There are three shaft alignment procedure or 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/or graphical solutions. There are various tools that are available to help in the process. The first is a simple pocket calculator. With the 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 a simple 10 x 10 piece of graph paper that gives a pictorial representation of the machines and the amount of movement needed to correct the misalignment. The third method is the use of a computer, either a desktop or a special computer designed specifically for the alignment task. We mentioned the computer method only to make you aware of its existence.
The following are the methods of alignment:
1. Rim and Face (Mathematically Only)
2. Cross Dial (Mathematically and Graphically)
3. Reverse Dial (Mathematically and Graphically)
Rim and Face Alignment
The rim and face alignment method is commonly used where space considerations would prevent the use of the cross dial or reverse dial methods. It also is the only method that can be used when rotation of both shafts cannot be accomplished. The results 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.
- Angular Misalignment Corrections: The face dial is used to measure the distance between the coupling faces. This measures the angular misalignment in both the 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 gives the actual difference in distance between the coupling faces. Because of the dial position relative to the face of the coupling, bar sag will not have an effect on face readings. It will still be an issue to consider when taking rim readings though.
- 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.
- Calculate proper shim movement (or horizontal movement) with the following formula:
Gap x Leg Distance
Rim and Face Angular Misalignment Calculation
Given the following information and Figure, calculate the required shim moves to achieve perfect angular alignment.
Face Reading @ 12 o'clock: .000"
Face Reading @ 6 o'clock: -.072
Solution: These calculations tell us that, to achieve perfect angular alignment, it will be necessary to remove 0.216 inches from the front foot and 0.360 inches from the rear foot. Negative numbers will always indicate that shims need to be removed, while positive numbers are an indication that shims will need to be added.
Front foot adjustment= -------------------- = -0.216''
Rear foot adjustment= -------------------- = -0.360''
Gap x Leg Distance