketsrequiring spacer removal to permit face mounting. Longspan reverseindicator jigs, by contrast, are available in adjustable clampon models notrequiring spacer removal.

Graphing the results of faceandrim measurements is more complexthan with reverseindicator measurements.

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FaceFaceDistance Method

Advantages of facefacedistance:

1. It is usable on long spans, such as cooling tower drives, withoutelaborate longspan brackets or consideration of bracket sag.

2. It is the basis for thermal growth measurement in the Indikon proximityprobe system, and again is unaffected by long axial spans.

3. It is sometimes a convenient method for use with diaphragm couplingssuch as Bendix and Koppers, allowing mounting of indicator holders onspacer tube, with indicator contact points on diaphragm covers.

Limitations of facefacedistance:

1. It has no advantage over the other methods for anything except longspans.

2. It cannot be used for installations where no coupling spacer is present.

3. Its geometric accuracy will normally be lower than either of the othertwo methods.

4. It may or may not be affected by axial shaft movement in sleeve

bearings, but this can be avoided by the same techniques as for faceandrim.

LaserOptic Allgnment

In the early 1980’s, by means of earthbound laser beams and a reflectormounted on the moon, man has determined the distance between earthand the moon to within about 6 inches. Such accuracy is a feature ofoptical measurement systems, as light travels through space in straightlines, and a bundled laser ray with particular precision.

Thus, critical machinery alignment, where accuracy of measurement is ofparamount importance, is an ideal application for a laseroptic alignmentsystem.

The inherent problems of mechanical procedure and sequence ofmeasuring have been solved by Prueftechnik Dieter Busch, of 8045Ismaning (West Germany), whose OPTALIGN@ system comprises asemiconductor laser emitting a beam in the infrared range (wavelength820 mm), along with a beamfinder incorporating an infrared detector. Thelaser beam is refracted through a prism and is caught by areceiver/detector.

These lightweight, nonbulky devices are mounted on the equipmcntshafts, and only a cordconnected microcomputer module is external tothe beam emission and receiverldetector devices. The prism redirectsthe beam and allows measurement of parallel offset in one plane andangularity in another, thus simultaneously controlling both. In one 360"rotation of the shafts all four directional alignment corrections aredetermined.

The receiver is a biaxial analog photoelectric semiconductor positiondetector, yielding mathematical results to within one micron. Data forcomputation are entered automatically through a cable direct from thereceiver/ detector. The only information still to be entered manually is therelative position, 4 times, at 0, 90, 180 and 270".

With the data automatically obtained from the receiver/detector, themicrocomputer instantaneously yields the horizontal and verticaladjustment results for the alignment of the machine to be moved.

Physical contact between measuring points on both shafts is no longerrequired, as this is now bridged by the laser beam, eliminating thepossibilities for error arising from gravitational hardware sag as well as

from sticky dial indicators, etc. The system's basic attachment is stillcarried out with a standard quickfit bracketing system, or with any othersuitable attachment hardware.

If the reader owns an OPTALIGN@ system, he does not have to beconcerned with sag. Other readers must continue the checkout process.

Checking for Bracket Sag

Long spans between coupling halves may cause the dial indicator fixtureto sag measurably because of the weight of the fixture and the dialindicators. Although sag may be minimized by proper bracing, sageffects should still be considered in vertical alignment, To determine sag,install the dial indicators on the alignment fixture in the same orientationand relative position as in the actual alignment procedure with the fixtureresting on a level surface as shown in Figure 51 I. With a small sling andscale, lift the indicator end of the fixture so that the fixture is in thehorizontal position. Note the reading on the scale. Assume for examplethat the scale reading was 7.5 Ibs. Next, mount the alignment fixture onthe coupling hub with the dial indicator plunger touching the top verticalrim of the opposite coupling hub. Set the dial indicator to zero. Next,locate the sling in the same relative position as before and, whileobserving the scale, apply an upward force so as to repeat the previousscale reading (assumed 7.5 Ibs in our example). Note the dial indicatorreading while holding the upward force.

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Let us assume for example that we observe a dial indicator reading of 0.004 in. Using this specific methodology, sag error applies equallyto the top and bottom readings. Therefore, the sag correction to thetotal indicator reading is double the indicated sag and must bealgebraically subtracted from the bottom vertical parallel reading, i.e., (2) ( .004) = + .008 correction to bottom reading. This method is aclever one for facemounted brackets. For clampon brackets,however, it would be easier and more common to attach them to ahorizontal pipe on sawhorses, and roll top to bottom. Figure 512shows this conventional method which, except for the sagcompensator device, is almost universally employed. The sagcompensator feature incorporates a weightbeam scale which appliesan upward force when the indicator bracket is located at the top of themachine shaft, and an equal, but opposite, force when the indicatorbracket and shaft combination is rotated to the down position, 180"removed.

In any event, let us assume that we obtain readings of 0 and + 0.160in. at the top and bottom vertical parallels respectively. We correct forsag in the following manner:

Bracket Sag Effect on Face Measurements

Bracket sag is generally thought to primarily affect rim readings, with

little effect on face readings. Often this is true, but some risk may beincurred by assuming this without a test. Unlike rim sag, face sageffect depends not only on jig or bracket stiffness, but on its geometry.Determining face sag effect is fairly easy. First get rim sag for span tobe used (we are referring here to the full indicator deflection due tosag when the setup is rotated from top to bottom). This may beobtained by trial, with rim indicator only, or from a graph of sagscompiled for the bracket to be used. Then install a setup with rimindicator only, on Calibration pipe or on actual field machine, and “layon” the face indicator and accessories, noting additional rim indicatordeflection when this is done. Double this additional deflection, and addit to the rim sag found previously, if both the face and rim indicatorsare to be used simultaneously. If the face and the rim indicators are tobe used separately, to reduce sag, use the original rim sag in thenormal manner, and use this same original rim sag as shortly to bedescribed in determining face sag effectin this latter case utilizing arim indicator installed temporarily with the face indicator for thispurpose. If the face indicator is a different type (Le., different weight)from the rim indicator, obtain rim sag using this face indicator on therim, and use this figure to determine face sag effect.

Now install face and rim setup on the actual machine, and zero theindicators. With indicators at the top, deflect bracket upward anamount equal to the appropriate rim sag, reading on the rim indicator,and note the face indicator reading. The face sag correction withindicators at bottom would be this amount with opposite sign. Ifzeroing the setup at the bottom, the face sag correction at the topwould be this amount with same sign (if originally determined at top,as described).

Face Sag EffectExamples

Example 1

Face and rim indicators are to be used together as shown in Figure 53. Assume you will obtain the following from your sag test: Rim sagwith rim indicator only = .004 in. Rim sag with two indicators = .007 in.Mount the setup on the machine in the field, and with indicators at top,deflect the bracket upward .007 in. as measured on the rim indicator.When this is done, the face indicator reads plus .002 in. Face sagcorrection at the bottom position would therefore be minus .002 in. Ifyou wish to zero at the bottom for alignment, but otherwise have dataas noted, the face sag correction at the top would be plus .002 in.

Example 2

Face and rim indicators are to be used separately to reduce sag. Bothindicators are the same type and weight. Other basic data are also thesame.

Install face indicator and temporary rim indicator on the machine in thefield, and place in top position. Zero indicators and deflect upward,004 in. as measured on rim indicator. Face indicator reads plus .0013in. Face sag correction at the bottom would therefore be minus .0013in, If zeroing at the bottom for alignment, but otherwise the same asabove, face sag correction at top would be plus .0013 in. Example 3

This will determine sag for “3Indicator FaceandRim Setup” shown inFigure 54.

Set up the jig to the same geometry as for field installation but with rimindicator only and roll 180” top to bottom on pipe to get total singleindicator rim sag (Step 1).

Zero rim indicator on top and add or “lay on” face indicator, noting rimindicator deflection that occurs (Step 2). Double this __ (Step 3).

Add it to original total single indicator rim sag (Step 1). (Step 4). Thisfigure, preceded by a plus sign, will be the sag correction for the rimindicator readings taken at bottom. With field measurement setup asshown, zero all indicators, and deflect the indicator end of the upperbracket upward an amount equal to the total rim sag (Step 4). Notethe face sag effect by reading the face indicator. This amount, withopposite sign, is the face sag correction to apply to the readings takenat the lower position (Step 5). Now deflect the upper bracket backdown from its “total rim sag” deflection an amount equal to Step 3.

The amount of sag remaining on the face indicator, preceded by thesame sign, is the sag correction for the single face indicator beingread at the top position (Step 6).

All of the foregoing refers of course to bracket sag. In long machines,we will also have shaft sag. This is mentioned only in passing, sincethere is no need to do anything about it at this time. Our “pointbypoint” alignment will automatically take care of shaft sag. For initialleveling of large turbogenerators, etc., especially if using precisionoptical equipment, shaft sag must be considered. Manufacturers ofsuch machines know this, and provide their erectors with suitable data

for sag compensation. Further discussion of shaft sag is beyond thescope of this text.

Leveling Curved Surfaces

It is common practice to set up the “rim” dial indicators so theircontact tips rest directly on the surface of coupling rims or shafts. Ifgross misalignment is not present, and if coupling and/or shaftdiameters are large, which is usually the case, accuracy will oftenbe adequate. If, however, major misalignment exists, and/or the rimor shaft diameters are small, a significant error is likely to bepresent. It occurs due to the measurement surface curvature, asillustrated in Figures 513 and 514. This error can usually berecognized by repeated failure of topplusbottom (T + B) readingsto equal sideplusside (S + S) readings within one or twothousandths of an inch, and by calculated corrections resulting inan improvement which undershoots or overshoots and requiresrepeated corrections to achieve desired tolerance. A way tominimize this error is to use jigs, posts, and accessories which“square the circle.” Here we attach flat surfaces or posts to thecurved surfaces, and level

them at top and bottom dead center. This corrects the error as shownin Figure 514.

For this method to be fully effective, rotation should be performed ataccurate 90” quadrants, using inclinometer or bubblevial device. Inmost cases, however, this error is not enough to bother eliminating itis easier just to make a few more corrective moves, reducing the erroreach time.

Jig Posts

The preceding explanation showed a rudimentary auxiliary surface, or“jig post,” used for “squaring the circle.” A more common reason forusing jig posts is to permit measurement without removing the spaceron a concealed hub gear coupling. If jig posts are used, it is importantthat they be used properly. In effect, we must ensure that the surfacescontacted by the indicators meet these criteria:

As already shown, they must be leveled in coordination at top andbottom dead centers, to avoid inclined plane error.

If any axial shaft movement can occur, as with sleeve bearings, thesurfaces should also be made parallel to their shafts. This can bedone by leveling axially at the top, rotating to the bottom, and

rechecking. If bubble is not still level, tilt the surface back toward levelfor a half correction.

If face readings are to be taken on posts, the post face surfacesshould be machined perpendicular to their rim surfaces. In addition tothis, and to steps 1 and 2 just described, rotate shafts so posts arehorizontal. Using a level, adjust face surfaces so they are vertical.Rotate 180” and recheck with level. If not still vertical, tilt back towardvertical to make a half correction on the bubble. This will accomplishour desired objective of getting the face surface perpendicular to theshaft in all measurement planes.

The foregoing assumes use of triaxially adjustable jig posts. If suchposts are not available, it may be possible to get good results usingaccurately machined nonadjustable posts. If readings and correctionsdo not turn out as desired, however, it could pay to make the levelchecks as describedthey might pinpoint the problem and suggest asolution such as using a nonpost measurement setup.

interpretation and Data Recording

Due to sag as well as geometry of the machine installation, it isdifficult and deceptive to try secondguessing the adequacy ofalignment solely from the “raw” indicator readings. It is necessary tocorrect for sag, then note the “interpreted” readings, then plot orcalculate these to see the overall pictureincluding equivalent facemisalignment if primary readings were reverseindicator on rims only.Sometimes thermal offsets must be included, which furthercomplicates the overall picture. As a way to systematically considerthese factors and arrive at a solution, it is helpful to use prepared dataforms and stepwise calculation. Suppose we are using the twoindicator facerim method shown in Figure 53; let’s call it “Setup #1.”To start, prepare a data sheet as shown in Figure 515. Next, measureand fill in the “basic dimensions’’ at the top. Then, fill in the orientationdirection, which is north in our example. Next, take a series ofreadings, zeroing at the top, and returning for final readings whichshould also be zero or nearly so. Now do a further check: Add the topand bottom readings algebraically (T + B), and add the side readings(S + S). The two sums should be equal, or nearly so. If the checks arepoor, takc a new set of readings. Do the checks before accounting forbracket sag. Now, fill in the known or assumed bracket sag. If thebracket does not sag (optimist!), fill in zero. Combine the sagalgebraically with the vertical rim reading as shown, and get the netreading using (+) or () as appropriate to accomplish the sag

correction. A wellprepared form will have this sign printed on it. If itdoes not, mentally figure out what must be done to “unsag” thebracket in the final position, and what sign would apply when doing so.

Now we are ready to interpret our data in the space provided on theform. To do this, first take half of our net rim reading:

Formullll

This is because we are looking for centerline rather than rim offset.Since its sign is minus, we can see from the indicator arrangementsketch that the machine element to be adjusted is higher than thestationary element, at the plane of measurement. This assumes theuse of a conventional American dial indicator, in which a positivereading indicates contact point movement into the indicator.

By the same reasoning, we can see that the bottom face distanceis .007 in. wider than the top face distance. Going now to thehorizontal readings, we make the north rim reading zero by adding .007 in. to it. To preserve the equality of our algebra,

we also add .007 in. to the south rim reading, giving us .029 in.Taking half of this, we find that the machine element to be adjustedis .0145 in. north of the stationary element at the plane ofmeasurement. Finally, we do a similar operation on our horizontalface readings, and determine that the north face distance is widerby .014 in. The remaining part of the form provides space to put thecalculated corrective

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Nelson’s method is easy to understand, and it works. It is basicallya fourstep procedure in this order:

1. Vertical angular Correction.

2. Vertical parallel correction.

3. Horizontal angular correction.

4. Horizontal parallel correction.

It has three disadvantages, however.

First, it requires four steps, whereas the more complexmathematical methods can combine angular and parallel data,resulting in a twostep correction. Secondly, it is quite likely thatinitial angular correction will subsequently have to be partially “undone,” when making the corresponding parallel correction. Nobodylikes to cut and install shims, then end up removing half of them.Finally, it is designed only for faceandrim setups, and does notapply to the increasingly popular reverseindicator technique.

We will now show two additional examples, wherein the angularand parallel correction are calculated at the same time, for anoverall twostep correction. Frankly, we ourselves no longer usethese methods, nor do we still use Nelson’s method, but are

including them here for the sake of completeness. Graphicalmethods, as shown later, are easier and faster. In particular, thealignment plotting board should be judged extremely useful.Readers who are not interested in the mathematical method maywish to skip to page 192, where the much easier graphical methodsare explained. But, in any event, here is the full mathematicaltreatment.

In our first example, we will reuse the data already given in oursetup No. 1 data sheet.

First, we will solve for vertical corrections:

Using Nelson’s method, we found it necessary to make a 0.053 in.shim correction. Let us arbitrarily say this will be a shim additionbeneath the inboard feet. At the coupling face, we then get a riseof:

[http://4.bp.blogspot.com/_s7mH8WpXY8/SMm4lbfb0PI/AAAAAAAAAT4/HgoTN5Jzzm8/s1600h/17bal16.jpg]

[http://2.bp.blogspot.com/_s7mH8WpXY8/SMm4xyibesI/AAAAAAAAAUA/IPNXJNxXW_I/s1600h/18bal17.jpg]

[http://1.bp.blogspot.com/_s7mH8WpXY8/SMm4380e11I/AAAAAAAAAUI/5i2E8V7Yniw/s1600h/19bal18.jpg]

As you can see, the values found this way are close to those foundearlier. The main problem people have with applying theseformulas is choosing between plus and minus for the terms. Theeasiest way, in our opinion, is to visualize the “as found” conditions,and this will point the way that movement must proceed to go to

zero misalignment. For example, our bottom face distance is widetherefore we need to lower the feet (pivoting at plane A) which wedenote with a minus sign. The machine element to be adjusted ishigher at plane Aso we need to lower it some more, which takesanother minus sign. For the horizontal, our north face distance iswider, so we need to move the feet north (again pivoting at planeA). The machine element to be adjusted is north at plane A, so weneed to move it south. Call north plus or minus, so long as you callsouth the opposite sign. Not really hard, but a lot of people havetrouble with the concept, which is why we prefer to concentrate ongraphical methods , where direction of movement becomes moreobvious. We will get into this shortly, but first let’s do a reverseindicator problem mathematically.

[http://4.bp.blogspot.com/_s7mH8WpXY8/SMm5G36lxiI/AAAAAAAAAUQ/S3eIJVvRLVM/s1600h/20bal19.jpg]

[http://3.bp.blogspot.com/_s7mH8WpXY8/SMm5M3vMoqI/AAAAAAAAAUY/mrG6rnCPmwM/s1600h/21bal20.jpg]

[http://1.bp.blogspot.com/_s7mH8WpXY8/SMm5XaeAciI/AAAAAAAAAUg/pBYtQK0T_iM/s1600h/22bal21.jpg]

[http://1.bp.blogspot.com/_s7mH8WpXY8/SMm5pYZsAwI/AAAAAAAAAUo/3she1coVqhk/s1600h/23bal22.jpg]

[http://2.bp.blogspot.com/_s7mH8WpXY8/SMm5AJSJFI/AAAAAAAAAUw/HgRLdYPP8UE/s1600h/24.bmp]

For our reverseindicator example, we will use the setup shownearlier as Figure 56. Also, we must now refer to the appropriatedata sheet, Figure 518. Finally, we resort to some triangles,

Figures 519 and 520, to assist us in visualizing the situation.

Teknişk Resimmm

Graphical Techniques

Now let’s see how we can do the same thing more easily. To dothis, we will turn to graphical techniques. Reference 7 shows oneversion of this in an article on alignment of barreltype centrifugalcompressors. Its author stretches a stripchart out on a draftingtable, and rules in the machine element shafts, to scale, oriented asshown by reverseindicator readings, much as we did in ourprevious example. Movements to achieve zero offset, or tocompensate for thermal growth, can then be plotted on the samesheet. This technique has the advantage of giving a complete andpermanent written visual record of what is happening, and isespecially useful on multielement machinery

After reworking our first example with the alignment plotting board,we will proceed to our second example, using the reverseindicatorsetup (setup 4). This is illustrated for us in Figures 518 and 524.We will then go on and give workedout examples using the othersetups in Figures 525 through 533.

ThreeIndicator FaceandRim

Figure 527 depicts a pump with ball bearings driven by a motorhaving sleeve bearings. External obstructions prevent the use ofsetups 4 or 5, and the coupling surfaces have considerable runout,making setup 1 inadvisable. It is therefore decided to use setup 2the threeindicator faceandrim. A sag check shows 0.002 in. sagfor the rim indicator bracket. Sag for the face indicators will beignored. A preliminary straightedge alignment is made in thehorizontal plane. Both shafts are then turned together and a set ofvertical readings taken as shown on the accompanying data sheetin Figure 528.

[http://1.bp.blogspot.com/_s7mH8WpXY8/SMm6Fnrni7I/AAAAAAAAAU4/wirozrp2860/s1600h/25bal29.jpg]

[http://4.bp.blogspot.com/_s7mH8WpXY8/SMm_Ew6paWI/AAAAAAAAAVA/NNnJcXJ18mk/s1600h/26bal30.jpg]

[http://3.bp.blogspot.com/_s7mH8WpXY8/SMm_dAGjWLI/AAAAAAAAAVI/ceMH5cbNzQI/s1600h/27bal31.jpg]

[http://3.bp.blogspot.com/_s7mH8WpXY8/SMm_l21YqBI/AAAAAAAAAVQ/AhsHB1gcug0/s1600h/28bal34.jpg]

trains such as the article discusses.

Another graphical technique, which we prefer for most situations, isthe Alignment Plotting Board. It is fast, easy, and accurate, particularlyon the simple twoelement trains comprising the majority of allmachines. It can be used on multielement trains, but is less efficientthan graph paper beyond two elements. To our knowledge, the plottingboard is the only method which handles both the faceandrim andreverseindicator setups with equal ease and can convert from RI toF&R. An additional advantage is its portabilityit is only 8V2 X 11 in.and is made from an “indestructible” polycarbonate plastic. Figure 522 shows it in use.

Let’s return to our first example. For convenience, we will refer to thedata sheet in Figure 515, then show how to find the corrections onthe plotting board. This is graphically explained in Figure 523. Byflipping back and forth between data sheet and plotting boardsketches, you can see where the answers come from. It will help toalso read the instructions that come with the plotting board, if youhave one. With practice, the answers will appear in a minute or two. movements. Although these have been filled in for our example, let’sleave them for the time being, since we are not yet ready to explainthe calculation procedure. We will show you how to get these numberslater. If you think you already know how, go ahead and trythe resultsmay be interesting.

You have now seen the general idea about data recording andinterpretation. By doing it systematically, on a prepared form

corresponding to the actual field setup, you can minimize errors. If youare interrupted, you will not have to wonder what those numbersmeant that you wrote down on the back of an envelope an hour ago.We will defer consideration of the remaining setups, until we haveexplained how to calculate alignment corrective movements. We willthen take numerical examples for all the setups illustrated, and gothrough them all the way. Calculating the Corrective Movements

Many machinists make alignment corrective movements by trial anderror. A conscientious person can easily spend two days aligning amachine this way, but by knowing how to calculate the corrections, thetime can be cut to two hours or less.

Several methods, both manual and electronic, exist for doing suchcalculations. All, of course, are based on geometry, and some arerather complicated and difficult to follow. For those interested in suchthings, see Refercnces 1 through 15. Also, the alignment specialistshould be aware of programmable calculator solutions. These makeuse of popular calculators such as the TI 59 and HP 67. By recordingthe alignment measurements on a prepared form, and entering thesefigures in the prescribed manner into the calculator, the requiredmoves come out as answers. A variation of this is the TRS 80 pocketcomputer which has been programmed to do alignment calculationsvia successive instructions to the user telling him what information toenter.

By far the simplest calculator is the one described earlier inconjunction with the laserbased OPTALIGN@ system. Next to it, werank the IMS calculator. l4 This is designed specifically “from theground up’’ for the more common faceandrim and reverseindicatorcalculations, rather than being a standard commercial calculator orcomputer adapted for alignment. For the more complex multielementtrains, larger central computers can be used directly with telephonelinkups. Ray Dodd’s book (Total Alignment, Reference 3) describesone such system. Another that we saw demonstrated provides notonly the numerical data, but a diagrammatic representation of themachines and their alignment relationship, on a cathode ray tube.

The foregoing electronic systems are popular, and have advantages inspeed, accuracy, and ease of use. They have disadvantages in cost,usability under adverse field and hazardous area conditions, pilferage,sensitivity to damage from temperature extremes and rough handling,and availability to the field machinist at 2:OO A.M. on a holidayweekend. 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 therelationship 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 willbe faster). They have the disadvantage, some say, of requiring morethinking than the programmed electronic solutions, particularly tochoose the plus and minus signs correctly.

The graphical methods, which we prefer, have the advantage of aidingvisualization and avoiding confusion. Their accuracy will sometimesbe lcss than that of the “pure” mathematical methods, but usually notenough to matter. Investment is lowgraph paper and plotting boardsare inexpensive. Speed is high once proficiency is attained, whichusually does not take long.

In this text, we will emphasize the graphical approach. Before doingso, let’s highlight some common manual mathematical calculations.Nelson” published an explanation of one rather simple method anumber of years ago. A shortened explanation is given in Figure 516.For our given example, this would work out as follows:

[http://4.bp.blogspot.com/_s7mH8WpXY8/SMm4Mz9RIBI/AAAAAAAAATg/j3TwSHXDSI/s1600h/14bal13.jpg]

[http://2.bp.blogspot.com/_s7mH8WpXY8/SMm3wJyGlkI/AAAAAAAAATI/78N45mzZNYY/s1600h/11bal10.jpg]

[http://2.bp.blogspot.com/_s7mH8WpXY8/SMm30yxD8EI/AAAAAAAAATQ/PgtHLdJBwPE/s1600h/12bal11.jpg]

Posted 10th September 2008 by Amr Zoair

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5 View comments

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