Allignment Basics

Prepared By

TAUFEEQ ARSHAD

Contents

Introduction/Definition

Types of Alignment

Alignment States

Pre Alignment Checks

Alignment Methods

Thermal Growth

Centering

Reciprocating Machines Alignment

Alignment of V Belts, Pulleys, Sprocket & Gears.

Effects of Misalignment.

Case Histories

Introduction

To bring the rotating members of driver and driven machines in the desired line.

Example

In case of shafts, bringing the two shafts in a straight line / desired line.

In case of pulleys, bringing the neutral axis or the faces of two pulleys in a straight line.

In case of gears, achieving the rolling contact between the gears.

In case of sprockets, bringing the faces in a straight line.

Types of Alignment

In case of shafts, there are two types of alignment.

Radial Alignment

Radial alignment means to check the relative position of

rotating members in the vertical and horizontal planes.

In other words, it must be checked that the axis of

rotation of the members are in line / desired line.

Radial alignment can be further classified as

Radial Vertical alignment

Radial Horizontal alignment

Types of Alignment (Cont.)

Axial Alignment

Axial alignment means to check the relative position

between the axis perpendicular to the axis of rotation of

the two members to be coupled. In other words, it must

be checked that the said axis are parallel or have the

required divergence.

Axial alignment can also be classified as

Axial Vertical alignment

Axial Horizontal alignment

Alignment States

Cold Alignment

Alignment which is carried out when the machine is at cold

state.

Hot Alignment

Alignment which is carried out when the machine is at hot

state.

In Situ Alignment

Alignment which is carried out when the machine is in

operation.

Pre Alignment Checks

Before undertaking an alignment job, it is

prudent to check for other deficiencies which

would largely nullify the benefits or prevent the

attainment and retention of good alignment.

Below is the List of factors to be considered

before checking the alignment:

Pre Alignment Checks (Contd.)

Foundation Adequate size and good condition. A rule of thumb

calls for concrete weight equal to three times machine weight for rotating machines and five times for reciprocating machines.

Grout Suitable material, good condition, with no voids

remaining beneath baseplate. Tapping with a small hammer can detect hollow spots, which can then be filled by epoxy injection or other means.


Baseplate Designed for adequate rigidity. Machine mounting pads

should be flat, parallel and clean. Shims should be made from corrosion and crush-resistant material. If commercial pre-cut shims are used, check for actual versus marked thickness to avoid a soft foot condition. Machine hold-down bolts should be of adequate size, with clearance to permit alignment corrective movement. Pad height should have at least 2 in. jacking clearance beneath center at each end of machine element to be adjusted for alignment. If jackscrews are required, they are to be mounted with legs sufficiently rigid to avoid deflection. Water or oil cooled or heated pedestals are usually unnecessary, but can in some cases be used for onstream alignment thermal compensation.


Piping Check the associated piping is well fitted and supported,

and sufficiently flexible, so that no more than 0.003 in. vertical and horizontal (measured separately not total) movement occurs at the flexible coupling when the last pipe flanges are tightened.

Coupling Installation Some authorities recommend installation on typical pumps

and drivers with an interference fit, up to .0005 in. per in. of shaft diameter. This can give problems in subsequent removal or axial adjustment. If an interference fit is to be used, we prefer a light one-say 0.0003 in. to 0.0005 in. overall, regardless of diameter. Coupling cleanliness, and for some types, lubrication, are important and should be considered.

Line Diagram

Position of the shaft, when the machine is

in cold state, can be represented

graphically. This is called line diagram of

the machine.

It is a very useful tool for visualizing the

actual position of the shaft, when carrying

out the alignment.

Line Diagram

A typical line diagram of Air Compressor (K-

421) is shown bellow.

Turbine HP

Casing LP

Casing

Alignment Methods (Shafts)

There are three methods of aligning the centerline of two

shafts:

Aligning the shafts using feeler gauge & knife edge.

Aligning the shafts with reverse method. It is also

sometimes referred as graphical method.

Aligning the shafts using with dial indicators.

Alignment Methods (Cont.)

Alignment with feeler gauge and knife edge.

Allowed only on flexible coupling, as precise alignment

can not be achieved.

Radial misalignment is checked / corrected with the

help of straight edge or knife edge.

Axial misalignment is checked / corrected with the help

of feeler gauge.

This method is used only for aligning the shafts of non

critical machines.

On critical machines, this method is used only when

enough space is not available on the rotating members

for clamping the alignment fixtures.

Alignment Methods

Graphical or Reverse method

In this method, as the name suggests, graphical

techniques are used for aligning the rotating members.

One set of readings is taken from the loose machine to

the fixed machine, and the second set of readings is

taken from the fixed machine to the loose machine. It is

therefore sometimes referred as reverse method.

Alignment Methods


These readings are then plotted on the graph using

suitable scale. How much the rotating members are

misaligned, can then be calculated from the graph.

In case of pump and motor, usually electric motor is

considered as the loose machine and the pump is

considered as the fixed machine.

Alignment Methods


Fix the clamping fixture on the motors shaft and place

the dial indicator on the coupling hub of the pump. Take

readings and record these values (a, b, c & d) on the

cross.

Then fix the clamping fixture on the pump's shaft and

put the dial indicator on the coupling hub of the motor.

Again take the set of readings and record these values

(e, f, g & h) on the cross.


c - a

2

e - g

2 and B = A =

Plot the two calculated values (A & B) on the graph paper, using appropriate scale, if

required.

Considering plus and minus signs, plot plus value above the required line and

minus value below the required line.


Calculate the misalignment in the elevation with the help of following formula:


Motor (Loose M/C) Pump (Fixed M/C)

Desired Line

A B

Note :

Motor and pump lines to be drawn as per suitable scale



Draw a line through these two points and

determine the thickness of the shims required

at point C and D. Remember to take the scale

(if used) into account.

Remove shims if the value is plus.

Add shims if the value is minus.


Actions required :

Remove shims of thickness x from motor rear feet

Remove Shims of thickness y from motor front feet


Value measured

Desired Line

A D C B

x y


d - b

2

f - h

2 and B = A =

Similarly misalignment in the plan can be calculated

with the help of following formulae :

While noting down the measured values ,i.e. b, d, f & h,

also note down the description of these points as

follows:

b & f = Tool room side

d & h = Elect. Shop side




Plot the two calculated values (A & B) on the

graph paper, using appropriate scale, if required.

Considering plus and minus signs, plot plus value

above the required line and minus value below

the required line.

Move motor feet towards Elect. shop if the value

is plus.

Move motor feet towards tool room if the value is

minus.



Value measured Desired Line

A D C B

x

y

Actions required :

Move motor rear side towards Elect. Shop by x

Move motor front side towards Elect. Shop by y

Reverse Method

Following are the advantages of this method:

Accuracy is not affected by axial movement of shafts in sleeve bearings.

Both shafts turn together, either coupled or with match marks, so coupling eccentricity and surface

irregularities do not reduce accuracy of alignment

readings.

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

Reverse Method (Contd.)

Rim measurements are easy to calibrate for bracket sag.

Geometric accuracy is usually better with reverse method in process plants, where most couplings

have spacers.

With suitable clamp-on jigs, the reverse-indicator method can be used quite easily for measuring

without disconnecting the coupling or removing its

spacer. This saves time, and for gear couplings,

reduces the chance for lubricant contamination.


For more complex alignment situations, where thermal growth and / or multi-element trains are

involved, reverse method can be used quite readily

to draw graphical plots showing alignment conditions

and moves. It is also useful for calculating optimum

moves of two or more machine elements, when

physical limits do not allow full correction to be made

by moving a single element.

When used with jigs and posts, single-axis leveling is sufficient for ball-bearing machines, and two-axis

leveling for sleeve-bearing machines.


For long spans, adjustable clamp-on jigs are available for reverse-indicator application,

without requiring coupling spacer removal.

With the reverse-indicator setup, we mount only one indicator per bracket, thus reducing

sag as compared to face-and-rim, which

mounts two indicators per bracket.


Disadvantages of this method are:

Both coupled shafts must be rotatable, preferably by hand, and preferably while

coupled together.

If the coupling diameter exceeds available axial measurement span, geometric accuracy

will be poorer with reverse method.


Alignment with dial indicators.

For using dial indicators, it is necessary to

prepare a suitable outfit, which can hold three dial

indicators simultaneously. One dial indicators (R),

with the axis in the radial direction, will measure

the radial misalignment of the shafts. The two dial

indicators (A1 and A2), with the axis in the axial

direction, will measure the axial misalignment of

the shafts.


Note :

For having accurate readings, ensure dial indicator rod

remains perpendicular to the face while taking readings.


Alignment with dial indicators

Alignment data can be measured

By rotating one of the shafts, allowing the dial indicator slide

on the flange of the other shaft which remains fixed.

By rotating both the shafts at the same time.

If possible, proceed in the later manner because in this case

the collected alignment data will be independent of the

machining and shape of the coupling flanges.


Dial Indicator

Dial Indicator works with the index of mm scale. Before rotating the shaft and collecting the

misalignment data, ensure that all the three dial

indicators are set to zero. Also make sure that

traveling margin is available in these indicators.

When recording the data, the plus sign shall be given when the rod of the dial indicator goes back into its

seat or move inward. Minus sign shall be given when

the rod comes out.

When the dial indicator main pointer rotates by 3600,

the dial indicator small pointer will show 1mm

displacement of the rod


Radial Alignment Place the dial indicator on the rim of the

coupling hub and secure it with the help of suitable outfit.

Measure the data during a rotation of 3600. The algebraic sum of the values read on the horizontal plane (900 & 2700) will be equal to the values read on the vertical plane (00 and 1800).

When noting down the alignment values, always specify the hub (Driver or Driven) on which the dial indicator moves.


Radial vertical misalignment = x

2

Radial Alignment (Vertical Plane)

Dial Indicator readings:

-y -y = -x

- y

- x

- y

0

Place shims of thickness x/2 mm under all the feet of machine B

Action required :

A B

A

B

Side View


Radial Vertical Misalignment = x

2

Radial Alignment (Vertical Plane)

(-y -y = +x)


- y

+x

- y

0

Remove shims of thickness x/2 mm from all the feet of machine B

Action required :

B A

B A

Side View


Radial Alignment (Horizontal Plane)

x

2 Radial Horizontal Misalignment =


(x -x = 0)

+x

0

-x

0 B A

B

A

Plan View

Move the motor (A) upward by distance x/2. During movement,

ensure that axial alignment may not get disturbed.

Action required :


Axial Alignment Place the two dial indicators at 1800 by the

vertical axis.

The necessity to use two dial indicators is due to the fact that axial displacement of the two shafts to be coupled may occur during the rotation of the two flanges.

By the use of two dial indicators the possible displacements along the axis are annulled, where the face displacements of the two hubs to be coupled remain unattended.


Axial Alignment (Vertical Plane)

Measure the data during a complete rotation of 3600.

The value of axial misalignment on the vertical plan will be the algebraic half difference of the reading (consider

with their signs) made on the dial indicators A1 and A2

after a rotation of 1800 i.e.

A1 a = 0

d

c

b

A2 e

h

g = 0

f

c - e

2 Axial vertical Misalignment =



A2 +e

h

g = 0

f

A1 a = 0

d

-c

b

Dial Indicators readings:

Case 01

Side view

A1= 0

A2 = +e

A1= -c

A2 = 0

A1

A2

c - e

2 Axial vertical misalignment =

Whenever misalignment result has minus

sign, the flanges are open downwards.


Axial Alignment (Vertical Plane) Case 02

A1= 0

A2 = 0

A1= 0

A2 = 0

A1

A2

Side View

A1 a = 0

d

c = 0

b

A2 e = 0

h

g = 0

f


c - e


Whenever misalignment result is 0, there is no axial misalignment in vertical plane.



A1 a = 0

d

+c

b

A2 -e

h

g = 0

f


Case 03

Side view

A1= 0

A2 = -e

A1= +c

A2 = 0

A1

A2

c - e


Whenever misalignment result has plus

sign, the flanges are open upwards.


Axial Alignment (Horizontal Plane)

Measure the data during a complete rotation of 3600.

The value of axial misalignment on the horizontal plan will be the algebraic half difference of the reading (considered with their signs) made on the dial indicators A1 and A2 after a rotation of 900

and 2700 c.e.

Axial Horizontal Misalignment =

A1 a = 0

d

c

b

A2 e

h

g = 0

f

(b d) (h - f)

2



A1 a = 0

+d

c

-b

A2 e

+h

g = 0

-f


Axial horizontal misalignment = (b - d) - (h - f)

2

Whenever misalignment result has minus

sign, the flanges are open to the left.

Case 01

Right

Left

A1

A2

Plan view

A1 = + d

A2 = + h

A1 = - b

A2 = - f



A1 a = 0

-d

c

+b

A2 e

-h

g = 0

+f


Axial horizontal misalignment = (b d) (h - f)

2

Case 02

A1= - d

A2 = -h

A1= +b

A2 = + f

A1

A2

Left

Right

Plan view Whenever misalignment result has plus

sign, the flanges are open to the right.



A1 a = 0

d

c

b

A2 e

h

g = 0

f


Case 03

Plan view

A1 = d

A2 = h

A1 = b

A2 = f

A1

A2

Left

Right

Axial horizontal misalignment = (b d) (h - f)

2

= 0

Misalignment result is o, the flanges are axially aligned in horizontal plane.


Alignment Correction Procedure

After taking the complete alignment data, draw

the line diagram. This helps in visualizing the

actual physical condition of the machine. It thus

helps in deciding the actions to be taken in

order to get the desired alignment readings.

Always correct the axial alignment in the

vertical plane first. One performs the correction

by changing the height of the shims placed

underneath the feet of the machine.


g = 0

e

h f b d

c

a = 0

A1 A2

Axial Misalignment in the Vertical plane


Thickness of the shim to be removed from the rear feet, in order to align

the shafts, can be obtained from the formula

Where (Consider the sign)

S = X . L

X= C - E

2

L = Distance b/w the feet.

= Distance b/w two dial indicators.

If the correction to be made is noticeable, it is recommended to adjust

the shim placed between the grouted plates and the bedplates.

Axial Misalignment in the Vertical plane


Alignment Correction Procedure

After correcting the axial alignment in the vertical plane, correct the radial alignment in the vertical plane. Raise

or Lower the machine by adding or removing the shims

from all the feet of the machine. By doing such, axial

alignment of the machine in both the planes would not

change.

Best method to carry out the above action is to tight the bolts of both the feet of one side first and than add /

remove the shims from the feet of another side. Repeat

the same process for removing / adding the shims from

the feet of first side.


Alignment Correction Procedure After correcting the axial and radial alignment

in the vertical plane, correct the axial alignment in the horizontal plane.

As per alignment readings, make any foot of the machine a pivot. This can be done by tightening the bolt of that particular machine foot. After that, move the machine in a horizontal plane about the pivot to get the desired alignment readings.

In the last, correct the radial alignment in the horizontal plane.


Axial Misalignment in the Horizontal Plan

(Viewing from the Top)

Foot to be pivoted

Face & Rim Method

Following are the advantages of this method:

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

It has better geometric accuracy than reverse-indicator, for large diameter couplings with

short spans.

It is easier to apply on short-span and small machines.

Face & Rim Method (Contd.)

Disadvantages of this method are:

If used on a machine in which one or both shafts cannot be turned, some runout error may occur, due to shaft or coupling eccentricity.

If used on a sleeve bearing machine, axial float error may occur. One method of avoiding this is to bump the turned shaft against the axial stop each time before reading. Another way is to use a second face indicator 180 around from the first.

If used with jigs and posts, two or three axis leveling is required, for ball and sleeve bearing machines respectively.

Face & Rim Method (Contd.)

Face-and-rim has lower geometric accuracy than reverse-indicator, for spans exceeding coupling or jig diameter.

Face sag is often insignificant, but it can occur on some setups, and result in errors if not accounted for. Calibration for face sag is considerably complex.

For long spans, face-and-rim jigs are usually custom-built brackets requiring spacer removal to permit face mounting.

Graphing the results of face-and-rim measurements is more complex than with reverse-indicator measurements.

Leveling Curved Surfaces

It is common practice to set up the rim dial indicators so their contact tips rest directly on the surface of coupling rims or shafts. If gross misalignment is not present, and if coupling and/or shaft diameters are large, which is usually the case, accuracy will often be adequate.

If, however, major misalignment exists, and/or rim or shaft diameters are small, a significant error is likely to be present. It occurs due to the measurement surface curvature.

This error can usually be recognized by repeated failure of top-plus-bottom (T+B) readings to equal side-plus-side (S+S).

Jig Posts

Jig post is a rudimentary auxiliary surface, used for squaring the circle. Another reason for using jig posts is to permit measurement without removing the spacer on a concealed hub gear coupling. If jig posts are used, it is important that they be used properly. In effect, we must ensure that the surfaces contacted by the indicators meet these criteria:

They must be leveled in coordination at top and bottom dead centers, to avoid inclined plane error.

Jig Posts If any axial shaft movement can occur, as with sleeve

bearings, the surfaces should also be made parallel to their

shafts. This can be done by leveling axially at the top, rotating

to the bottom, and rechecking. If bubble is not still level, tilt the

surface back toward level for a half correction.

If face readings are to be taken on posts, the post face surfaces should be machined perpendicular to their rim

surfaces. In addition to this, and to previous steps just

described, rotate shafts so posts are horizontal. Using a level,

adjust face surfaces so they are vertical. Rotate 180o and

recheck with level. If not still vertical, tilt back toward vertical to

make a half correction on the bubble. This will accomplish our

desired objective of getting the face surface perpendicular to

the shaft in all measurement planes.

Thermal Growth

Thermal growth of machines may or may not be significant for alignment purposes.

In addition, movement due to pipe effects, hydraulic forces and torque reactions may enter the picture.

Vibration, as measured by seismic or proximity probe instrumentation, can give an indication of whether

thermal growth is causing misalignment problems

due to differences between ambient and operating

temperatures.

Thermal Growth (contd.)

If no problem exists, then a zero-zero ambient alignment should be sufficient. Through experience it has been learnt that such zero-zero alignment is adequate for majority of electric motor driven pumps.

Zero-zero has the further advantage of simplicity, and of being the best starting point when direction of growth is unknown.

For these reasons, zero-zero is preferable unless we have other data that appear more trustworthy, or un-less we are truly dealing with a predictable hot pump thermal expansion situation.

Thermal Growth (Contd.)

If due to vibration or other reasons it is decided that thermal growth correction should be applied, several

approaches are available, as follows:

Pure guesswork, or guesswork based on experience.

Trial-and-error.

Manufacturers recommendations.

Calculations based on measured or assumed metal

temperatures, machine dimensions, and handbook

coefficient of thermal expansion.


Calculations based on rules-of-thumb, which incorporate the basic data of previous approach.

Shut down, break the coupling, and measure before machine gets cool down.

Same as the previous approach, except use clamp-on jigs to get faster measurements without having to break the coupling.

Make mechanical measurements of machine housing growth during operation, referenced to base plate or foundation, or between machine elements.


Measure the growth using precise optical instrumentation.

Make machine and / or piping adjustments while running, using vibration as the primary reference.

Laser measurement represents another possibility.

Same as the previous approach, except use eddy current shaft proximity probes as the measuring elements, with electronic indication and / or recording.

Centering

(Machine Internal Alignment)

Centering refers to the alignment of the machine

internals. It is carried out with the help of dummy

shaft. Dummy shaft has adjustable legs. With the

help of dummy shaft and two dial indicators,

which run on extreme casing ends (Machine front

& exhaust sealing areas), casing central axis is

achieved. Length of the adjustable legs is then

locked. Dummy shaft is then removed and all the

machine internals are installed. All these internals

are then aligned with the help of dummy shaft.

Centering

Centering can be classified into two types.

Internal Centering

Centering of the machine internals, carried out when the

machine is in dismantled form is called internal

centering.

External Centering

External Centering refers to the checking of machine

rotor center when the machine is in assembled form.

Reciprocating M/cs Alignment

Perform the following operations in order to align and to couple the machine which then

form the unit.

Install the flywheel in the compressor shaft end.

Record the shaft deflections as follows. Put on inside micrometer in the crank nearest the

driver as shown in figure.

Slowly rotate the shaft and read the shaft deflection in a complete turn.


Detect the mean oscillation of the flywheel during a

complete revolution of the compressor shaft and stop

the shaft at this point.

The new centre line assumed by the compressor

shaft due to flywheel weight will be the reference

centre line for the subsequent alignment.

Align the slow shaft of the speed reduce to the

compressor shaft in this position, then align the

speedy shaft of the speed reduce to the driver.


Tighten the bolts which lock the speed reducer and

the driver to the bedplate.

Couple the compressor shaft and check again the

compressor shaft deflection which shall be the

same those read before the coupling.

Important Tips

If the machine has more than four feet, then it is better to carry out the alignment of the machine

by reverse / graphical method.

Always carry out the alignment job in the early day time. This will help in precluding the error

which can occur due to sunlight.

Shims should be kink free. Also try to keep the no. of shim as less as possible.

Before alignment, always ensure that there is no soft footing in the machine. If it exists, remove it prior to align.

Important Tips

Do not expect symmetrical thermal growth in unsymmetrical machines.

Before decoupling the machine, take alignment reading, if time permits. It serves as a reference

reading, as some time it becomes difficult to get

the desired readings.

Associated piping / supports have a tendency to induce stresses in the machine during operation if

they are not properly designed. If machine gets

misaligned during operation, review the same

Gear Alignment

Gear is a very costly element of the

machine. If the two gears are not fitted and

aligned properly, they will definitely get

worm out rapidly. Moreover in the aftermath

of gear failure, major machine damage can

also be happened.

It is therefore imperative to take extra care

while fitting any gear.

Gear Alignment

Following are the ways of checking the alignment

of the gears.

Check the tooth flank contact pattern by applying prussian blue, using a piece of felt.

Place two lead wire on the marked tooth (One on the left and the other on the right) of the pinion.

Rotate the gear so that the wires are flattened.

Measure the thickness of the wires. The

maximum variation in flank clearance measure

not exceed 0.02mm.

Gear Alignment

Pulley & Sprocket Alignment

V Belt pulleys or sprockets can be aligned

with straight edge bars or with strings. Both

axial and redial misalignments can be

corrected.

Sprockets Alignment

Pulleys Alignment

Effects of Misalignment

Misalignment can cause the following problems

on the running machine.

Vibration occurs due to misalignment in the machine and associated / linked equipments.

Excessive wear and temperature rise in the bearings.

It causes coupling failure.

Abnormal noise arises because of misalignment

Over loading of prime movers

Decreases the efficiency of the machine

Thank You

Reciprocating Machine Train Alignment

Documents

Allignment Basics