Laser Alignment Tools: An Overview

How shaft and sheave alignment tools work

Jonathan Trout, Noria Corporation

Laser alignment tools come in user-friendly kits to help you correct multiple types of misalignment. Below we'll discuss how to use a shaft and belt laser alignment tool and more.

Laser Alignment Tools  

The Importance of Laser Alignment

It's estimated that 50 to 70 percent of vibration issues in rotating machinery are caused by misalignment, according to Texas A&M's OAKTrust study on coupling misalignment forces. In fact, reliability equipment supplier VibrAlign reported that one of its customers found that just over half of their plant's machinery was misaligned to some degree. So, why is shaft alignment a big deal?

While misalignment has no quantifiable effect on motor efficiency, correct alignment does ensure you have a smooth and efficient transmission of power from the motor to the driven equipment, according to research on motor shaft misalignment by the University of Tennessee's Maintenance and Reliability Center (MRC). Misalignment creates excessive vibration and high loads on bearings, mechanical seals, packing and couplings, impacting the operating life of rotating equipment. Other effects of misalignment are:

  • Lost production
  • More frequent repair orders
  • Increase in spare parts purchases
  • Low-quality products

Modern laser alignment tools check for three types of misalignment: parallel (offset), angular and a combination of the two. Both of the two main types (parallel and angular) can occur in vertical and horizontal planes.

  1. Parallel (offset) misalignment occurs when the centerlines of the two shafts are parallel but not in the same line. Shafts may be offset horizontally, meaning they're offset to the left or right; or offset vertically, meaning they're positioned at different heights.
  2. Angular misalignment occurs when the motor is offset at an angle in relation to the driven equipment. For example, if you were to draw an imaginary line from the centerline of the motor shaft and the centerline of the driven equipment shaft, the two lines would eventually cross rather than run along a common centerline. Angular misalignment can be horizontally or vertically misaligned. This type of misalignment can cause measurable damage to both the motor and driven equipment shafts over time.
  3. Combination misalignment is a combination of misalignment types that occurs when the motor shaft incurs both angular and parallel misalignment.

Below we'll take a look at how modern laser alignment tools work, the basics of setting up a laser alignment tool and steps to take before aligning your equipment.

 

How Laser Alignment Tools Work

The goal of a laser alignment tool is to ensure the two coupled shafts are aligned; that is, their center lines have a common axis (coaxial). Modern laser alignment tools have a big advantage over traditional alignment tools like a straight edge, optics and dial indicators. They consist of two sensors (a laser emitter and a receiver), brackets, rods, chains and a display unit. Let's break down the different components of a laser alignment tool.

  • Laser alignment sensors: The sensors should be mounted on the shaft, coupling hub, flywheel or brake disc. You'll attach the stationary sensor (normally labeled "S") to the stationary machine and the movable sensor (normally labeled "M") to the movable machine.
  • Brackets: The brackets mount the sensors to the machine. They come in multiple designs and various mounting options like magnetic and non-magnetic V-brackets, offset brackets and V-brackets with sliding wheels for non-rotating shafts.
  • Extension chains: Extension chains help secure the sensors to the shaft and can be adjusted as needed for shafts that are larger in diameter.
  • Extension rods: Extension rods are used to align shafts with large couplings, so laser paths remain unobstructed. Sensors slide directly onto the rods.
  • Display unit: The display unit shows alignment data in real time as the laser alignment tool takes readings. Most display units have built-in software, LCD screens, rechargeable batteries, memory storage, wireless connectivity and more. Many laser alignment tools come with mobile apps that connect to the tool using Bluetooth and display data in real time on mobile devices.
Alignment kit

When it comes to mounting the sensors, six things matter to obtain an accurate reading: measurement methods, distance, angular relationship (inclinometers), bracket assemblies, mounting location and miscellaneous looseness. Let's discuss a few in more detail.

  • Measurement methods include the Express method, the Tripoint method and the Clock method. Modern laser alignment tools come with inclinometers built into the sensors, making the first two methods the best options. In the Express method, alignment is calculated by recording three points while rotating the shafts at least 60 degrees. Once you record the first point, the other two points are automatically recorded when the shaft is rotated to a new position and is held there for more than two seconds.

    The Tripoint method calculates the alignment condition by taking measurements at three points while rotating the shaft at least 60 degrees. Unlike the Express method, measurements are taken manually rather than automatically.

    The Clock method is more of a dated method and involves taking three measurements at the 9, 12 and 3 o'clock points. The clock method is useful when a machine base is not truly horizontal or vertical, such as when mounted at an angle. It's also useful when a horizontal machine is mounted on a vertical plane.

    Newer technology, such as Pruftechnik's sensALIGN technology, now provides users with thousands of measurement points. This multi-point feature takes hundreds of points at any degree; a continous (SWEEP) mode automatically collects those points.

  • Mounting distance is highly adjustable, ranging from the sensors nearly touching to around 35 feet (10 meters) apart.
  • Angular relationship refers to the ability of taking multiple measurements around the shaft. Most modern laser alignment tools have inclinometers built into the sensors. Inclinometers measure the radial position of the sensors. Inclinometer values are used in the calculation of misalignment. This lets you take measurements at any position around the shaft. Inclinometer values are shown on your display.
 

Setting up a Laser Alignment Tool

When you purchase a laser alignment tool, it generally comes in a case with all the components you'll need, such as the display, extension rods, chains, sensors, brackets and user guide. Tool setup varies depending on the brand, type and model you purchase, but most brands are very user friendly. Pre-installed software typically guides you through the steps or setup process for shaft alignment.

Shaft Laser Alignment Tool

  1. First, you should mount your brackets on the coupling. Use the chains to secure the brackets to the shaft, adjusting for the diameter.
  2. Shaft alignment tool
  3. Next, place your sensors on the brackets. Make sure the correct sensor is mounted on the correct side. Sensors will have some way of denoting the appropriate side. For example, an "M" sensor should go on the motor side, while the "S" sensor should be mounted on the stationary side. Once on the correct side, tighten the sensors onto the rods.
  4. Once you've mounted the sensors, you can turn on each one and verify that they are aligned. Modern laser alignment tools are very user friendly and perform nearly all the work for you with built-in software. When setting a new alignment, the software walks you through what to do, starting with getting a few measurements. You'll need to measure from the "S" unit bracket to the center of the coupling, from the center of the coupling to the center of the "M" unit bracket, the horizontal distance from the center of the "M" unit bracket to the first bolt on the motor, and the horizontal distance from the front bolt on the motor to the back bolt. All of these measurements will be plugged into the software.
  5. Next, you'll be asked to enter the machine's tolerances. You can determine these by using the machine and coupling type or by looking at the speed of your machine's motor and comparing it to a pre-loaded or pre-installed tolerances chart. Match the speed of the motor to the corresponding tolerance. Most modern laser alignment tool software comes with a tolerance chart for reference. Below is an example of a shaft alignment tolerances table for direct-couple shafts.
  6. Shaft Alignment Tolerances for Direct-couple Shafts
    Motor Speed
    (RPM)
    Parallel Offset (mils)
    Short-Flex Couplings
    Angular Misalignment (mils)
    Spacer Couplings
    900 3.0 (E), 6.0 (A) 1.2 (E), 2.0 (A)
    1,200 2.5 (E), 4.0 (A) 0.9 (E), 1.5 (A)
    1,800 2.0 (E), 3.0 (A) 0.6 (E), 1.0 (A)
    3,600 1.0 (E), 1.5 (A) 0.3 (E), 0.5 (A)
    *E = Excellent, A = Acceptable. Source: Alan Luedeking, Ludeca, Inc. "Shaft versus Foot Alignment Tolerances: A Critique of the Various Approaches." Via U.S. Department of Energy

  7. After these numbers are entered, it's time to perform vertical correction of the motor. Checking for what is known as soft foot is a key part of this step. This is done using the provided shims and placing them under the "feet" of the motor. A soft foot check can be done in the pre-alignment phase, which we'll discuss later, or after you've taken measurements if you are showing misalignment.
  8. Now, you can connect your sensors to the display using a Bluetooth or wireless connection. This allows you to see real-time data as the sensors work. It also shows you if you need to adjust the sensors. If the angle difference is more than 2 degrees, you should adjust one sensor manually to correct it. Tighten the "M" sensor on the rods and adjust the position of the "S" sensor on the rods until the laser is aligned with the centerline of the "M" sensor. You'll then adjust the "M" unit laser line to match the centerline of the "S" sensor.

Once setup is complete, you cannot make adjustments to the sensors or you'll get inaccurate readings. Upon setup, many laser alignment tool displays show you a 3D view of your machine as it takes the three readings while you adjust to the proper positions (9, 12 and 3 o'clock). The user friendliness of most laser alignment software indicates that you've taken an accurate reading at each position. For example, once the sensors are properly in the 9 o'clock position, a button will go from red to green, allowing you to record that measurement.

Single vs. Dual Laser Alignment

Probably the most common type of laser alignment tool on the market, dual laser alignment tools require you to adjust both lasers so they hit the opposite detector. This usually takes more time, requiring a pre-alignment period. Single laser alignment tools, as the name suggests, requires aligning one laser and is sometimes preferred because the distance between the spacer shaft or the distance between the machines doesn't usually affect the measurment. There's also no need for pre-alignment with single laser alignment tools.

Uncoupled Shaft Alignment

Even though it's quicker and more accurate to align the shaft while the machines are coupled together, sometimes the coupling might need be separated. This might present itself when misalignment causes shaft deflection or bending, when the flexible coupling becomes stiff or when the long shafts protruding from the inboard bearing isn't rigid. To help with uncoupled shaft alignment, some laser alignment tools have built-in inclinometers in the sensors. Others have their own patented technology specific to uncoupled shaft alignment.

Belt/Sheave Alignment Tool

Belt alignment tools, or technically sheave alignment tools, are used to properly align the centerlines of sheave grooves (what the belt runs on) to the proper radial and axial alignment. Because belts are relatively inexpensive, belt or sheave alignment isn't typically considered a major issue; however, misalignment in sheaves can cause other problems in addition to reduced belt life. These problems include:

  • Increased shaft and bearing loading
  • Increased wear of the sheaves leading to reduced sheave life
  • Increased noise and vibration due to belt wear

Belt or sheave alignment tools help detect three types of misalignment: radial runout of the shaft, radial runout of the sheave and axial runout of the sheave. Radial shaft runout usually means the shaft is bent. If it is bent out of tolerance, the shaft should be replaced.

Belt alignment tool

Once you've confirmed there is no radial runout of the shaft, check for radial sheave runout. If runout is noticed, it's usually due to an abnormally bored sheave or bushing. You should replace the sheave before aligning if this is the case.

Axial sheave runout typically means you should check the taper-lock bushing to ensure it is mounted correctly and tightened. It could also mean the shaft is undersized or that the sheave or bushing is bored abnormally.

Belt or sheave alignment tools vary depending on the brand and type, but generally work by attaching two magnetic V-sensors into the grooves of the sheave. Unlike shaft alignment tools, with these tools you only have two components: a laser-emitting sensor and a receiver unit. The receiving unit uses a 3D target area to detect horizontal, vertical and/or parallel misalignment.

 

Pre-alignment Steps to Take Before Using a Laser Alignment Tool

Performing accurate alignment starts before you even set up your laser alignment tool. These pre-alignment steps and checks are suggested by VibrAlign to ensure your laser alignment tools work properly and accurate alignment is achieved.

  • Preparation: Preparation involves inspecting the machine you intend to align. This includes examining the coupling's insert and lubrication; checking for loose bolting, most notably the feet of the machine; and inspecting for obvious pipe strain.
  • Rough in shafts using a straight edge: This process involves positioning the centerline of the movable shaft with the centerline of the stationary shaft, both horizontally and vertically. This helps save time when you're setting up your alignment tool later and increases the accuracy of the laser shaft alignment process. You should rough in to around 20 mils.
  • Correct soft foot: Have you ever been to a restaurant, sat down, put your arms on the table and then felt the table jerk suddenly to one side, nearly spilling your water? That is soft foot. Soft foot as it pertains to shaft alignment refers to the down bolts holding the movable machine in place. To check for soft foot, start by trying to insert a 5-mil shim under three corners of each foot. If it fits, go up to the next thicker shim until the gap under the foot is minimized. You can also use a dial indicator to see how much vertical movement the foot has and shimming until movement is minimized. Do this process for each foot.
  • Tighten feet in a diagonal pattern: To help minimize any remaining soft foot, tighten the feet in a crisscross pattern every time the feet have been loosened or tightened.
  • Check for final soft foot: Loosen one foot of the movable machine and check for any remaining soft foot by using the methods mentioned above. Check each foot one by one, correcting for any remaining movement.
 

Laser Alignment Tool Pricing

Proper coupling alignment can save you from a variety of problems, such as excessive wear and energy consumption, accelerated shaft and coupling failure, and increased vibration. Maintaining alignment requires regular monitoring. Modern laser alignment tools and their accompanying software have made it quite simple to accomplish this.

So, how much do the tools cost? Price depends on the type of alignment tool (shaft or belt alignment), what's included in the alignment kit and how advanced the tool's features are. For example, a more versatile laser alignment tool with ultra-compact measuring units for very narrow spaces might cost a little more than a standard model. By checking a few major distributor's websites, you can find current pricing for shaft and belt laser alignment tools, such as the following guidelines:

  • Shaft laser alignment tool price range: around $3,700 to $25,000
  • Belt/sheave laser alignment tool price range: around $1,200 to $3,500

Properly aligned machines offer improved uptime and a reduction in maintenance costs. Checking for and correcting misalignment is a fairly straightforward process with the help of modern laser alignment tools.

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