ISO Standard- gauge block wringing film- calibration controversy

I noticed a lively discussion (now closed) about whether a wringing film thickness is included in gauge block calibrations. I belive most of the world will agree that ISO Standards are the most used when standards are required, so in this sort of discussion I always look there. I rather quickly found the following:

ISO 3650:1998(en)
Geometrical Product Specifications (GPS) — Length standards — Gauge blocks

https://www.iso.org/obp/ui/#iso:std:iso:3650:ed-2:v1:en

"3.2
length of a gauge block
l
perpendicular distance between any particular point of the measuring face and the planar surface of an auxiliary plate of the same material and surface texture upon which the other measuring face has been wrung
SEE: figure 1
Note 1 to entry: The length of a gauge block, l, includes the effect of one-face wringing (see 8.3.1)."


As I have noted above- stating "chapter and verse" is a very good way to state the facts (as opposed to " read the standard".
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On the other hand, this article;
http://www.metas.ch/metasweb/Fachbereiche/Laenge/Dokumente/2003 SPIE SanDiego GaugeBlocks.pdf

examines the uncertainty of optical calibration Vs. mechanical, saying that optical has the disadvantage of having to wring a block, but mechanical calibration is faster.

It appears that the optical method with a wrung block is the primary standard, but the non-wrung mechanical calibration method is also often used.


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The B89.1.2M-1991 ANSI/ASME standard can be found here:

http://www.resenv.cn/Knowledge/ShowPDF?fileName=US-ASME&docName=ASME B89.1.2M-1991.pdf

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The Elsmar forum (a very good metrology forum BTW) has an interesting note that there is a lot of contradictory info on wringing films (or was back in 1999 when the post was made).

http://elsmar.com/pdf_files/uncertainty/Uncertainty_Threads/Uncertainty-wringing.txt

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The more I look the more I find, so I think I will stop now!
GR

most gage blocks i have used get coolant on them which dries to a thick sticky residue. so most machinist want to clean it off which if a shop towel does not work they might use alcohol.
.
i guess i have worked around too many machinist that do not know what they are doing including myself

For those wondering what kind of measurement range a wrung block thickness might be (emphasis on might!), this NPL report has examples from various experiments done over the years and the standard deviations of film thickness for various block materials:

From NPL report CLM3


http://www.npl.co.uk/publications/m...to-the-variability-in-wringing-film-thickness.

Wringing film thickness;
From -60nm to +17nm (1921- 1927)
Newer experiments;
5 to 10nm (1958)
-17nm (+/-11nm) ( 1982)


Wringing film thickness repeatability:
1 steel block wrung: SD 3nm
1 Carbide block wrung: SD 6nm
1 Ceramic block wrung: SD 9nm
4 gage block stack; SD 24nm

Hi greif1,

Thanks for that detailed research.

Wringing films are real, but their characteristics are not fully understood.

This subject is discussed in some detail in Appendix B of the Gage Block Handbook from NIST.
You can download it from the NIST website: National Institute of Standards and Technology

I think this lack of formal physical definition and modeling is the reason for much of the controversy.

- Leigh

Good grief greif1 - and that's to be taken as a compliment

The real Leigh said:

I think this lack of formal physical definition and modeling is the reason for much of the controversy.

Click to expand...

I think the reason is that research on gage blocks effectively stopped more than three decades ago, back when measurement instrumentation was much less sophisticated than it is today. "The Gauge Block Handbook" has been referred to reverentially more than once in recent threads. Although the date 2005 appears next to it on the NIST site it also says "with corrections," with the document appearing to be the same as originally published in the 1970s. The only two references in it are from 36 and 45 years ago, which makes them practically pre-historic as far as measurement technology goes.

Whatever the nature of the film/interface between two gage blocks that are wrung together, height difference measurements have to be made on a length scale of 10 nm. While optical interferometry was capable of that back in the 1970s, it was (and still is) limited to horizontal resolutions ~25x worse than this (i.e. to half the wavelength of light, which is ~250 nm). Direct mechanical measurements with the necessary horizontal and vertical resolutions are easily made with several forms of scanning probe microscopies. However, they were invented in the 1980s, after research on gage blocks was no longer active.

A paper on the NIST website calls gage blocks "a zombie technology," because it really should be dead by now:

http://emtoolbox.nist.gov/Publications/NISTJResMay-Jun2008-113-3.pdf

As long as people continue to refer to publications that are more than three decades old (even if reprinted more recently), the controversy probably will continue.

opscimc said:

As long as people continue to refer to publications that are more than three decades old (even if reprinted more recently), the controversy probably will continue.

Click to expand...

I suppose we should stop referring to the metre, since it was last defined in 1983 (more than 3 decades ago).

Technology builds on prior achievements and understanding. That's the fundamental nature of science.

- Leigh

The real Leigh said:

Technology builds on prior achievements and understanding. That's the fundamental nature of science.

Click to expand...

Yes, but...

In the case of gage blocks we're talking about technology, not about science. Judging only by the various specifications and standards referred to in these two recent threads it appears very little if any science has been applied to this problem for decades. Either the research funding or the interest by scientists was lacking in questions related to "the gage block interface," resulting in things having been written in some publications that never could have appeared in a reputable scientific journal. If a scientist measured two blocks to each be 1.0" long to within what he thought was an absolute accuracy of 1 nm, but found after wringing they were 10 nm less than the sum of the two lengths, he either would realize he made a mistake with his original (or subsequent) measurements, or he would have to propose some physical explanation for the result. Unless that physical explanation was somehow plausible to the referees (and, I must say, it is very difficult to believe there could be any such plausible physical explanation ), the manuscript quite rightly would be rejected.

The appendix to the NIST handbook dealing with wringing films says:

some wrings will be over 25 nm (1 μin) and some less than 0. (Yes, less than zero.) [B3,B4.B5,B6]

Of those four references, [B6] is the only one in a refereed scientific journal in the past half-century (it dates from 1970). However, that particular paper only addresses the adhesion force and does not claim there is a negative film thickness. So, the reference to "less than zero" must be in one of the other papers.

p.s. the second-newest scientific paper dates from 1956, nearly 60 years ago. If anyone wants to look up this one, there's a typo in the NIST publication. It's in volume 27, not 17, of the J. of Applied Physics. I've only skimmed it so far, but it's clear that measurement technology has come a long, long way since 1956. Again, this paper seems to deal only with the contact force, but in the conclusion they make passing reference to the film thickness saying that whether it's positive or negative, it's certainly less than 10 nm. From the context it doesn't seem they are referring to their own measurements but rather summarizing what others have reported in the context of their own measurements. That is, mentioning it in a way that they could say they hadn't ignored it but without having to actually come down on one side or the other of the question.

opscimc said:

mentioning it in a way that they could say they hadn't ignored it but without having to actually come down on one side or the other of the question.

Click to expand...

I suggest you do your own research and present it to NIST for evaluation.

If they accept it, so will we.

Until then, we'll go with what NIST says.

And to what "question" are you referring? I wasn't aware of any question being discussed.

Your opinions regarding the validity of published information are just that... your opinions, of significance to noone but you..

- Leigh

The real Leigh said:

And to what "question" are you referring? I wasn't aware of any question being discussed.

Click to expand...

Gee, it seems pretty clear to me that there is a question being discussed, and that the question is to what extent the film of oil between two wrung gage blocks contributes to the overall height of the stack. And further, whether that film somehow could have a negative thickness, as the two employees of NIST seemed to believe it could when they wrote that in-house publication.

The real Leigh said:

I suggest you do your own research and present it to NIST for evaluation.
If they accept it, so will we.

Click to expand...

Note that NIST does not classify the "Gauge Block Handbook" as as one of their 'Internal Reports' or one of their 'Technical Notes', nor did it appear as a refereed article in their 'Journal of Research.' So, it's not like NIST "accepted" it as anything more than something a couple of their employees wrote to be helpful.

opscimc said:

Gee, it seems pretty clear to me that there is a question being discussed, and that the question is to what extent the film of oil between two wrung gage blocks contributes to the overall height of the stack.

Click to expand...

As greif1 so kindly quoted from ISO 3650:1998(en):

greif1 said:

INote 1 to entry: The length of a gauge block, l, includes the effect of one-face wringing (see 8.3.1)."

Click to expand...

Are you questioning that statement, quoted from a published international standard?

For clarification, a "wringing film" is comprised of various liquids, not just "oil". One of those specifically mentioned is water.

We do not fully understand the nature and characteristics of wringing films. That does not call their existence into question.

- Leigh

The real Leigh said:

snip

We do not fully understand the nature and characteristics of wringing films. That does not call their existence into question.

- Leigh

Click to expand...

Don't you just love something that can be thinner than nothing? ;-)

Newton pretty much got the big things all described with math and numbers, the atomic physicists are thinking they have the little things boxed up neatly. Mean while, there are those 'tween sized bits still posing a puzzle.

I mean, just what does hold two wrung blocks together ;-) 'taint air pressure!

CalG said:

I mean, just what does hold two wrung blocks together ;-) 'taint air pressure!

Click to expand...

Absolutely true.

Two blocks that are absolutely clinically scientifically clean will not wring.

The common solution to that problem is to rub one face on a finger. It picks up enough skin oil to do the job.

- Leigh

The film is just a part defined by a nominal and given a tolerance.



It exists between 2 surfaces only (why there is only 1 not two per block in the stack).

HM

Doesn't the literature explanation that the film thickness can be a negative value give you a moment's reflection on the subject of tolerance and certainty?

The real Leigh said:

As greif1 so kindly quoted from ISO 3650:1998(en):
...
Are you questioning that statement, quoted from a published international standard?

Click to expand...

What I wrote has nothing to do with that statement. I've reread what I wrote and can't understand how it could be misinterpreted that way.

The real Leigh said:

Absolutely true.

Two blocks that are absolutely clinically scientifically clean will not wring.

The common solution to that problem is to rub one face on a finger. It picks up enough skin oil to do the job.

- Leigh

Click to expand...

I've never had trouble just breathing on one block or the other, though my practice is to rub the block over the clean inside skin of my wrist. ;-)

Like you said, We don't really know what the film is made of, though we can try to describe the mechanism of it's effect. Have you ever tried to dislodge that last bit of dust from a "Scientifically clean" surface?* Don't underestimate the powers of molecular attraction!

* Yes, I have, Cleaning prior to vacuum coating to a 20/10 or better Scratch/dig spec can drive one to distraction!

Other than putting 40 blocks in a stack I wonder how many here would know the difference of this film.
Where exactly do people here use a stack where the gauge in use can R&R well inside the variation.
It seems kind of pointless.
Bob

Hi Bob,

The whole point is that by including one measured film thickness in the certified length of the block, you can stack as many as you wish.

That will not introduce any error in the sum of the individual lengths.

The other options, i.e. including zero or two film thicknesses for each individual block, both require additional calculations for the stack.

- Leigh

CalG said:

Like you said, We don't really know what the film is made of,

Click to expand...

If that is actually true, i.e. not to be found after a thorough search of the scientific literature of the past three decades, it only means no one has applied modern surface analysis techniques to the problem. Auger spectroscopy. X-ray Photoelectron Spectroscopy (XPS), Raman, etc. could determine the composition of the film and the nature of the bonding to the surface. If it already hasn't been done.