Hello ,

Basically I am doing an alignment for a Gearbox to compressor. The machine is already centered and aligned to zero (almost). But I have a data sheet from OEM with target values or value I must reach, this requires the machine to be misaligned a bit to compensate for thermal growth . They have give the desired final alignment values in Reverse dial indicator method.

If I can convert the reverse dial values to angle and offset values, I can then insert this as thermal growth values to my laser kit. This feature is available in Fixturlaser NXA,

Could someone please share a method to calculate the desired angle and offser? I would appreciate it if you can share formula or Excel sheet with conversion.

Abdul Rahman

Original Post

This info. is from Optalign Application Note #6 (11/21/1985) for "Misalignment Specifications per Reverse indicator Method":

MTBM (moveable) = A

Stationary = B

Dial-A is mounted on B and indicating on A

Dial-B is mounted on A and indicating on B

View is from A (MTBM) toward B (Stationary)

Vertical parallel offset target = -A vert./2

Horizontal parallel offset target = -B horiz./2

Vertical Angular Gap = (B-vert + A-vert)/2

Horizontal Angular Gap = (B-horiz. + A-horiz.)/2

Note: add SAG value to each vertical value, if specified

It would be wise to check this math by graphical or other method!

Walt

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First off, use some care with the anticipated growth numbers on the gearbox.  Some manufacturers give estimated growth based on a nominal 100° F temperature rise expecting the end user to make appropriate adjustments if for example,  the rise is only 70°.

I've attached a graphic I put together way back in the mid-1970's for my technicians in the test department of a major gear manufacturer.  I later adapted the procedure to an HP-45.   That reduced the error rate considerably as some of my techs were not familiar with algebra.  Hint, be careful of sign (+/-) of the measurements.

You might also review the link at https://oaktrust.library.tamu....ce=1&isAllowed=y.  Also old, but quite good.

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Walt Strong posted:

This info. is from Optalign Application Note #6 (11/21/1985) for "Misalignment Specifications per Reverse indicator Method":

MTBM (moveable) = A

Stationary = B

Dial-A is mounted on B and indicating on A

Dial-B is mounted on A and indicating on B

View is from A (MTBM) toward B (Stationary)

Vertical parallel offset target = -A vert./2

Horizontal parallel offset target = -B horiz./2

Vertical Angular Gap = (B-vert + A-vert)/2

Horizontal Angular Gap = (B-horiz. + A-horiz.)/2

Note: add SAG value to each vertical value, if specified

It would be wise to check this math by graphical or other method!

Walt

Hi Mr. Walt

Thank you for information. I am really grateful for your help and it really helped me with an ongoing job. Is there any formula for the rim and face method also. I am only used to laser alignment systems.

Also, how do I verify the calculation graphically.

Thankfully

Abdul Rahman

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Walt Strong posted:

This info. is from Optalign Application Note #6 (11/21/1985) for "Misalignment Specifications per Reverse indicator Method":

MTBM (moveable) = A

Stationary = B

Dial-A is mounted on B and indicating on A

Dial-B is mounted on A and indicating on B

View is from A (MTBM) toward B (Stationary)

Vertical parallel offset target = -A vert./2

Horizontal parallel offset target = -B horiz./2

Vertical Angular Gap = (B-vert + A-vert)/2

Horizontal Angular Gap = (B-horiz. + A-horiz.)/2

Note: add SAG value to each vertical value, if specified

It would be wise to check this math by graphical or other method!

Walt

Hi Mr. Walt

I did the calculation according to the formula. But values did not match the value given by Fixturlaser device. Should we not include DBSE value in the calculation?

Thanks again!

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The simple formulas above are intended for converting reverse indicator values to thermal offsets, as OP stated. The basic assumption is that the indicator positions are close to the laser system positions. The Vendor should provide the thermal offset (horizontal and vertical) specified at the coupling center. You have a compressor-gearbox-Motor/Turbine, so thermal growth of each component should be known. If you really want to learn and understand shaft alignment, then here are a few references and search links:

Shaft Alignment Handbook (Mechanical Engineering) 3rd Edition

From <https://www.amazon.com/Shaft-A...eering/dp/1574447211>

Search: reverse indicator alignment method

https://www.bing.com/search?q=...Ir9uh9NXtzajjuFvShiF

Machinery Vibration: Alignment

By Victor Wowk

From <https://www.globalspec.com/ref...-6-reverse-indicator>

Search: reverse indicator alignment graphical method

https://www.bing.com/search?q=...440EBFDFF11418EC274A

https://oaktrust.library.tamu....ce=1&isAllowed=y

Walt

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From the first link I provided “...However, when it gets down to the correction in the field, one must get down to hard rock fundamentals. The cold alignment will be done with measuring devices in the field by machinists, technicians, and/or engineers. Several know how to determine the moves. Very few know how to move the machines graciously and accurately! Piotrowski recently said, "People, not lasers and dials, move equipment!".

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"People, not lasers and dials, move equipment!" What a great quote!

What I noticed is that there is a lot of emphasis on the measuring instruments and calculations that is way more than what is given to the feild needs like cleanliness of surfaces, inspection of possible cracks or restrictions, correct way installation of shims etc. The know how in such aspects is extremely essential but unfortunately these aspects are given less attention in the literature.

But that is only my thought and I could be totally wrong as in many cases.

Regards- Ali M. Al-Shurafa

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