Shaft Alignment

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Alignment

Accurate alignment is vital to the operating life of rotating equipment. Bearings, mechanical seals, packing, and couplings a directly affected by the alignment of shaft center lines. The goal of the alignment process is to create a straight line through t coupling, as shown in Figure 1. The two coupled shafts are considered to be perfectly aligned when their center lines are coa the operating condition.

Figure 1: Coaxial Alignment Menu


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https://www.myodesie.com/index.php/wiki/index/returnEntry/id/2955 1 Alignment 1.1 Types of Misalignment 1.2 Causes of Misalignment 1.3 Effects of Misalignment 1.4 Indications of Misalignment 1.5 Alignment Tools 1.5.1 Dial Indicators 1.5.2 Parallels 1.5.3 Thickness Gauges 1.5.4 Micrometers 1.5.5 Miscellaneous Tools 1.6 Alignment Methods 1.6.1 Visual LineUp 1.6.2 Straightedge/Feeler Gauge 1.6.3 Rim and Face 1.6.4 Cross Dial 1.6.5 Reverse Dial 1.6.6 Laser 1.7 Alignment Preparation 1.8 Soft Foot 1.8.1 Effects of Soft Foot 1.8.1.1 Machine Frame Distortion 1.8.2 Distorted Bearing Housing 1.8.3 Types of Soft Foot 1.8.3.1 Air Gap or Parallel Soft Foot 1.8.3.2 Downward Bent Foot 1.8.3.3 Upward Bent Soft Foot 1.8.3.4 Squishy/Spring Foot 1.8.3.5 StressInduced Soft Foot 1.8.4 Measuring and Correcting Soft Foot 1.8.5 Soft Foot Analysis 1.8.6 Soft Foot Tolerance 1.9 Bar Sag 1.9.1 Measuring Bar Sag 1.9.2 Compensating for Bar Sag 1.10 Moving the Machine 1.10.1 Vertical Moves 1.10.2 Horizontal Moves 1.10.3 Bolt Binding 1.11 Precision Alignment 1.11.1 Rim and Face 1.11.1.1 Angular Misalignment Corrections 1.11.1.1.1 Procedure 1.11.1.2 Parallel Misalignment Corrections 1.11.1.2.1 Procedure 1.11.2 Cross Dial 1.11.2.1 Mathematical Solution 1.11.2.1.1 Graphical Solution 1.11.2.1.2 Procedure 1.11.3 Reverse Dial 1.11.3.1 Mathematical Solutions 1.11.3.2 Graphical Solution 1.11.3.2.1 Procedure

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It has been found that 50 to 70% of all vibration problems in machines are caused by misalignment. A thorough understandin what conditions create misalignment will help us understand what needs to be done to correct it.

Types of Misalignment

There are two basic types of misalignment: parallel (or offset) and angular. Both types can be found in the vertical and horizo planes. Typically, a combination of offset and angular misalignment is found in both directions, as shown in Figure 2. To achie goal, we must correct both types of misalignment in each direction.

Figure 2: Combination of Offset and Angular Misalignment

Two additional conditions must be addressed. The axial location of the machines and the baseplate are important to the operation. The proper shafttoshaft distance must be maintained, particularly when a limited end float coupling is being use shown in Figure 3.


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Figure 3: Maintain Proper ShafttoShaft Coupling

Torsional effect, or machine torque, may also need to be considered when aligning the equipment, as shown in Figure 4 may move horizontally during startup and operation. These are not entirely alignment subjects, but we should be aware of th importance when performing alignments.

Figure 4: Torsional Effect Talk Page

Causes of Misalignment The basic causes of misalignment are: Movement of one piece of equipment relative to another due to thermal growth in one or both machines. Piping strain or strain induced by electrical connections. Torsional movement taking placeat startup or while operating. Movement or settling of the foundation or baseplate. Inaccurate or incomplete alignment procedures (human error). Misboredcouplings.

Any one of the above conditions will dramatically affect the alignment of equipment. If more than one of the conditions exis odds are highly against a machine running smoothly, quietly, or for any appreciable amount of time. Only after all of the situa have been examined and corrected can a craftsperson be assured of an accurate alignment job being achieved and maintained. Talk Page

Effects of Misalignment The effects of misalignment are all around us in a facility. High noise levels or constantly vibrating floors are strong indications possible misalignment of machinery. Some of the other effects can be: Lost production Poorquality products Higher than normal repair orders Increased spare parts purchases and inventory on hand Reduced profits

In addition to the financial impact on the company, the direct effect on the various machine components can be considera Bearings will run hot, causing them to fail prematurely. Mechanical seals, seal rings, and packing will leak. Loss of product and lubrication can occur. Couplings will fail due to excessive strain on the hubs. In severe cases, shafts can break, causing exten damage to machines. Talk Page

Indications of Misalignment

Misalignment in rotating machinery can be detected in many different ways. Some methods are incorporated into the plants preventative maintenance program. Others are inspections that could be used on a regular basis but usually are performed the equipment has failed. Some of the indications of misalignment are: Wobbling shafts Excessive vibration Excessive bearing temperature Noise Bearingwear pattern Coupling wear Talk Page

Wobbling of the shafts can be observed without any instruments or tools. It indicates that the shafts are improperly lined up a need adjustment. Misalignment is one of the leading causes of equipment vibration. In spite of "selfaligning" bearings and fle couplings, it is difficult to align two shafts and their bearings so that no forces exist that will cause vibration. The significant characteristic of vibration due to misalignment is that it will be in both the radial and axial directions. If a bearing is found to h an abnormally high temperature and proper lubrication is present, then misalignment is probably the cause. Turbines, pumps other plant equipment have bearing temperature monitors or indicators. It is best to refer to the manufacturers literature for th correct bearing temperature parameters. Some pumps and smaller equipment do not have any monitoring devices. For thos placing a hand on the bearing is a good indicator of excessive bearing temperatures. If the bearings on a particular pump a hotter than the bearings on similar pumps, misalignment could be the cause. Due to the possibility of the presence of high


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temperatures, care must be taken when touching bearings. Like vibration, noise can be detected simply by noticing a chang the equipment sounds during operation. All running equipment produces a certain normal amount of noise. Only if an opera familiar with normal equipment noise will they be able to detect abnormal sounds. Possible misalignment may be detected t bearing and coupling inspections. If bearings show signs of excessive wear, misalignment usually is the cause. The bearings w to be replaced and the alignment corrected to prevent further bearing damage. The coupling parts should also be inspecte sign of excessive wear, especially if the wear is uneven, is a good indication of misalignment.

Alignment Tools

There is a multitude of methods available to perform accurate alignment, any of which can deliver the desired result. Howev several precision tools are commonly used in alignment work. dial indicators, parallel blocks, taper gauges, feeler gauges, a t measure, a 6inch rule, and a small mirror are all useful. Each one has a part to play in doing alignments.

Dial Indicators

Dial indicators are probably the most widely used precision tools. They are available in various styles, sizes, and range. A back plunger type, shown in Figure 5, is often used to take rim and face readings on couplings, to measure soft foot, and to monito accurate machine moves. Their small size makes them easy and convenient to use.

Figure 5: Bottom and Back Plungers

Bottom plunger style indicators are used for taking runout readings on couplings and shafts, and for measuring misalignment. come in two styles: balanced or continuous reading. Examples of both are shown in Figure 6. The dials are 1 inches in diamete 1/8 inches in diameter. Their usable range is from 0.250 inch to as much as 12 inches. Typically, a 0.0250inch or 0.500inch trav indicator is used in alignment work.

Figure 6: Balanced and Continuous Reading Plunger Talk Page

Parallels

Adjustable, or sliding, parallels, shown in Figure 7, are used to measure gaps or holes. They usually are available in sets. Sliding parallels vary in length from 1 to 5 1/16 inches, are 9/32 inch thick, and can measure ranges such from 3/8 inch to 1 to 2 inche check the size of a gap, the sliding parallel is inserted and expanded to the proper size. The parallel then is measured with an outside micrometer to determine the gap size. Sliding parallels can be used to take coupling hub face readings.

Figure 7: Sliding Parallels Talk Page


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Thickness Gauges

The standard thickness gauge, also called a feeler gauge is a compact assembly of highquality, heattreated steel leaves o various thicknesses, as shown in Figure 8. The leaves usually vary in thickness by .001 inch, and the exact thickness of each lea marked on its surface.

Figure 8: Thickness Gauge

A thickness gauge is the measuring instrument commonly used to determine the precise dimension of small openings or gaps as those that must be measured in the course of aligning a coupling. To determine the dimension of an opening or gap, the s leaves are inserted singly or in combination until a leaf or combination is found that fits snugly. The dimension is then ascertain the figure marked on the leaf surface or, if several leaves are used, by totaling the surface figures. Another type of thickness g not as widely known or used but ideally suited for coupling alignment, is the taper gauge, shown in Figure 9. It is sometimes re to as a gap gauge. Its principal advantage for coupling alignment is that it gives a direct reading and does not require triala error "feeling" to determine a measurement. The tool end is inserted into an opening, or gap, and the opening size is read on graduated face. Two measurement systems inch and metricare shown.

Figure 9: Taper Gauge Talk Page

Micrometers Another precision measuring instrument used for coupling alignment is the outside micrometer caliper shown in Figure 10 name implies, it is used to measure outside dimensions.

Figure 10: Micrometer Caliper

Outside micrometers are available as single units or as complete sets. A complete set of micrometers gives you the advantag being able to quickly choose the micrometer appropriate for a specific situation. Two types of micrometer sets are generally available. One contains many micrometers of different sizes with a variety of frames. Such sets may contain anywhere from 3 micrometers and have ranges varying from 0 to 3 inches up to 0 to 24 inches. Different combinations of a ratchet stop or frict thimble and lock nut may be provided on micrometers in these sets. Micrometer sets of this type may be graduated in thousa of an inch, tenthousandths of an inch, or hundredths of a millimeter. The second type of outside micrometer set, illustrated in 11, contains an outside micrometer with interchangeable anvils and a set of standards. Micrometers of this type range from 0 inches up to 20 to 24 inches and are also available with Metric calibrations. An outside micrometer with interchangeable anv frequently used in the field to measure objects of varying sizes. The micrometer has an adjustable stop on the anvil to alter the overall anvil dimensions. Both types of micrometer sets are capable of measuring within the same size range and producing r


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Figure 11: Outside Micrometer with Anvils Talk Page

Miscellaneous Tools

Another useful and necessary tool needed when doing alignment work is a tape measure. This is a common item to most craftspeople, so a detailed description is not needed here. Your 6inch pocket scale is very likely the alignment tool you are m familiar with. Many of your alignment jobs will be performed with this device. This type of alignment has its place, but it is not a precision method. A small mirror is another very helpful item to have in your toolbox. It is very handy when trying to read an indicator that may be positioned in a location that is inaccessible. Shims are very likely the most important tool used when performing alignments. Proper placement and accurate thickness are the most crucial elements of using shims. Using precut stainlesssteel shims is rapidly becoming the preferred way of making vertical elevation changes. They are very easy to use, q install, and usually accurate in their exact thickness. Talk Page

Alignment Methods

It is obvious there are many methods available today to align machinery. Almost all of these methods originated over 30 yea The concept of alignment is not new; it is just not understood by most people who actually perform the alignment. The purpo this section is to familiarize the technician with the most common methods used today. All of these methods will be described detail later in this manual. As with any method, there are potential sources of error as well as advantages. This section points o some of the more salient aspects for each method. The methods we will cover are: Visual LineUp Straightedge/Feeler Gauge Rim and Face Cross Dial Reverse Dial Laser Talk Page

Visual LineUp

The visual lineup method, shown in Figure 12, is the most common method of alignment. Used in initial installations, visual line allows technicians to analyze the working conditions and feasibility of installation.

Figure 12: Visual LineUp Method Talk Page

Straightedge/Feeler Gauge

Straightedges are used to determine the offset between coupling halves; this is shown in Figure 13. Corrections are made und four of the machines feet. Feeler gauges or taper gauges measure the gap between coupling halves at the bottom and top coupling.


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Figure 13: Straightedge/Feeler Gauge

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Rim and Face

This method is similar in principal to using a straightedge and feeler gauge, but more accurate since dial indicators are used. rim reading measures the offset between the coupling halves. The face reading measures the angular difference between th faces of the coupling, as shown in Figure 14. Changes are calculated with the same formula as the straightedge/feeler gaug method.

Figure 14: Reading Angular Difference Between Faces Advantages: Used when onlyone shaft can be rotated. Given the correct precautions, precision alignment is attainable with this method. Disadvantages: Endfloat affects face reading. Indicator bracket (bar) sag affects readings. Eccentric, skewedcouplings or damaged surfaces will cause errors. Fixture looseness causes errors. Indicator stems not perpendicular to shaft causes errors. The indicators should be checked to ensure that: The plungers are level, parallel to shafts, and depressed about half their total travel. The indicators are same distance from the shaft axis and exactly opposite each other when two indicators are used. The contact points are midway between coupling halves in the axial direction. If sagfree brackets are not available, sag greater than .001 inch must be compensated for. Talk Page

Cross Dial

This method uses two dial indicators mounted exactly 180 apart to take shafttoshaft readings. Both parallel and angular misalignment may be compensated for at the same time. This method allows the couplings to remain attached, as the shafts move together. Figure 15 show a typical cross dial setup.


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Figure 15: Cross Dial Setup Advantages: Very accurate method of using dial indicators Easy and fast to use Simple: Graphical calculations for misalignment are nontechnical Computer or pocket calculators can also be used Sources of error are: Indicator stems must be perpendicular to the shaft Looseness Indicator bracket (bar)sag Coupling backlash Extreme axial float Indicators that are not exactly opposite each other Talk Page

Reverse Dial

This method uses two dial indicators that take shafttoshaft readings and is almost the same as the cross dial method, except the indicators are in the same plane with each other. Both the offset and angularity are combined in the alignment calculati This method, shown in Figure 16, determines the misalignment by taking two rim readings at different points along the shaft.

Figure 16: Reverse Dial Method Advantages: Most accuratemethod of using dial indicators Easy and fast to use Simple: Graphical calculations for misalignment are nontechnical Computer or pocket calculators can also be used Requires only 180 rotation Sources of error are: Indicator stems not perpendicular to the shaft Looseness Indicator bracket (bar) sag Coupling backlash Extreme axial float Talk Page

Laser

The laser method of alignment is similar to the rim and face method, but it uses light to span the shafttoshaft distance. As bo


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shafts are rotated, the misalignment is determined by the movement of the laser beam on the detector surface. This is shown Figure 17.

Figure 17: Laser Method Advantages: Most accurate measuring device available Speed: with practice, alignment calculations can be made quickly Wired to a computer Only requires 180 shaft rotation Horizontal move capabilities Sources of error are: Heat/cold air can distort the laser and affect alignment calculations Looseness in brackets or fixtures Coupling backlash

Proper shaft alignment is required to maintain operational longevity of all rotating machinery. The two basic types of misalign are parallelism and angularity. Both types can be found in the vertical and horizontal planes. To achieve our goal of proper s alignment, we must correct for both types of misalignment. It has been noted in this section that 50 to 70% of all vibration pro in rotating equipment are caused by misalignment. The overall effect of this misalignment is lost production, poor quality of products, higher repair costs, and increased spare parts, all of which lead to reduced profits. We also discussed the tools used alignment. It is very important that we know how to use these tools. In the sections that follow, we will learn how to use the information as well as the tools to properly align a piece of equipment. Also, each of the alignment methods will also be discu in detail later in this manual. Talk Page

Alignment Preparation

Before the alignment process can begin, several things must be examined and corrected. If a precision alignment is attempt while any of these conditions has yet to be rectified, accurate results will be unobtainable. If any one of these items is overloo ignored, the effect on the machine could be an unscheduled or emergency shutdown. The machine could even be heavily damaged. A prealignment checklist is also designed to save time in performing alignments, as 90% of the problems involved alignment can be avoided by following the prealignment checklist. These checks should be completed every time an alignm performed. You do not need to follow the order of the list, but each point needs to be checked.

Before shutting the machine off, take temperature readings in the planes of the feet for both machines to determine if machine is subject to thermal growth. Check the service history for any information that may be useful. Lockout/tagout the machine to be worked on. Ensure the safety of all individuals. For pumps, close the suction/discharg valve to protect against pump backspin. Clean up around the machine. Loosen the mechanical seals or packing. Before the rotating shafts, make sure that the bearings are properly lubricated with the correct type and amount of gre oil. If an auxiliary oil system is used, make sure it has been serviced. Rotate the shafts slowly. Listen/feel for binding/roughness. Always rotate in the direction of equipment rotation to preve backlash in couplings and gearboxes. Check the machine for worn or defective bearings. Check the coupling for the following: Looseness (grids, teeth, disks or elastomers, etc.) Fit on shaft (taper or straight bore) Eccentricity (runout) Worn grid/teeth members Correct lubricant type and amount Setscrew tightness Proper key length Match marks in the correct place Proper bolts and washers: note length, machining, weight Check shafts on both machines for: Concentricity (runout) Movement in the axial, horizontal, and vertical directions greater than the manufacturers allowable limits Smooth fixture to mounting surface (pipewrench footprints)


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https://www.myodesie.com/index.php/wiki/index/returnEntry/id/2955 Inspect machine base and foundation for cracks, warped surfaces, and corrosion. Clean base (near feet) of rust and other foreign matter.

If carbonsteel shims are used, remove and replace with precut stainlesssteel shims. Remove and replace any shims th may be cracked, bent, folded, rusted, handcut, brass, or otherwise defective. Whenever possible, start with 1/8 inch (0.125 inch) of shim under each foot to allow for vertical adjustment. Ensure the axial position of the machine is correct and that the coupling will allow both machines to run in their respect axial positions. Find and mark the magnetic center on motors that have axial end float (sleeve bearings). Check for pipe and/or electrical connection strain if possible (roughin stage). : Ensure both the vertical and horizontal jack bolts are loose. Lubricate for smooth operation. Remove dowel pins from both machines. Check and remove any soft foot for both machines. Ensure all bolts on both machines are torqued. Note the bolt lubrication and remove any "bell/cupped" washers. Determine alignment method to be used. Assemble fixtures and check for accuracy and working condition. Take machine dimensions. Talk Page

This list is not meant to be a complete systematic procedure. There may be more specific checks required at different facilitie while others may not apply. The objective is a thorough examination of the condition of the machine before attempting a pr alignment. Without these checks, precision is not obtainable.

Soft Foot

Soft foot is a term that many people have heard, yet is widely misunderstood. Historically, soft foot has been considered insignificant and only a minor cause of machine vibration. Not until recently have specialists begun to understand that a considerable amount of machinery vibration is caused by presence of a soft foot condition. This subject can be considered separately from alignment, yet the effects of soft foot are so prevalent in the alignment process that it must be eliminated be making any alignment corrections. The prealignment checks and procedures include eliminating soft foot; however, it is adv that soft foot be checked in each stage of the alignment process. The reason soft foot is difficult for many technicians to elim is that the causes of soft foot are not clearly understood. Common measurement practices do not give a complete picture o actual soft foot condition. What exactly is soft foot? The term has several other names, such as soft leg or rubber leg, but ther adequate definition that accurately describes the situation. Perhaps a description in nontechnical terms will be helpful in cla the problem. Have you ever sat down at a table in a restaurant and found that the table rocks when you lean on it One leg i shorter than the other three, and the table does not rest evenly on the floor. The table has a soft foot. When this occurs, the lo solution is to find some type of shim pack, which in most restaurants is usually a book of matches, and place it under the foot touching the floor to correct the rocking motion. Similar situations occur with rotating equipment where the feet of a machine not rest evenly on the base. It is identical to the table; however, the movement is measured with dial indicators or feeler gaug Tightening the holddown bolt can create enough force to close the gap between the foot and the base and appears to co the problem, but this is where problems actually begin. As shown in Figure 18, the term "soft foot" does not necessarily describ actual condition of the foot because the foot is not actually soft. Soft foot is defined as a condition where the machines feet lie in the same plane as the base.

Figure 18: Soft Foot Talk Page

Effects of Soft Foot

For the purpose of our discussion, we will use the term "soft foot," understanding that the condition can be called by several o names.

Machine Frame Distortion

Machine frame distortion is the result of changes that occur internally or externally to the frame of the machine. This often ca shaft deflection or movement as the holddown bolt is tightened when a soft foot condition exists. Machine frame distortion is easily explained with a simple soft foot example. Consider a machine with a soft foot condition. With the holddown bolts loo one foot does not rest on the base. There is no internal stress on the machine in this state. This is shown in Figure 19 by the strai horizontal lines across the machine.

Figure 19: No Internal Stress

Tightening the holddown bolt will draw the foot down to the base, closing the gap. However, this creates stress in the machin


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https://www.myodesie.com/index.php/wiki/index/returnEntry/id/2955 frame, as the curvature of the lines on the machines frame now show in Figure 20.

Figure 20: Stress Induced by Tightening the HoldDown Bolt

The distortion of the machines frame can have multiple effects on the shaft position. The shaft position can change when the down bolts are loosened and tightened if a soft foot condition exists. Using proper torque values and patterns for holddown as shown in Figure 21, is helpful, but it cannot completely eliminate the variation in shaft movement.

Figure 21: Proper Torque Pattern for HoldDown Bolts Talk Page

Distorted Bearing Housing

In other situations, machine frame distortion can distort the bearing housing. This can result in excessive wear on the top and bottom of the outer race. Forces due to soft foot usually will act 180 apart, creating a preloading condition on either side of t bearing. Changes in the shaft position due to soft foot can create other problems internal to the machine. The distortion may change the position of one of the bearings, causing increased wear. Machine frame distortion can also create internal misalignment between the bearings. Tightening the holddown bolt causes a distortion of the machines frame, creating an o between the bearings. The angle the shaft makes between the inboard and outboard bearings actually causes internal misalignment between the bearings. Figure 22 shows a distorted bearing.

Figure 22: Distorted Bearing Talk Page

Types of Soft Foot The various types of soft foot are described, in detail, below.

Air Gap or Parallel Soft Foot

The most common explanation of soft foot is parallel or straight soft foot. When the holddown bolt is loose, the foot simply do reach the base, leaving a gap between the foot and the base. The bottom of the foot is parallel to the baseplate though. Th condition is easiest to detect using either a feeler gauge or dial indicator, as shown in Figure 23.


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https://www.myodesie.com/index.php/wiki/index/returnEntry/id/2955 Figure 23: Parallel Soft Foot Talk Page

Downward Bent Foot

A common situation is known as a bent foot. Here the foot is touching the base on the outside portion, but the inside of the fo bent, creating an angle between the base and the bottom of the foot. When the holddown bolt is tightened, the foot will de and distort the machine frame, depending on what portions of the frame will flex, as shown in Figure 24.

Figure 24: Downward Bent Foot Talk Page

Upward Bent Soft Foot

The foot may also be bent upward so that the outside edge is not touching the base and the deflection occurs along the ou of the foot. Figure 25 shows that tightening the holddown bolt will result in a distortion of the machines frame as the inside of foot is drawn down to the base. Either of these situations can cause frame distortion; however, an inconsistent or warped bas have the same result as a bent foot.

Figure 25: Upward Bent Soft Foot Talk Page

Squishy/Spring Foot

A new deck of cards stacks shorter than an old deck, not because the cards are thicker, but because of the buildup of oil an on each card and the bending and creasing of the cards. The same holds true for shims. Grease, dirt, rust, paint, metal filings other substances can build up the thickness of a shim. Bending and creasing can cause a stack of shims to give under pressu illustrated in Figure 26.

Figure 26: Squishy/Spring Foot

Talk Page If these factors are multiplied by several shims, the shim pack can actually have a spring effect. The foot will move when the h down bolt is tightened or loosened. A soft foot condition exists even though there is no gap because the foot moves when th is tightened.

StressInduced Soft Foot https://www.myodesie.com/index.php/wiki/index/returnEntry/id/2955

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Perhaps the most difficult soft foot condition to detect is caused by forces that are external to the machine. This is referred to stress or forceinduced soft foot, illustrated in Figure 27. It can be the result of pipe strain or stresses induced by the electrical connections as well as drastic misalignment. Binding at the coupling can also induce external forces that create a soft foot condition.

Figure 27: StressInduced Soft Foot

Stressinduced forces can be created during any stage of the alignment process; therefore, eliminating this kind of soft foot m require more than one check. Soft foot can be a major problem. If alignment is attempted on a machine with a soft foot con inconsistent readings will make the alignment calculation difficult regardless of the alignment method used. Throughout indus most alignments are performed without checking for soft foot. The main reason for this is incomplete analysis and the results a hours of frustration, compromised alignments, and machines that do not run as smoothly as possible. If soft foot is corrected a alignment is complete, any shim changes may change the alignment. To have smoothrunning machines, soft foot must be eliminated on both the drive and driven machines before performing the alignment. Understanding the different types of soft essential in examining the various methods of measuring and correcting soft foot deflection causing machine frame distortion Some methods do not always accurately measure soft foot, and if the craftsperson does not completely understand the prop procedure, a soft foot condition may go undetected. Talk Page

Measuring and Correcting Soft Foot

In ideal circumstances, the baseplate and feet are machined flat to within one mil when the machine is installed. In most situ however, the base is not a level surface, and the amount of soft foot can change depending on the location of the machine on the base. Since any movement of the machine on the base may change the soft foot, a roughin alignment must be perf before checking for soft foot. It is possible for soft foot to change during the alignment process, so there will be some going b and forth between correcting the misalignment and checking for soft foot during an alignment. Soft foot changes, which occ during the moves of the adjustment and precision alignment stages, will be checked at that time. Once the machines are in approximate final positions, a roughin soft foot can be performed. The procedure for an initial soft foot determination is as fo

1. Loosen all the holddown bolts and check for any gaps under the feet using a feeler gauge, as shown in Figure 28 2. Eliminate the gap under the foot by placing the largest single shim that will close the gap under each foot without raisin machine. 3. If a gap still remains, place additional shims under each foot to close the remaining gap.

Figure 28: Checking for Soft Foot

For residual soft foot, simply slide the shim into position under the foot until stops. Do not force the shim into place, as thi raise the foot and can create soft foot at other feet. The purpose of the roughin soft foot is to eliminate any gap under foot. It has been found that a roughin soft foot check can eliminate as much as 90% of the soft foot present in a mach Once the roughin soft foot is complete, along with all of the other prealignment checks, the technician is ready to mo to the adjustment stage of the alignment. We want to check for soft foot a second time after all of the adjustments hav been made to be certain that we have not introduced any stress or forces on the machines frame that will create a so condition. With the roughin soft foot complete, all of the holddown bolts should be tightened to the proper torque


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specification once the alignment has been checked in the adjustment stage. It is common practice at this point to che soft foot by loosening one bolt at a time and measuring the deflection using a feeler gauge or basemounted dial indic The procedure for checking each foot is to loosen each holddown bolt one at a time, leaving the others tight. Place a mounted dial indicator on the foot so the dial is perpendicular to the top of the foot for an accurate reading. Be sure th stem of the dial is not in the way of the bolt or wrench. If the dial is bumped with the wrench when loosening the bolt, th readings will be inaccurate. With the dial in position, adjust it to zero and then loosen the holddown bolt. The amount o foot deflection will be measured on the dial indicator. Notice this will always be a positive number, as the foot will move from the base, pushing the stem of the dial in and giving a positive reading. If the dial shows a negative number, check deflection of the base or movement of the indicator support. In many situations, it is difficult to position the dial indicato the foot because there is little clearance between the foot and the machines frame. When this occurs, a feeler gauge be used to measure the gap under the foot, as shown in Figure 29.

Figure 29: Checking for Clearance with a Feeler Gauge

Talk Page Adding the shim thickness equal to the amount read on the indicator or by the feeler gauge will not always eliminate the soft In many cases, the whole foot does not deflect by the same amount; as we have seen, there are several types of soft foot deflection. Indicators can give erroneous readings if the machine is mounted on a thin baseplate that moves when the foot h down bolt is tightened and loosened. Therefore, it is recommended that both indicators and feeler gauges be used if they ar available. We want to check every foot on both machines for a soft foot deflection before making corrections. If you simply c a foot and then add shims, you may be creating more problems than you are eliminating. This process will eventually accom the goal of removing the soft foot, but the entire process is much faster and easier if the worst foot can be identified first. Quit often, eliminating the largest soft foot will remove the soft foot at the other feet. Therefore, we want to check all of the feet individually before making any shim corrections. In the previous section, we examined the effect on the shaft position due to foot deflection. This was shown to have a considerable impact on the movement at the coupling. Therefore, once the initial foot is eliminated in the roughin stage, we want to determine if there is any shaft movement caused by the remaining soft fo

Soft Foot Analysis

With the information gathered using indicators and feeler gauges, it is possible to analyze any situation and determine the be to eliminate soft foot from the entire machine. All the information should be gathered before any shim changes are made. Ta few minutes to examine the soft foot on the entire machine can save hours of tedious soft foot correction. The best method f eliminating soft foot is to have the base and bottom of the machines feet as flat and smooth as possible. This requires more tim preparation, but the time saved in eliminating soft foot problems later makes this the best approach.

Soft Foot Tolerance

We have reached the point in our discussion where we must talk about the real world. We all know that things look much bet paper than they do in the field and there are always going to be those things that we just cannot fix. Eliminating all of the sof our goal, but when we have time restrictions or encounter difficult problems, we need to have some criteria that can be used tolerance guideline for removing soft foot. Many tolerances suggest 2 or 3 mils as an acceptable reading, but is this close eno With the measuring devices available today, every attempt should be made to achieve soft foot corrections as close as poss proper soft foot readings are taken on a solid base, we should be able to eliminate any readings above 1 mil. Keep in mind t is an art, not a science; we want to remove as much soft foot as possible. If, for some reason, we cannot get the soft foot bel mil, this should be recorded. There may be practical limitations that will not allow you to achieve tight tolerances even after thorough measuring and analysis. If the base, feet, or legs of the machine are too flexible, final adjustments may cause more frustration than results. Reinforcing the base may be necessary before precision soft foot correction can be accomplished. A foot that can be removed with reasonable time and effort will make the alignment process faster, easier, and more effective Talk Page

Bar Sag

Bar sag is simply the effect of gravity on a fixture. This effect can be measured accurately. As it affects the final accuracy of t alignment, it must be accounted for in your readings or eliminated from your fixtures before taking indicator readings. Talk Page

Measuring Bar Sag

A certain amount of sag exists in most brackets. This amount must be known before attempting to align the couplings so that sag can be calculated into the indicator reading. A procedure for determining the amount of sag in a bracket is as follows: 1. Assemble the bracket on a shaft or a lathe, as shown in Figure 30, then set up the indicator on top and zero the dial.


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Figure 30: Bracket Assembles on a Shaft

2. Turn the complete assembly 180 and take a reading on the bottom. This reading is the amount of sag for that particular set Remember, the test should be as near as possible to the actual setup because a change in the distance between the shaft a the bracket may change the amount of sag. :Where two indicators are to be used, both indicators must be assembled on th brackets before zeroing on top.

3. Keep a record of the amount of sag for each setup for reference when calculating the actual indicator readings. If the am of sag is greater than .001 inch, it is subtracted from the vertical readings. Talk Page

Compensating for Bar Sag

Before we can determine the amount of bar sag, we must first be able to get repeatability from the fixtures. The best way to d is to set the dial to zero at the 12 o'clock, or top, position, rotate the machine or bar one full 360o, and see if the indicator still zero at the top. If there is more than one mil or 0.001inch showing on the indicator, there may be some looseness in the fixture may need to tighten up the fixture parts or make additional changes in the fixture configuration until you can get repeatable readings. This is very important to the accuracy of your alignment calculations. Once the amount of bar sag has been determ for the fixtures you are using, it can be handled in one of two ways. The first possible method is to simply add the amount of b to your indicator readings. Because the sag is always a negative value, it can be added to the total indicator readings. The exception to this is that indicators starting at the 6 o'clock position and moving to the 12 o'clock position must have the bar sa subtracted from the final reading. This would be the case for one dial in the cross dial method. A second method is to simply the amount of bar sag determined at the 6 o'clock location into the 12 o'clock position as a positive number, or set the dial a o'clock position to a negative value. For example, if you have assembled the fixtures on a pipe or piece of bar stock that rep two shafts in perfect alignment, as shown in Figure 31, and adjusted the indicator to zero at the top, or 12 o'clock position, the rotated the fixtures so that the indicators are now at the 6 o'clock position, you should get a negative reading on the indicato a minus 8. Now rotate the fixture back to the 12 o'clock position. Dial the minus 8 into the indicator as a positive value, or as p To confirm that you have properly compensated for the bar sag, rotate the fixtures back down to the 6 o'clock location. The indicator should read zero.

Figure 31: Compensating for Bar Sag

Talk Page When you place the fixtures back on the shafts of the machines being aligned, set the dial at the top to positive 8. When you the fixture down to the 6 o'clock position, the number you read is the total indicator reading of the amount of misalignment. T bar sag has been compensated for, and the indicator now gives you the amount of difference between the two machine sh centerlines. This section covered items that must be corrected and/or accounted for before performing a precision alignmen Items such as casing strain, cracked foundations, and soft foot will defeat the purpose of performing an alignment in the first Bar sag, when unaccounted for, will cause errors during the alignment process or lead us to believe a machine train is aligne when it actually is misaligned.

Moving the Machine

Any instruction on precision alignment of rotating equipment must include methods for making accurate, controlled moves o machine. There is a multitude of ways to move a machine. Some are better than others with possibilities ranging from using la hammers or pry bars to using hydraulic wenches or finethreaded, smoothoperating devices. Any alignment method, regard its accuracy in measuring the misalignment, is useless if we do not take the proper precautions and procedures in order to ac precision movement of the machine. All of the work in taking accurate readings can be lost in a split second if the proper techniques are not applied. In this section, we will examine many of the procedures and methods used to ensure an accurat


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alignment. There has been some discussion among alignment specialists about which move should be made first: the horizon the vertical move. Once the machine is adjusted to its proper vertical orientation, a slight move in the horizontal direction sho not change the vertical alignment. This is the procedure once the rough alignment and adjustment stages are complete. Ho certain situations may require a horizontal move be made first in order to attain accurate indicator readings if the alignment been changed during the adjustment stage. In any alignment process, there may be some going back and forth from the ve to the horizontal until the alignment is completed and precision is achieved.

Vertical Moves

As with all vertical moves, using a dial indicator is not necessary to determine the change in the vertical direction, but it can b helpful to check for any soft foot created when moving the machine. By using a micrometer, the exact thickness of the shims installed can be determined for the required alignment correction. Be sure to mic every shim that is installed. Do not believe w printed, stamped, or etched on the shim. Always check the shim to be sure. When loosening the holddown bolts, the first precaution is to loosen only two bolts at a time when making any shim change. If you loosen all the holddown bolts at the sa time and then raise the machine, the entire configuration at the feet may change. This is particularly true if any of the feet ha been corrected for soft foot conditions using a tapered or step shim. Leaving two holddown bolts tight reduces the chances uncontrolled move. Any uncontrolled movement of the machine may change the horizontal, axial, and even the vertical positioning of the machine, thereby negating all your previous work. Loosen the bolts on either the left or the right side of the machine, but not both sides. Raise one side of the machine just enough to make the shim change. If the machine is raised to it can bend the feet on the side of the machine where the holddown bolts are tight. Make the necessary shim change and down the bolts to their proper torque value. Repeat the process for the other side of the machine. Each tightening of any bo the machine should be treated as though it is the last time to work on that particular bolt. For all vertical moves, be sure to ra machine just enough to add or remove the desired amount of shims. Any excess movement of the machine in the vertical di can result in a bent foot. Once you have the machine raised enough to make the shim change, remove the shims from underneath each foot and add or subtract the amount of shims you have determined. Always use the least number of shims a foot as is practical. The more shims under a foot, the more likely a spring effect or soft foot is to occur. If possible, make or u single piece of shim the total thickness required under the foot. If this is not possible, a maximum of three to four shims should b limit. This gives the foot a solid place to rest on and reduces the possibility of anything getting between individual shims. When making shim changes for the vertical alignment, it is important to remember the shims must be placed beneath those shims t are present to correct for soft foot. If the shims used for correcting the vertical alignment are placed on top of the soft foot sh can create more soft foot problems. When inserting the shims under the feet, insert the shims slot all the way in until the shim h "bottomed out" in the slot. You should then pull the shim back about a quarter of an inch before tightening the bolt. If you lea shim inserted all the way into the threads, tightening the bolt will pinch the end of the shim and may affect the accuracy of t shim change. After completing the shim changes and tightening the holddown bolts, another set of readings should be take the method used in the alignment calculation. If the move is within the specified tolerance, proceed with the horizontal move second move is required, determine the necessary shim change and make the correction. Talk Page

Horizontal Moves

If the base plate has jackbolts installed, the task of moving the machine is made much easier. In many situations, it is best to h jack screws installed at the time of the alignment rather than trying to move the machine some other way, which is often mo difficult and requires more time. Figure 32 shows a foundation with jacking screws installed.

Figure 32: Foundation with Jacking Screws Installed Before any of the holddown bolts are loosened, all of the jackbolts must be loosened on the machine. Any unequal pressure jackbolts could result in an uncontrolled move and require the technician to take another set of alignment readings. When loosening the holddown bolts, back them off just enough to allow the machine to slide sideways. Since it takes very little pres on the jackbolt to move the machine horizontally, there is no real need to completely back off or remove the holddown fast If a graph is constructed determining the position of the misaligned shaft, you will know exactly which direction to move the machine. Another way to avoid confusion is to always look from the machine toward the machine. Everything to the right, or toward the 3 clock position, is in the positive direction. Everything to your left, or toward the 9 clock position, is in the negative direction. This should help you visualize the proper direction for the move. The preferred and most accurate method for measuring the horizontal move is to place dial indicators around the machine in the planes of the feet, as shown in Figure 33.

Figure 33: Place Dial Indicators Around the Machine It is important that the indicators are positioned on the machine in the location used in the alignment calculation. As shown in Figure 34, this usually is the center of the holddown bolt and at the approximate shaft height.


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Figure 34: Place Indicators in the Location Used in the Alignment Calculation The procedure for performing a horizontal move of a machine is as follows:

1. Position the basemounted dial indicators in the location of the machines feet or at the point determined from the align calculation. 2. Adjust the dials to zero. 3. Move the machine in the proper direction by the determined amount, making sure all of the dial indicators agree. ' Figure 35 shows the proper dial indicator setup.

Figure 35: Proper Dial Indicator Setup No matter what device or method is used to move the machine, it is very important to have control of the machine. The mos common problem encountered when moving the machine horizontally is that there are no jackbolts on the machine to main this control. If no jackbolts are installed, small hydraulic jacks can be used to move a machine if they are backed up to a solid structure, such as a beam, a solid wall, an adjoining pedestal, or a base. A chain fall or comealong can also be used. Again must be secured to something solid or immovable and operated one click at a time. Another very good idea is to use pony c or pipe clamps, as shown in Figure 36, attached and operated to smoothly move the machine in the desired direction.

Figure 36: Using Pipe Clamps Talk Page

Bolt Binding

At this point in the alignment, you may be thinking, "Ive got it now." There is; however, another problem you may encounter. F those of you who have been in this business for any time at all, you know that being boltbound happens quite often. This hap when the required horizontal move is greater than the amount of clearance in the foot. The most common solution, although the preferred solution, is to mill down the bolt or "Chicago" the bolt. By removing the excess material along the shank portion bolt, you can gain many thousandths of an inch, which may allow you to reach the proper horizontal position for the machin shown in Figure 37.

Figure 37: Bolt Binding The only precaution that must be pointed out is: do not turn the diameter of the shank down to less than the diameter of the the threads on the bolt. If too much material is removed, it will greatly reduce the holding strength of the bolt, possibly allowin break when tightened. Another possible option is to install the next size smaller bolt in the place of the boltbound foot if a thr hole is present. For situations where the base has a threaded or blind hole, a helicoil can be installed. Before doing this, it is a idea to check whether the next smaller bolt will provide enough holding force without creating a problem for the machine. U one bolt of a smaller size on one holddown point of a machine will not create a safety hazard, but it is a good idea to check


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an engineer, supervisor, or foreman before proceeding with this option. Another common practice is drilling out the hole in th just enough to allow the machine to move over further. If you use this method, be careful to make sure that the hole does no exceed the size of the washer. If the washer is too small for the hole, it will bell or cup out of shape when the bolt is tightened, shown in Figure 38. To avoid this, you can place the next size larger washer below the correctsized washer for the bolt being or use a piece of steel plate. Usually a piece with inch thickness is large enough to cover the enlarged hole in the foot. Drill a the plate slightly larger than the bolt diameter.

Figure 38: Belled Washer A bent bolt will have the same effect. When the bolt is tightened, it will have an elliptical or cam action and can move the machine out of alignment, as shown in Figure 39.

Figure 39: Bent Bolt Talk Page

Precision Alignment

There are three methods currently used to calculate the amount of shim changes and horizontal moves required to achieve accurate machine alignment. They are each capable of arriving at the same results by use of mathematical formulas and/o graphical solutions. There are various tools that are available to help in the process. The first is a simple pocket calculator. Wit proper formula and a basic understanding of the alignment process, accurate machinery movement can be achieved. The second method available is the graphical solution. This method uses simple 10 x 10 piece of graph paper that gives a pictoria representation of the machines and the amount of movement needed to correct the misalignment. The third method is the u a computer, either a desktop or a special computer designed specifically for the alignment task. In this section, graphical an mathematical solutions to misalignment are discussed. We mentioned the computer method only to make you aware of its existence. The following are the methods of alignment that are discussed and their methods of solution: 1. Rim and Face (Mathematically Only) 2. Cross Dial (Mathematically and Graphically) 3. Reverse Dial (Mathematically and Graphically) Talk Page

Rim and Face

The rim and face alignment method is commonly used where space considerations would prevent the use of the cross dial o reverse dial methods. It also is the only method that can be used when rotation of both shafts cannot be accomplished. The of the misalignment can only be calculated mathematically, and parallel and angular misalignment must be calculated separately. After the rough alignment is done, the angular misalignment should be removed before solving for the parallel misalignment. For this reason, the rim and face method is often more time consuming than the other methods available. Talk Page

Angular Misalignment Corrections

The face dial is used to measure the distance between the coupling faces. This measures the angular misalignment in both th horizontal (3 o'clock to 9 o'clock position) and the vertical (12 o'clock to 6 o'clock position) planes. The total indicator reading the actual difference in distance between the coupling faces. Because of the dial position relative to the face of the couplin sag will not have an effect on face readings. It will still be an issue to consider when taking rim readings though. Figure 40 typical setup for taking the face readings.


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Figure 40: Face Readings Talk Page

Procedure 1. 2. 3. 4.

Zero the dial indicator at the 12 o'clock position (3 o'clock position for horizontal moves). Rotate the indicator 180 and read the error from the difference in reading. Measure the coupling diameter of indicator travel. Measure the distance between the coupling face and the front foot and the rear foot.

5. Calculate proper shim movement (or horizontal movement) with the following formula:

Example 1:Rim and Face Angular Misalignment Calculation Given the following information and Figure 41, calculate the required shim moves to achieve perfect angular alignment. Face Reading @ 12 o'clock: .000" Face Reading @ 6 o'clock: .072

Figure 41: Example One

Solution: These calculations tell us that, to achieve perfect angular alignment, it will be necessary to remove .216 inch from th foot and .360 inch from the rear foot. Negative numbers will always indicate that shims need to be removed, while positive nu are an indication that shims will need to be added.

Talk Page

Parallel Misalignment Corrections

The dial indicator positioned to take the rim readings will measure the amount of parallel offset misalignment. The total indica reading is always double the actual offset. Therefore, any shim moves to correct parallel offset misalignment will always be ha total indicator rim reading. Bar sag will need to be accounted for during vertical adjustments but will be negligible for horizon adjustments. Figure 42 shows a typical setup for taking rim readings.


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Figure 42: Taking Rim Readings Talk Page

Procedure 1. Zero the dial indicator at the 12 o'clock position (3 o'clock position for horizontal moves).

2. Rotate the indicator 180 and read the error from the difference in reading. This is the TIR. 3. Calculate proper shim movement by dividing the TIR by two; this will be the shim adjustment for all four feet.

Example 2:Rim and Face Parallel Misalignment Calculation Given the following information from Figure 43, calculate the requ shim moves to achieve perfect angular alignment. Rim Reading @ 12 o'clock: .000 Rim Reading @ 6 o'clock: +.038 Bar Sag: .010

Figure 43: Example Two

Solution: Perfect parallel offset alignment may be achieved by adding .024 inch shims under each foot of the movable mach Negative numbers indicate shims to be removed, while positive numbers indicate shim addition. Talk Page


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Cross Dial

Cross dial alignment is another method of achieving the same results as the rim and face method. Although it is not any more accurate, it is a much faster method of alignment. The reason for this is that both angular and parallel misalignment can both corrected for at the same time. The shafts must be able to rotate together to perform this alignment, which will make it a bet choice if you are shutting down a piece of equipment to check the alignment. The solutions for cross dial may be calculated mathematically or graphed out. Figure 44 shows a typical dial indicator setup for the cross dial alignment method.

Figure 44: Typical Dial Indicator Setup for Cross Dial Alignment

Talk Page

Mathematical Solution The mathematical formula for doing a cross dial alignment follows a basic riseoverrun geometric principle. By following this principle, the alignment of machinery can be easily accomplished using the following formulas:


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where: A=Distace Between Dial Indicators B=Distance from Stationary Machine Indicator and Front Foot C=Distance from Stationary Machine Indicator and Rear Foot SM=Sationary Machine Indicator Reading MM=Movable Machine Indicator Reading

For ease of use, this formula is incorporated into a shaft alignment data form, shown in Figure 45. This is a fillintheblank representation of the preceding formula. By filling in the appropriate information into the proper boxes, the calculation of the required shim changes for correcting both the angular and offset misalignments can be determined. The steps to completing form are as follows:

1. Enter the total indicator reading (TIR) for the stationary machine (SM) and the movable machine (MM) indicators in the labeled ASM TIR and AMM TIR . Ensure bar sag has been accounted for. 2. Enter distance between SM and MM indicators in the block labeled AA . 3. Enter distancebetween SM indicator and the MM front foot in the block labeled AB . 4. Enter distance between SM indicator and the MM rear foot in the block labeled AC . 5. Enter previously recorded data in the calculation area of the form and calculate the MM front and rear foot moves.

Figure 45: Shaft Alignment Form Example 3:Cross Dial Mathematical Misalignment Calculation

Given the following information, calculate the required shim moves to achieve perfect parallel and angular alignment. Assume the MM dial starts in the 12 o'clock position and the SM dial starts in the 6 o'clock position. SM Indicator TIR = +.030 MM Indicator TIR = .026 Bar Sag = .006 AA Dimension = 6 AB Dimension = 14


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https://www.myodesie.com/index.php/wiki/index/returnEntry/id/2955 AC Dimension = 32

Solution: You may notice that the SM and MM TIRs are different from the given. This is because bar sag must be accoun for. In this example, .006 inch must be added to the MM TIR, and .006 inch must be subtracted from the SM TIR for corre calculations, which makes the SM TIR+.024 inch and the MM TIR .020 inch.

Figure 46 shows the calculation using the cross dial alignment form. When using this form, you may find it convenient to mils instead of thousandths of an inch. This allows the use of whole numbers and avoids confusing decimals. For examp the TIR was .027 inch, you would enter 27 on the form. When using mils, remember the solution will also be in mils; that is, would actually be+.0325 inch. The example in Figure 46 uses mils and the same given data as above.

Figure 46: Calculation of Example Three Using Cross Dial Alignment Form Talk Page

Graphical Solution The graphical solution for cross dial alignment problems is a method that will give you an actual visual indication of the misalignment. The results will be the same as if it were calculated mathematically though. Talk Page

Procedure

1. Lay out a horizontal line at the approximate middle of the graph paper. This is the running alignment line (RAL). 2. Lay out a vertical line near the left edge of the graph paper. This represents the SM dial indicator position. 3. Lay out another vertical line scaled from the SM indicator line that represents the MM indicator. If the distance is 6" and are using a 1:1 scale, the line will be six blocks from the SM indicator line. 4. Lay out another vertical line scaled from the SM indicator line that represents the MM front foot. 5. Lay out the last vertical line scaled from the SM indicator line that represents the MM rear foot. 6. Determine the SM dial indicator TIR (remembering to account for bar sag) and divide the reading by two. This is your pl point on the SM indicator line. Positive readings are above the RAL, and negative readings are below the RAL. 7. Determine the MM dial indicator TIR (remembering to account for bar sag) and divide the reading by two. This is your p point on the MM indicator line. 8. Using a straight edge, extrapolate these plotted points across the vertical lines for the MM front and rear foot. This is the misalignment line. 9. On the vertical lines for the MM feet, count the number of blocks either up or down from the misalignment line to the RA the misalignment line is above the RAL, shims must be removed. If the misalignment line is below the RAL, shims must be added. Assuming a 1:1 scale is being used, each block equals .001 inch.

In the next example, we will use the same dimensional data and indicator readings as used in cross dial Example 3. This will le


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https://www.myodesie.com/index.php/wiki/index/returnEntry/id/2955 compare the two methods. Example 4:Cross Dial Graphical Misalignment Calculation

Given the following information, calculate the required shim moves to achieve perfect parallel and angular alignment. Assum MM dial starts in the 12 o'clock position and the SM dial starts in the 6 o'clock position. SM Indicator TIR = +.030 MM Indicator TIR = .026 Bar Sag = .006 AA Dimension = 6 AB Dimension = 14 AC Dimension = 32 Solution:

When comparing the graph in Figure 47 to the mathematical solution from Example 3, you can see that the results are very si Accuracy is very dependent on the scale chosen for the graph. Remember: the neater and more precise the graph, the mo precise your solution will be. Results will also become more accurate as the movable machine becomes nearer to the RAL. Whenever possible, you should use a vertical scale of one block equals .001" or, even better, one block equals .0005" (space permitting).

Figure 47: Graph for Example Four Talk Page

Reverse Dial

Reverse dial alignment is very similar to cross dial both in theory and misalignment calculation. They both can either be calcu mathematically or graphically. Although there are slight differences in the formula and the plotting, the process is practically same. The two major advantages to using reverse dial over cross dial are that many premanufactured rigs are set up for reve dial, and you may achieve alignment with only three points. Although a cross dial alignment only requires three points to read still need the space for the indicator setup, whereas the reverse dial setup, with both indicators in the same plane, allows alig of machines that are spacelimited. By zeroing the indicator at the 12 o'clock position and reading the 3 and 9 o'clock positio the 6 o'clock position may be determined. The characteristics of a circle tell us that the sum of the side readings, when read w dial indicator, must equal the sum of the top and bottom readings. This is shown in Figure 48.


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Figure 48: Unknown Position Using a Circle The ability to only read the shaft a three points can be a major advantage, but there are some flaws to using this method all time. In order for this to work, you must read at exactly the 12, 3, and 9 o'clock positions. Generally, this can lead to some inaccuracies when calculating the 6 o'clock position. One way of ensuring the readings are taken at the correct points is to u combination bubble level attached to the shaft. When the bubble is exactly in the center, you will be at the correct position read the indicator. This is sometimes called a fourpoint indicator. Figure 49 shows a typical reverse dial setup.

Figure 49: Typical Reverse Dial Setup Talk Page

Mathematical Solutions

For ease of use, the reverse dial formula has been incorporated into a shaft alignment data form, shown in Figure 50. By filling appropriate information into the proper boxes, the required shim changes for correcting both the angular and offset misalign can be determined. The steps to completing this form are as follows.

1. Enter the total indicator reading (TIR) for the stationary machine (SM) and the movable machine (MM) indicators in the labeled ASM TIR and AMM TIR . Ensure bar sag has been accounted for. 2. Enter distance between SM and MM indicators in the block labeled AA . 3. Enter distance between SM indicator and the MM front foot in the block labeled AB . 4. Enter distance between SM indicator and the MM rear foot in the block labeled AC . 5. Enter previously recorded data in the calculation area of the form and calculate the MM front and rear foot moves.

Figure 50: Reverse Dial Shaft Alignment Form

Example 5:Reverse Dial Mathematical Misalignment Calculation Given the following information, calculate the required moves to achieve perfect parallel and angular alignment.


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https://www.myodesie.com/index.php/wiki/index/returnEntry/id/2955 SM Indicator TIR = .024 MM Indicator TIR = .010 Bar Sag = .006 AA Dimension = 5 AB Dimension = 8.5 AC Dimension = 14

Solution:Figure 52 shows the calculation using the reverse dial alignment form. When using this form, you may find it convenient to use mils instead of thousandths of an inch. This allows the use of whole numbers and avoids confusing decimals. For example, if the TIR was .027 inch, you would enter 27 on the form. When using mils, remember the solution also be in mils; that is,+32.5 would actually be+.0325 inch. The example in Figure 52 uses mils and the same given data a above.

You may notice that the SM and MM TIRs are different from the given. This is because bar sag must be accounted for. In example, .006 inch must be added to the TIRs for correct calculations, which makes the SM TIR+.030 inch and the MM T inch. Note: This alignment form applies to and should be used for the reverse dial method of alignment only.

Figure 52: Calculation Using Reverse Dial Alignment Form Talk Page

Graphical Solution

The graphical solution for reverse dial alignment problems is a method that will give you an actual visual indication of the misalignment very much like that used for cross dial alignment. The results will be the same as if they were calculated mathematically. The only difference in this type of alignment is that the MM indicator reading must have its sign changed be plotting. Talk Page

Procedure

1. Lay out a horizontal line at the approximate middle of the graph paper. This is the running alignment line (RAL). 2. Lay out a vertical line near the left edge of the graph paper. This represents the SM dial indicator position. 3. Lay out another vertical line scaled from the SM indicator line that represents the MM indicator. If the distance is 6 inche you are using a 1:1 scale, the line will be 6 blocks from the SM indicator line. 4. Lay out another vertical line scaled from the SM indicator line that represents the MM front foot. 5. Lay out the last vertical line scaled from the SM indicator line that represents the MM rear foot. 6. Determine the SM dial indicator TIR (remembering to account for bar sag) and divide the reading by two. This is your pl point on the SM indicator line. Positive readings are above the RAL, and negative readings are below the RAL. 7. Determine the MM dial indicator TIR (remembering to account for bar sag) and divide the reading by two and then ch the sign (positive readings become negative and negative readings become positive). This is your plot point on the MM indicator line. 8. Using a straight edge, extrapolate these plotted points across the vertical lines for the MM front and rear foot. This is the misalignment line. 9. On the vertical lines for the MM feet, count the number of blocks either up or down from the misalignment line to the RA the misalignment line is above the RAL, shims must be removed. If the misalignment line is below the RAL, shims must be added. Assuming a 1:1 scale is being used, each block equals .001 inch.

In the next example, we will use the same dimensional data and indicator readings as used in reverse dial Example 5. This will you compare the two methods.

Example 6:Reverse Dial Graphical Misalignment Calculation Given the following information, calculate the required shim mov achieve perfect parallel and angular alignment. SM Indicator TIR = .024


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https://www.myodesie.com/index.php/wiki/index/returnEntry/id/2955 MM Indicator TIR = .010 Bar Sag = .006 AA Dimension = 5 AB Dimension = 8.5 AC Dimension = 14 Solution:

Note: The graph scale for this example is as follows: Horizontal Scale 1 Block = .5 Vertical Scale 1 Block = .001

Figure 53: Reverse Dial Graphical Calculation


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