Exempt from Calibrating our Tape Measures and Micrometers

[Jen Kirley]

Next question... Where is a good place to purchase a nice NIST gage block set?

Now there's an open-ended question! I did a Google search using key words "gage block set' and came up with over 7 million "hits."

So I am going to start you off with The Gage Block Handbook.

The handbook is over 100 pages for good reason. There are many kinds of gage blocks. "Which is right for me?" is the question I can't answer for you. Page 8 shows the tolerance sensitivity for various grades. The tighter the tolerance level, the more expensive the gage block.

There are also different materials. Ceramic gage blocks cost less than the steel ones as I recall, but they also wear faster so consider that when deciding what to buy.

Once you determine what type to buy, who to buy from is the easy decision. You can buy direct from the makers: Mitutoyo, Fowler, Starrett, etc, or through Grainger, a different supplier, Amazon.com etc. You can compare at Nextag. Just make sure you get certificates of calibration with them.

There's a thread titled Calibrating or Verifying Metal or Steel Tape Measures that pretty extensively discusses the subject of steel rules and tape measures.

I hope this helps!

 

[Jim Wynne]

I agree with Brad and Ron.

I cannot see how the example you give provides exemption.

You will have to calibrate.

It's usually a good idea to avoid imperative declarations unless you're sure about the particular situation at hand, and I wish people would refrain from knee-jerking when it comes to when calibration is required. ISO 9001:2008, 7.6 says that calibration (among other things) is required where necessary to ensure valid results. If it can be demonstrated that valid results may be consistently assured without calibration, calibration isn't required.

 

[The Specialist]

Can I get away with saying we are exempt from calibrating our tape measures and micrometers due to the fact that we have a variance in our product from our supplier. a lil background. we use micrometers to check our thickness on our metal which will vary depending who we received it from, and as long as it is within a +- say 1/8 inch then its is ok. same thing goes for our cuts which we use our tape measures for as long as we cut to an 1/8 of an inch can we get away with saying we do not need to use a metal rule or gage to check our tape measures for accuracy.

Jim Wynne said:
"It's usually a good idea to avoid imperative declarations unless you're sure about the particular situation at hand, and I wish people would refrain from knee-jerking when it comes to when calibration is required. ISO 9001:2008, 7.6 says that calibration (among other things) is required where necessary to ensure valid results. If it can be demonstrated that valid results may be consistently assured without calibration, calibration isn't required."

My interpretation of the OP is that it IS a requirement for measurement acuracy to be within a pre-determined tolerance, as there is a tollerance applied to the OP's process (QC testing of incomming material) (if a large one)

How is it possible to determine that the 'measured object' (Supplier's process output, in this case) is suitable, to within defined tolerances, if the accuracy of the measuring device is unknown?

 

[Jim Wynne]

Jim Wynne said:
"It's usually a good idea to avoid imperative declarations unless you're sure about the particular situation at hand, and I wish people would refrain from knee-jerking when it comes to when calibration is required. ISO 9001:2008, 7.6 says that calibration (among other things) is required where necessary to ensure valid results. If it can be demonstrated that valid results may be consistently assured without calibration, calibration isn't required."

My interpretation of the OP is that it IS a requirement for measurement acuracy to be within a pre-determined tolerance, as there is a tollerance applied to the OP's process (if a large one)

How is it possible to determine that the 'measured object' (process output, in this case) is suitable, to within defined tolerances, if the accuracy of the measuring device is unknown?

"Pre-determined tolerance" is not necessarily relevant. What is relevant in all cases is whether or not calibration is needed to ensure valid results. As I suggested earlier, if it can be demonstrated that valid results are consistently achieved without calibration, what value is there in calibration, and how can you say, in imperative fashion, "You will have to calibrate"?

If I have documentary evidence that my measurements achieve valid results--there are no (or reasonably few) nonconformities traceable to inaccurate measurement devices--calibration not only isn't required, it's wasteful.

Can you demonstrate, unequivocally, in the OP's situation that calibration is necessary to ensure valid results? If not, then the only sensible answer to the OP's question is reference to the standard, and "It depends..."

 

[The Specialist]

Technically though Jim, I should have asked:

Is the thickness of the metal sheet supplied ‘critical’ to your process? i.e. will the thickness of the material impact on the quality of your final product? Is the thickness of the material, to within pre-determined tolerance, declared as part of your product design and design history file?
Will the inaccuracy of the thickness of the material compromise your QC or quality management system by way of its non-conformance with specification?

If any of the above are true, you need to apply (if you haven’t already) a specification for the allowable inaccuracy of thickness.
You will need to make sure that your measurement device/instrument is calibrated.
You will need to factor in the inaccuracy of your measurement device in any measurements taken (+/-) when QC passing the incoming material.

 

[The Specialist]

"Pre-determined tolerance" is not necessarily relevant. What is relevant in all cases is whether or not calibration is needed to ensure valid results. As I suggested earlier, if it can be demonstrated that valid results are consistently achieved without calibration, what value is there in calibration, and how can you say, in imperative fashion, "You will have to calibrate"?

If I have documentary evidence that my measurements achieve valid results--there are no (or reasonably few) nonconformities traceable to inaccurate measurement devices--calibration not only isn't required, it's wasteful.

Can you demonstrate, unequivocally, in the OP's situation that calibration is necessary to ensure valid results? If not, then the only sensible answer to the OP's question is reference to the standard, and "It depends..."

How do you suggest that you determine the accuracy of a measurement taken from a measurement device that has not been calibrated and the accuracy of the device is unknown?

 

[BradM]

My interpretation of the OP is that it IS a requirement for measurement acuracy to be within a pre-determined tolerance, as there is a tolerance applied to the OP's process (QC testing of incomming material) (if a large one)

How is it possible to determine that the 'measured object' (Supplier's process output, in this case) is suitable, to within defined tolerances, if the accuracy of the measuring device is unknown?

I certainly am not trying to speak for anyone here, but to me, the key word is "management".

Section 7.6 requires management. It requires observing the program, the intended results, the requirements, etc. and make a determination. To the point, I think having to verify a tape measure periodically is fairly pointless (my opinion). I can demonstrate that a tape measure pretty much does not change from month to month. However, a micrometer due to wear, warp, mechanical adjustment, etc., can change, thus changing the results. Thus, calibration may be in order.

It's making calibration decisions based on the risk, need, and use, and much less about procedural requirements.

 

[The Specialist]

I certainly am not trying to speak for anyone here, but to me, the key word is "management".

Section 7.6 requires management. It requires observing the program, the intended results, the requirements, etc. and make a determination. To the point, I think having to verify a tape measure periodically is fairly pointless (my opinion). I can demonstrate that a tape measure pretty much does not change from month to month. However, a micrometer due to wear, warp, mechanical adjustment, etc., can change, thus changing the results. Thus, calibration may be in order.

It's making calibration decisions based on the risk, need, and use, and much less about procedural requirements.

I agree that you will not routinely ‘calibrate’ a steel rule. However, you will need to purchase one that has been tested against a reference standard and can be determined to be ‘accurate' from purchase.

The term ‘calibrated’ is a bit loose in this instance.

 

[BradM]

How do you suggest that you determine the accuracy of a measurement taken from a measurement device that has not been calibrated and the accuracy of the device is unknown?

This is a very valid point. However, this is step 2.

Step 1 is determining if you even care if the instrument is accurate or not.

Again, reasonable minds can differ on these issues. I take the more extreme approach. Too much money is wasted on equipment many times. If you don't need it and it doesn't matter, get rid of it. What's left matters, and should have some verification made in it.

 

[Jen Kirley]

Technically though Jim, I should have asked:

Is the thickness of the metal sheet supplied ‘critical’ to your process? i.e. will the thickness of the material impact on the quality of your final product? Is the thickness of the material, to within pre-determined tolerance, declared as part of your product design and design history file?
Will the inaccuracy of the thickness of the material compromise your QC or quality management system by way of its non-conformance with specification?

If any of the above are true, you need to apply (if you haven’t already) a specification for the allowable inaccuracy of thickness.
You will need to make sure that your measurement device/instrument is calibrated.
You will need to factor in the inaccuracy of your measurement device in any measurements taken (+/-) when QC passing the incoming material.

Such demonstrates how tricky it can be to give good advice here. Notice how I went along, tippy tappy happy, and offered advice on gage blocks without knowing for sure that poprock7 needs them. I still don't know if they are needed. Did I mislead the OP? I don't know. I hope not.

To all:

And so it goes: in a place like this, advice is offered without specifc guarantee as to its accuracy. Our diversity is our strength, but that sometimes sends mixed signals. We can add, subtract and divide; we can correct ourselves and each other as a group, and we should. But let us do so gently please.