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# FIR FIM Swash and Concentricity

05/07/2018 1:44 AM

Hi. Does anyone know how to calculate FIR/FIM of the Swash &Concentricity which taken/measured on 12 equally position?

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Guru

Join Date: May 2007
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#1

### Re: FIR FIM Swash and Concentricity

05/07/2018 2:21 PM

Does this have anything to do with isotropic visco-elasticity?

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#4

### Re: FIR FIM Swash and Concentricity

05/08/2018 3:08 AM

Ah! Only in rheopectic pseudoplastics.

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#2

### Re: FIR FIM Swash and Concentricity

05/07/2018 7:06 PM

This probably doesn't answer your question, but this is the closest that I can find.

FIR (Full Indicated Runout) is measured when a gauge is put on a rotating cylindrical object. As the object rotates, the gauge moves in and out due to two factors: 1) the object is not round, and 2) the object is off-center (not concentric) with the axis of rotation. The Full Indicated Runout or Full Indicated Measurement (FIM) is the sum of these two effects.

The best you can do with 12 measurements, I suspect, is to take the difference between maximum and minimum as the Total Indicated Runout (TIR).

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#3

### Re: FIR FIM Swash and Concentricity

05/08/2018 12:27 AM

GA! But I can't help but notice that the FIM measured on a part that is both off center and not fully round would depend on the angular relationship of the off-center peak with the out-of-round peak or trough. If the off-center peak happens to coincide with the out-of-round trough, the two errors could partially (or even completely, for that angular position) cancel each other.

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#6

### Re: FIR FIM Swash and Concentricity

05/08/2018 9:45 AM

That's a good point. Errors in concentricity and roundness can reinforce or cancel like any harmonically related signals, depending on the phase relationship. The concentricity can be considered the fundamental frequency and roundness errors as fundamental and higher harmonics. Looked at as a signal processing problem, you should probably expect the sum to be the root mean square of the individual components.

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#7

### Re: FIR FIM Swash and Concentricity

05/08/2018 11:38 AM

If we are looking at a shaft coupling we would need a whole lot more measurements and good reference points on each shaft.

For eccentricity I'd fix an indicator to one shaft and indicate the other shaft with the two shafts rotating together. That gives me the offset between axes of rotation.

Then to measure angular misalignment, I'd need a set of readings with an indicator fixed to one shaft against a collar on the second shaft with both shafts rotating together.

Finally, I'd need runout measurements on both shafts using a fixed dial indicator. You would need the runout at a few locations across the coupling joint surface to pick up something like a dent, wear or a bent shaft.

Given all of that, you can put together a fairly good picture of what the joint will end up looking like and what sort of coupling you will need to fabricate. It will also tell you if the equipment needs realignment.

The 12 original readings don't give much of a picture unless you know the conditions under which they were taken. Even if you do know, the picture will be far from complete.

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#8

### Re: FIR FIM Swash and Concentricity

05/08/2018 12:12 PM

"The 12 original readings don't give much of a picture unless you know the conditions under which they were taken. Even if you do know, the picture will be far from complete."

This is especially true, since the OP did not specify which 12 measurements were taken.

For radial measurements, it would be perfectly logical to assume radial distances measured every 30° as the part is rotated.

But since he mentions swash, there must be some axial measurements as well, so possibly one axial and one radial measurement every 60°. Just as radial errors may include offset, off-center, and out-of-round, axial errors may include offset, off-normal, and out-of-flat.

Finally, he mentions concentricity. This could conceivably refer to the agreement (or lack thereof) between the center of a single circular part and its axis, or between the centers of two supposedly coaxial parts.

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#5

### Re: FIR FIM Swash and Concentricity

05/08/2018 3:10 AM

Thanks for the translation. It does save readers going to www.acronymfinder.com to find out WTF the TLAs mean.

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