Must a vernier caliper and a rule be calibrated according to ISO 9001?

somashekar

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#21
Re: Must a vernier caliper and a rule be calibrated?

Taking a look at the attachment, its a metal measuring tape which is said, which has a small L bend at user end. Typically this L bend is 1 mm thick and is hooked to have a play of 1 mm. Depending on the type of measurement (butt in or butt out) you still get the desired reading at the place where you intend to take the measurement.
I have used one such for a critical length measurement of a vacuum formed ABS bed, and in this case as the L bend comes to use regularly, we have got the tape calibrated from source ( to our desired measure) and have discarded the tape after three months of use. No recalibration what so ever as its better and cost effective to get a new tape with calibration from source.
Hope this gives you a lead
 
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bobdoering

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#22
Re: Must a vernier caliper and a rule be calibrated?

...we have got the tape calibrated from source ( to our desired measure) and have discarded the tape after three months of use. No recalibration what so ever as its better and cost effective to get a new tape with calibration from source.
This is one approach to handling the calibration issue. Although, a more comprehensive approach would be to take a gage block to the hook before disposing to ensure that the most recent measurements were indeed acceptable. It would be the most likely source of error, if any.
 

Jim Wynne

Staff member
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#23
Re: Must a vernier caliper and a rule be calibrated?

Was the meter rule calibrated from the factory? Do you expect it to work forever with no wear where it is at? Then essentially you are saying that the gage is calibrated and you have a 99 year calibration period - and that particular auditor essentially agreed with it.
A lot (probably most) of the angst and confusion over calibration of tape measures, etc. is due to sloppy engineering specifications. There are too many situations where a tolerance of plus or minus half an inch would do just fine, but the block tolerance says the spread is .020", and off we go. In general, we should be able to assume that if a thing is measured with a ruler or tape measure, it's not critical and be done with it. Furthermore, auditors should be able to recognize those situations and move on to something meaningful.

I might have told this story here before, but I once assumed the position of quality manager for an OEM (not automotive) that dealt quite a bit with sheet metal. One of the first things I noticed in the incoming inspection area was an 80" vernier caliper, and naturally I was interested in knowing what it was used for. Long story short, it turned out that it was used for measuring sheet metal panels that were ~ 5' long and the drawing tolerance (the block tolerance, of course) was +/- .010" on the OAL. A few minutes of investigation revealed that there was at least 3/8 of an inch of "slop" in the assembly, and a tape measure would have been just fine. I took it up with the design engineer, and he changed the tolerance, and for all I know the 80" caliper is very dusty by now.
 
S

Sorin

#24
Re: Must a vernier caliper and a rule be calibrated?

Likewise..., we have demonstrated that such meter rule is used at inwards goods inspection of the cable as well as in the process and final inspection, and we have a dimension of xx (+/- 3mm) to meet. The meter rule is fixed at the workbench, and is not subjected to any handling or wear when in use. The persons are trained to read the measurement. Enquires on internal complaints and customer complaints about cable length was audited and found none existed. Registrar's accepted our approach....
That auditor (from the client) was out of his mind....
 

bobdoering

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#25
Re: Must a vernier caliper and a rule be calibrated?

A lot (probably most) of the angst and confusion over calibration of tape measures, etc. is due to sloppy engineering specifications. There are too many situations where a tolerance of plus or minus half an inch would do just fine, but the block tolerance says the spread is .020", and off we go. In general, we should be able to assume that if a thing is measured with a ruler or tape measure, it's not critical and be done with it. Furthermore, auditors should be able to recognize those situations and move on to something meaningful.
This is true. And, what they can draw is not what it looks like in real life, too. We used tape measures all of the time for cutting foam. The good news? No gage pressure. But, they were still calibrated. Again, calibration for a tape measure is not the same as a micrometer - for a reason. Nobody is asking anyone to look at the tape end with optical flats for wear. But, people perceive that the big "CALIBRATION" word means the same diligence for every type of gage. That is just abject lack of comprehension. It is understandable, as the perception of calibration is more urban legend than fact for many people. That creates the angst.
 
J

JaneB

#26
Re: Must a vernier caliper and a rule be calibrated?

A lot (probably most) of the angst and confusion over calibration of tape measures, etc. is due to sloppy engineering specifications. There are too many situations where a tolerance of plus or minus half an inch would do just fine, but the block tolerance says the spread is .020", and off we go. In general, we should be able to assume that if a thing is measured with a ruler or tape measure, it's not critical and be done with it. Furthermore, auditors should be able to recognize those situations and move on to something meaningful.
Yes, exactly.

The Standard does not simply say 'Calibration shall be performed on all measuring equipment'.

It precedes, and thus qualifies (ie, limits its meaning), the requirement with 'where necessary to establish valid results'.

Jim's quite right - often the set specifications are sloppy. I've even seen specifications demanding such a fine tolerance that not only wasn't it required, it couldn't actually be achieved with the tools the machine shop was using. Silly. Change the specs to something realistic and achievable, and then no problem.
 

bobdoering

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#27
Re: Must a vernier caliper and a rule be calibrated?

The Standard does not simply say 'Calibration shall be performed on all measuring equipment'.

It precedes, and thus qualifies (ie, limits its meaning), the requirement with 'where necessary to establish valid results'.
True. I agree that is what the standard says. It also does not preclude the use of plastic calipers and key chain tape measures.

My point was that in spite of what the standard says, if you are going to bother to measure something, you ought to be certain the device is measuring correctly. That is the point of calibration. There is just an undue fear of the concept - probably from basic ignorance of its true meaning and the problem of other standards that have muddied the problem by overspecifying the calibration process requirements. That fear causes people to spend more effort figuring out how to con their way out of calibrating, rather than simply doing what is necessary. It is not an uncommon reaction.

If you are not concerned that the gage is measuring correctly, then the logic would support no need to measure at all. It doesn't matter. Do a visual for that matter.


I've even seen specifications demanding such a fine tolerance that not only wasn't it required, it couldn't actually be achieved with the tools the machine shop was using. Silly. Change the specs to something realistic and achievable, and then no problem.
Generally overspecifying should have a more significant impact on gage R&R (used to choose the correct gage) than calibration (verifying the correct gage still reads correctly).
 

Jim Wynne

Staff member
Admin
#28
Re: Must a vernier caliper and a rule be calibrated?

If you are not concerned that the gage is measuring correctly, then the logic would support no need to measure at all. It doesn't matter. Do a visual for that matter.
It's a question about whether it's worthwhile to worry about whether a device is measuring "correctly." If you know that your device is adequate to the task (which is often the case with tape measures) you shouldn't have to be concerned about calibration, even in the broadest sense of the term.

Generally overspecifying should have a more significant impact on gage R&R (used to choose the correct gage) than calibration (verifying the correct gage still reads correctly).
For the types of tasks I'm referring to, R&R shouldn't be necessary either. We should make sure that operators know how to read a tape measure and then let them do it.
 

bobdoering

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#29
Re: Must a vernier caliper and a rule be calibrated?

For the types of tasks I'm referring to...
Yes, I suppose that is adequate for Quality Level TCE. For that, there is never any fear of mis-measurement. They really should make that a part of the standard. There would be unbridled supplier support.
 
Last edited:
J

John Nabors - 2009

#30
My typically uninformed :2cents: on the OP's original question:

The diameter of the eyelets that compensate for the thickness of the tang on a tape rule are subject to wear (what we rednecks here in the southern US call 'gittin' wallered out'). If the tape rule is used to verify conformance of the product it measures to customer requirements, yup, you need to calibrate it.

Vernier calipers, like all calipers, are subject to wear on both the inside and outside measuring faces (not to mention dents and dings). With verniers, you don't have quite the same danger (as with dial and digital) of zeroing on the blades for outside measurement resulting in double error on the blades for inside measurement, but they still wear. Once again, if it is used to verify conformance to customer specs, calibrate that puppy. My preferred, completely arbitrary calibration intervals for such tools has been 6 months unless the calibration history of the gage indicates a tighter or more relaxed interval.

Even if a gage has no moving parts whatsoever (such as a 6"/15cm steel rule), usage results in some wear, possibly infinitetesimal, but wear nonetheless. My feeling is that you owe it to your customers to know with certainty that the tools you use to verify conformance to their requirements are capable of doing so.

Once again, just my :2cents:

Kind Regards -John
 
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