June 29, 2020
Common Shaft Alignment FAQ
By Stan Riddle
We get asked a multitude of questions in our training classes, which we appreciate. But a few questions pop up almost every time. Here are some of our most common questions and answers.
QUESTION: Sometimes on small machines, I don’t have enough room on the shaft to mount the laser. Can I mount it on the coupling hub instead?
ANSWER: Yes. As opposed to using rim and face measurements on dials, lasers measure the center of each shaft’s rotational centerline, so it doesn’t matter if one or both laser heads are on the shafts or the coupling hubs. As long as the beams are in the target, you can take the measurement. But make sure you are not mounted to the elastomer or the coupling covers.
QUESTION: Should I get the sensors as close to each other as possible?
ANSWER: No. Actually, the more distance between the sensors, the more sensitive to small movements they are. But in reality, most laser alignment tools can measure very small movements, so it really doesn’t matter.
QUESTION: When aligning a spacer shaft, do I input the middle of the spacer shaft as the center of the coupling?
ANSWER: No. With the Fixturlaser NXA Professional, you can input each coupling center. The result will give you the angularity at each coupling. This is best when you need to know the alignment tolerance for each one. But if your laser doesn’t have a spacer shaft function, you can still achieve a good alignment. Instead of making the center of the spacer shaft the center measurement, choose one coupling or the other, and keep your angularity small.
QUESTION: The numbers on the screen-are they inches, or thousandths, or what?
ANSWER: They are mils. 1 mil=0.001” inches. Displaying in mils means you can show the values without so many character places. As an example:
- -3.5 mil takes 4 characters. -0.0035” takes 8 characters.
Unless you are measuring in metric-then it’s millimeters.
QUESTION: Should I fix soft foot before I start, or last thing?
ANSWER: Yes! Fix it before you begin the process of precision alignment, but always be aware it could come back any time during the alignment process. All it takes is one bad shim, one small piece of grit, or one incorrect shim choice.
QUESTION: This machine has coupling hubs that taper from front to back. Will that affect the laser?
ANSWER: No. Just like when mounting one sensor on the hub, as long as the lasers can target each other, they can measure.
QUESTION: You teach that we should use a torquing pattern each time. Which foot is foot #1?
ANSWER: It does not matter, as long as you begin tightening with the SAME one each time. An easy way to remember this is to use a marker and write the numbers on foot bolt heads.
QUESTION: Is it best to check soft foot with the laser, with a dial indicator, or with a feeler gauge?
ANSWER: It’s a bit of a personal choice, but for me, I think using a feeler gauge, or shim, is the most accurate. If a 3 mil shim will go, but a 4 mil shim won’t, you can correct a soft foot within 1 mil. A dial indicator is good, but often the indicator and the wrench need to be in the same place. While using the soft foot program on a laser is a great way to find out if you have a soft foot, it may not give you the exact amount of shim needed, especially if the soft foot is angled. But it is the best way to find out if any residual soft food is going to cause a non-repeatability problem.