I have a question about laser alignment. This piece of equiptment, the gearbox shaft, there is not enough shaft length from behind the coupling on the gearbox. if I where to attach the laser to the coupling onthe gearbox, and attach the other laser to the saft of the motor, would I still be able to acheive a good alignment?

Yes, if coupling and shaft have a solid fit, without movement during procedure.

Be sure to check the runout of the coupling hub also.

Danny, he doesn't need to check runout if two shafts are coupled during rotation.
Regards

Of course dial indicators will give the same results and same accuracy if there's enough room for the bracket.

Run-outs should always be checked on first and second members while the third member usually is flexible or movable (first = shaft; second = hub; third = shroud, grid, rubber boot, etc...).

I agree with ivaperez if the coupling has a solid fit with the shaft and the entire assembly is rotated togheter runout should not be a problem

Run-out isn't a problem with dynamic alignmet: but it is with the operation of a machine. Run-out must always be checked and within tolerance else you're aligning the concentric centerlines of the machines when you're actually aligning machine that can't give good service and are out-of-tolerance. Alignment won't correct run-outs!

I ran into a problem not long ago that I suspected severe misalignment. The alignment was checked and looked well within tolerance. So I had them break the coupling and checked runout with an indicator and found .023 runout on the chiller shaft. I even posted a thread on it here and asked if an alignment check should have caught the bent shaft. The answer was that you can align a something with a bent shaft and not catch it with alignment and I had the proof to support it.
One question does come to mind though, if both shafts were running true and the coupling hub where the alignment rig is attached has runout, wouldn't you be able to align it under these conditions?
Ronnie

Using dynamic methods aligns the concentric centerlines of the shafts; not the coupling. So you're aligning an imaginary line that is perfect, running through the center of the bearings. You can easily prove this. Run-out is incorporated into your reading if you have one shaft stationary. If your shaft is bent 0.125" and the dynamic method is employed the dial indicators or laser won't see it. Run-out checks must always be made.

Sam is right on the money! A good alignment JOB goes well beyond just making laser or dial indicator measurements.
My associate once made a quick, but accurate, laser alignment only to find that the vibration was higher afterwards. The coupling was not inspected, because the laser works with both shafts coupled. He later found that the Woods-type coupling insert had taken a distorted shape from the severe misalignment and was now "uncomfortable" with the shafts aligned.
Doing it right the first time certainly applies to alignment jobs!

Walt

Good Question.

First, by rotating both shafts together you are actually performing a rotational centerline alignment, not a coupling alignment. Runout of the couplings will not matter for these measurements. Even with the coupling disassembled, if both shafts are indexed at 9, 12 and 3 together the alignment data will come out fine...assuming all of the prealignment considerations are followed. This includes making sure the mounting fixtures are solid, ect.

As far as the coupling having runout or the shaft being bent...this is not an alignment issue. I highly recommend measuring and correcting any problems you find. This will most likely show up as an unbalance (depending on speed and severity of the runout) or perhaps some gear train problems inside the gearbox, again depending on speed and load and severity of the runout. By all means...check the runout...but the shaft alignment results will be independant of ANY runout as long as the shafts are rotated or indexed together.

Best Regards,

Rich Henry

A bent shaft is an alignment issue; no if and's or buts. Are you going to align a bent shaft of 0.056"? NO! You must first check to see if you have alignable machines or waste your time as the client shouldn't pay you if you align something that grossly out of alignment and unalignable.

I just want to say, I appreciate all your replies and input. I was hopeing that I would have some update info of what was found, but due to a change in the schedual, this machine won't be down for a couple more weeks. The piece of equiptment is useing a safety clutch ie ROBA-lastic-highly flexible Type 131 and the repaired motor was installed on a different shift. I spoke with the people involved with the install of the motor and was told that they did use dial indicators and the alignment was "as good as they could get it". After the machine was running under load, you could feel a vibration from the motor, or the coooling fan on top of motor. Our vibration tech later flagged as a alignment problem. I believe he said it was moveing approx 11 mils but I did not see the report yet. I did notice that the temp reading of this motor where alot hotter than a alike machine. Again, thanks for all the replies and I'll let you know how the battle goes..

B_1_3_GB_18_10_2004.pdf (88 Kb, 35 downloads) Clutch info

Sam, why is it that we are always butting heads on here...

Sam wrote:
"A bent shaft is an alignment issue; no if and's or buts. Are you going to align a bent shaft of 0.056? NO! You must first check to see if you have alignable machines or waste your time as the client shouldn't pay you if you align something that grossly out of alignment and unalignable."

You know, Sam, I could align a shaft with 0.056" bend in it...it just wouldn't run very well when I was done.

Here is the definition of shaft alignment:
Co-linear centers of rotation of two or more shafts under normal operating conditions.

If you have a different difinition of shaft alignment I would sure like to know what it is.

A bent shaft running on bearings will have a center of rotation, by definition.

I'm NOT suggesting that a bent shaft is OK (please re-read my previous post if you didn't see that). I am stating, quite emphatically, that a bent shaft does not mean a system is misaligned. Similarly, a worn coupling with excessive backlash does not mean a system is mislaigned. Motor softfoot does not mean a system is misaligned.

All of the above are machine defeciencies that absolutely need to be corrected for the machine to reach it's mythical L-10 bearing life...but they should not to be characterized as misalignment.

I wouldn't walk up to a fan and immediately start balancing it just because I had a report of high vibration. I would look at the vibration data, perform a visual inspection and properly identify the problem before I hung the first trial weight. Those are pre-balancing consideration.

In the arena of shaft alignment there are pre-alignment consideration that need to be completed before moving to the actual alignment of the machinery...these incude...but are not limited to measuring the coupling hubs and shafts for run-out, radially and axially if possible.

If you would like, I could send you a list of pre-alignment considerations that are generally accepted as correct within the alignment universe.

Xracer...sorry for all the sniping on here...sounds like you have a vertically mounted motor. If it has a "rabbit" fit it probably does have some misalignment. In my experience the fit allows for proper offset alignment OR proper angular alignment, but very rarely both. You may have a combination of problems, some misalignment on the DE of the motor and some unbalance on the motor itself.

If you have access to the cooling fan and if it is not made of plastic...you may be able to balance the motor to lower the vibration. Keep in mind that the taller the motor the more "allowable" the unbalance as the greater the distance, the more flexibility in the system. Sort of like balancing a fan mounted on spring isolators. The system is less stiff so a small unbalance will have a larger effect on the system. My personal feelings are to balance it, balance it, balance it...after, of course...completing the pre-balancing considerations.

Best Regards,

Rich Henry

By the way...thanks for posting the specs on the coupling. Those alignment numbers are HUGE. A maximum of 2.5 mm (+/- .100") offset and 3 degrees of angularity (approx .052"/inch).

Stevie Wonder could align a machine to those specs.

Best Regards,

Rich Henry

Rich
I have to agree with you. When I'm called to "align" a piece of equipment I always ask if they want me to check for "soft foot" or run out when I do the alignment. Normally the customer says their guys will do that (which I know they won't), so I just align the rotating centers. I'm reminded of a time I was called in to balance a hammer mill and first balance run showed no balance problem - did a couple of more checks and told them it was misaligned not out of balance. They said "We have to take it out at least once a year for bearings and we know it isn't misaligned because we always put it back the same way." As I stood there trying to figure a way to respond with some level of tact, I was told "If you aren't going to balance it you might as well pack up and leave." So I left. The customer wants what he wants.

Not sure if this is up for vote.. but seems to becoming a hot topic

Maybe a vote is in order ?

I'm in with Rich and Mike,

Is runout an alignment problem?
my 2 cents
A bent shaft is NOT an alignment issue.

support for my 2 cents
No alignment procedure can repair a bent shaft.

Runout is runout, eccentricity is eccentricity, Alignment is Alignment.

Check for runout and eccentricity issues, correct these first, then align correcting softfoot first and
remembering GaryB, make sure thermal growth is taken into consideration.

Mike

Mike,

I don't mean to sound uneducated in the alignment world...but who is Gary B.?

Thermal growth is actually one of my specialties and I have a patent pending set of fixtures for measuring that very thing. OL2R marketed by Fixturlaser Globally and VibrAlign here in the US.

I just completed measurements on two 4 machine trains at a power plant in Iowa. This is the third trip measuring the same machinery...data repeated over 3 separate set-ups (2 offline to NOP/NOT and 1 NOP/NOT to ambient) to less than 2 mils offset and less than 0.2 mils/in angularity. I did all the measurements at the same time...total set up time for the fixtures was less than 4 hours (6 sets of fixtures). The machines were even run with the guards in place...

The data is very easy to get, relatively inexpensive and potentially worth hundreds of thousands of dollars in lost productivity.

I am very aware of the systems available from laser based to water cooled stands and prox probes to Essenger bars.

I agree with your statement about thermal growth...but as it turns out..."that ain't the half of it"...so to speak.

Machines like generators, compressors and large reciprocating engine driven equipment have a tremendous amount of horizontal movement caused by rotor torque among other things. The total dynamic movement picture needs to be accounted for in the "world class" alignment arena. If a machine is critical enough to set the thermal growth values (based on OEM, TLC or Hot Alignment Checks)...it's critical enough to measure everything and set the horizontal and vertical alignments to zero at normal operating conditions.

Best Regards,

Rich Henry

I would think that alignment means that the axis of rotation and the axis defined by the supports are in the ideal positions – compromised however is appropriate for gravity sag or thermal offset.

Whether one considers bent shafts an alignment issue or not depending upon ones accepted definition, bent shafts should be discovered during alignment activities as should soft foot conditions. So whether or not one considers bent shafts an alignment issue discovering bent shafts should be part of the alignment job.

I think William makes a very good point. It sounds like everybody agrees that an alignment can be done with or without shaft runout. But if you align something with a bent shaft, you still have a not so satisfactory job not so well done. So why not make runout and soft foot checks a part of the alignment procedure? Regardless of what we call it, I like it when a job gets done right, the first time. And from what I have read, Most if not all of you feel the same way.

Sincerely,
Ronnie