August 13, 2012
Shaft Alignment of Small Machines
By Brad Case
The VibrAlign Training Faculty sees a lot different machines during our training classes across the USA. The one statement that we hear repeatedly from mechanics and millwrights is, “I would rather align a 500 HP motor & pump set than a 10 HP one”. We agree!
While small machines are easier to “physically” adjust during a shaft alignment, their small size presents another set of alignment issues. The electric motors are typically lightweight, the mounting feet are a thin stamping, the bases are rather flimsy when compared to larger and heavier machines, and there are no jacking bolts to control the horizontal adjustment.
What does this mean for the aligner? Well, his/her alignment technique will need to be excellent and a “light” touch is also needed while making the live horizontal adjustment. After roughing in, soft foot absolutely needs to be corrected and a cross-pattern bolt tightening sequence with three passes needs to be followed to minimize movement of the motor. This, however, may not be enough.
During an alignment of an 10 HP motor/pump set during a training class the vertical alignment corrected easily, however the horizontal alignment was extremely “sensitive” and would not stay in tolerance when the hold down bolts where tightened. The bolts where checked for cupped washers which where okay.
The problem? – the distance between the motor feet was only 5-1/2”. The slightest movement at the feet caused the horizontal alignment to move out of tolerance at the coupling.
The solution? – move the sub-base! This application has a motor sub-base bolted to the pump base with a bolt spacing of approximately 10-1/2”.
So for this motor alignment we adjusted the Verti-Zontal compound move slightly.
After getting results, the vertical alignment was corrected by shimming the motor feet and re-tighten those hold down bolts. The sub-base bolts were then loosened and the horizontal alignment adjusted and the bolts re-tightened. It took two modified Verti-Zontal adjustments to get the alignment in tolerance. By the way, when making the horizontal adjustment you don’t need to change the feet dimensions, just move the motor the direction indicated until the coupling values are in tolerance!
Pretty cool, huh?
Ya that is cool but there is not always a sub-base.
A couple of ways I overcome that is to use two washers instead of one and use lubrication and do your torq pattern 3to 4 times slowley and even. Also if you snug a little and then brass ram it lighly to position it does not wiggle all over. You do have to make sure you have corrected all soft foot.
Tell Stan Hi
3600RPM Bell and Gossets are the bane of my existence!!
These little guys are the ones that keep us honest!
Another great article Brad!!
love the responses!…i agree with Chris…the bane of my alignment existance…i also agree with Mike…i watch the angle and offset values as i tighten….if i see movement, i go to the next bolt in my sequence and duplicate the torque, etc, etc…sometimes i go around the pattern 6-8 times
I know a guy named James Garrett who has developed a cool little tool called the clamp and move that he uses as a portable jacking bolt system on these “saddle” type bases. I saw it it action and was very impressed. I know his intention is to sell them and it seems like a no-brainer to have in a tool kit, after all alignment isn’t just about precision measuring, you also need a good way to control the horizontal movement.
Thanks for the plug. As you stated, it is a cool litte tool that gets the job done on motors from 7.5HP all the way up to 150HP as tested, on these type saddle bases, which is virtually on all the Bell & Gossett pumps. It comes in a kit with four clamps and a handy carry case.I also have adapters currently being developed for all the other type saddle bases. It makes the job so much easier and quicker, as you know this already, because you have seen it perform in action. I am currently working on a video to demonstrate how it works and hope to reveal it soon.
can to tel me how can i use otptalign smart rs5 device i sent this massage because i haven’t user manual
thank you very much
Ashraf, The Optalign Smart is not a Fixturlaser Product. You will need to contact Pruftechnik for a user manual for the Optalign Smart.
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