Measuring customer parts on a CMM - How many decimals to report to the customer?

Eredhel

Quality Manager
#11
Like Roxanne I'm not intimately familiar with 17025. But I don't believe your CMM is a calibration standard, you even mention that you use an NIST traceable standard for your CMM.

Are you trying to use your CMM as an NIST traceable calibration device as well as an inspection tool? I might also be misunderstanding what your goal is.
 
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Ninja

Looking for Reality
Staff member
Super Moderator
#12
The customer parts in this case, are glass measuring scales, for which they would like calibration data of specific line to line distances.
I think your use of this word is causing the confused responses...data is data...

Being that it seems like there are two languages being spoken here...please allow me to ask this:

"What, specifically, is the customer paying you to do?"

If it is to measure the distance between lines on a piece of glass...your 17025 has no part of the conversation and has confused the issue.
You are doing toll measurement work...period.
If it is instead to issue a calibration certificate...that's another story.
 

greif

Involved In Discussions
#13
Yes the customer wants a calibration certificate and yes he wants lines measured on a piece of glass.
I seem to recall some confusion between inspection, calibration, and verification by different groups and the US and Europe; maybe there is some of that going on here.

Calibration of an item does not need to be directly to a "standard" (ultimately the only standards are SI unit items), almost all calibrations are done by a chain of traceability. Even the fancy machine NIST used to measure my master scale, was checked against other scales and end standards.

I brought up 17025 because there are specific reporting requirements required by it, and the customer wants a 17025 accredited calibration certificate (in the future for us, not there yet).

But back to my original question, which is more basic metrology and trying to do things in an industry accepted way:
If we measure the part 3 times and get; 50.000, 50.000, 50.002mm, is it ok to report 50.0007mm (along with the associated uncertainty)?
 

Eredhel

Quality Manager
#14
Keep in mind some standards specifically require traceability to NIST. And I know of one standard that gets even more specific and says that you cannot use a "moving" device as a standard. This is one of the reasons for asking these kinds of questions.

Edit: An example of calibration against standards that gets more specific, "Verification against identified acceptance criteria is performed on nonadjustable equipment."
 
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Eredhel

Quality Manager
#15
I should mention that "nonadjustable equipment" requirement isn't even for a calibration house, it's a QMS requirement for manufacturing of components and assemblies.

Edit: I forgot to mention your original question you put back out there. Another tricky thing here is that technically there is no rounding allowed to be done with decimals. But I didn't want to mention that until we knew more about what you were really trying to do.
 
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greif

Involved In Discussions
#16
I don't follow; how would you measure a glass line scale (not a short one, say 100mm long) on a non-moving device?
I do like the idea of the part remaining stationary (it does on my CMM, the x and y move on air bearings while the part sits on the granite). But still has moving parts.
 

greif

Involved In Discussions
#18
Sooooo..... a non-adjustable scale is used to calibrate my CMM, then the CMM is used to measure the customers glass scale. No problem, right?
 

Jim Wynne

Staff member
Admin
#19
Customer does not state tolerance, only wants measurement reported.
Here is what I've been able to deduce from the information provided so far:

  • If there is no tolerance, it means that for practical purposes the lines can be anywhere, and the customer wants the location of them (relative to what, I don't know) measured. This is not calibration.
  • You wrote, "Calibration does not require adjustment, so calling it calibration seems proper." You are correct that "calibration" doesn't imply that adjustment is necessary. It does, however, require comparison to a standard. Your CMM/microscope is not a standard in this sense, thus you are doing simple measurement, not calibration.
  • Eredhel wrote, " An example of calibration against standards that gets more specific, "Verification against identified acceptance criteria is performed on nonadjustable equipment." I don't know the source of the quote, but it's wrong. All calibration is verification, but not all verification is calibration. Again, calibration is comparison to a standard, period.
  • You wrote, "
  • ...when I sent my standard scale to NIST, they did what I am doing for my customer..." No. They compared your scale to a standard, and presumably a tolerance was involved, or will be involved in the use of your scale. Not calibration
Again, based on the information available here, you are not doing calibration.
 

Eredhel

Quality Manager
#20
Here is what I've been able to deduce from the information provided so far:

  • If there is no tolerance, it means that for practical purposes the lines can be anywhere, and the customer wants the location of them (relative to what, I don't know) measured. This is not calibration.
  • You wrote, "Calibration does not require adjustment, so calling it calibration seems proper." You are correct that "calibration" doesn't imply that adjustment is necessary. It does, however, require comparison to a standard. Your CMM/microscope is not a standard in this sense, thus you are doing simple measurement, not calibration.
  • Eredhel wrote, " An example of calibration against standards that gets more specific, "Verification against identified acceptance criteria is performed on nonadjustable equipment." I don't know the source of the quote, but it's wrong. All calibration is verification, but not all verification is calibration. Again, calibration is comparison to a standard, period.
  • You wrote, "
  • ...when I sent my standard scale to NIST, they did what I am doing for my customer..." No. They compared your scale to a standard, and presumably a tolerance was involved, or will be involved in the use of your scale. Not calibration
Again, based on the information available here, you are not doing calibration.
It's a quote from the API Q1 standard. And it is specific to their requirements for what kinds of standards are allowed to be used to calibrate/verify measuring equipment. It's accurate, and quoted verbatim. I used it as one example of an outlier, not that all QMS standards are like that.
 
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