Differences Between A Feeler Gage and Laser/Optical Alignment

As a maintenance manager, machinery operator, or vessel captain/chief engineer, ensuring your machinery operates efficiently and effectively is a top priority. One way to achieve this is through regular alignment checks. Proper alignment not only increases machinery life, but also reduces fuel/energy costs, and minimizes unscheduled downtime. In this blog post, we will discuss different types of alignment; specifically, differences between the most widely used methods: feeler gage, laser, and optical alignment.

Alignment is the process of ensuring each machine is correctly positioned and oriented in relation to their respective components and is done by measuring the theoretical shaft centerlines and moving them to be colinear with each other. The five primary alignment parameters are vertical offset, vertical angularity, horizontal offset, horizontal angularity, and axial offset. Axial offset is most important when a flexible coupling is in the mix as these will have specific “Axial Control Distances” based on manufacturer’s engineering calculations.

The feeler gage alignment method uses a set of flat, precision machined, thin metal strips to collect measurement data. When using this method, the technician places a gage between the coupling flanges at four equidistant points in the coupling: top, bottom, left, and right. Measurements are then recorded and compared – Top versus bottom to assess vertical angularity; left and right to evaluate horizontal angularity. The general rule-of-thumb is that these numbers should vary no more than 0.003” from their counterpart. While this is a quick and easy check, feeler gage alignment will only provide two of the five primary parameters of alignment – vertical and horizontal angularity. It has no way of identifying any vertical, horizontal, or axial offset misalignment.

Optical alignment method uses a precision alignment telescope and machined wire-targets fit to the bores of a shaft line. A reference line is established by “zeroing” the scope at two pre-determined points in the driveline being measured, and the telescopes zooming features allows the technician to evaluate the alignment of each component to the established reference line. This is particularly useful on vessels with the propeller shafts removed. It is important to note that if this method is to be used, a hull deflection measurement MUST be performed to ensure the hull retains its waterborne shape and allows for a true representation of the machinery position under normal operating conditions. While this method is slightly more complicated than the feeler gage method, it will also provide four of the five primary parameters of alignment: Vertical and horizontal angularity as well as vertical and horizontal offset misalignment.

Laser alignment technologies use high-precision lasers and complex internal optics to measure the theoretical shaft centerlines of machinery to be aligned. By entering distances between center of coupling to the receiver, center of coupling to the drive end feet, and drive end to non-drive end feet, the laser alignment system can calculate corrective adjustments to be made based on where the two shaft centerlines are in reference to each other. All laser alignment systems have the ability to measure vertical and horizontal angularity as well as vertical and horizontal offset misalignment parameters; however, some have the ability to measure axial offset by monitoring the return intensity of laser density from laser emitter to its respective receiver.

In contrast to the feeler gage alignment process, optical alignment uses precision instrumentation, and laser alignment uses computers to calculate the final alignment results. Optical and laser methodologies provide more precise and real-time results, making it a superior choice where accuracy is critical to machine performance.

Feeler gage, optical, and laser alignment all offer distinct advantages, depending on the equipment and nature of your application. Feeler gage alignment is a relatively simple and inexpensive way to assess machinery alignment but it only measures angularity. In contrast, optical alignment provides more accurate and detailed measurements for angularity and offset; this is more complicated and requires a technician with specialized training. Laser alignment is by far the most accurate and detailed alignment method, it provides recorded data and is less prone to human error; however, it also requires expensive equipment and specialized training to operate properly. As a maintenance manager, machinery operator, or vessel captain/chief engineer, choosing the correct method for your needs is crucial to ensure optimal performance of your machinery. Regular alignment checks are essential in preventing downtime, reducing vibration, and lowering fuel/energy costs. Ultimately, the type of alignment method you choose should depend on the equipment and application at hand to avoid costly mistakes.

Not sure which method suits your application best? Call AME and speak with an expert for guidance!