Tape Measure Calibration - I asked if I had to do nominals, was told no!

L

louie

#1
Recently had pre-assessment audit and auditor says we must calibrate our tape measures as they are used as an in process inspection tool to measure length of material. The measurements we take are not critical measurements. If a piece is to be 6 " long, we have no tolerance to check to....

BUT the person 'calibrating' the tape measures does not need any formal training... just check the tape measure for deterioration and measure a calibrated block to see if it measures the same. When asked if I had to do nominals, was told no, just pick a length and check that. no difference on length to check no matter what the length of the tape measure?

Any one else have history with tape measure calibration?

Thanks
 
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P

pdboilermaker

#2
We use hard 160mm scales to measure stitch length. These were "calibrated". Our instructions are written somewhat like this.
1. Get in new scale
2. Measure gauge blocks to confirm accuracy
3. Put on calibration sticker
4. Check scale visually every 90 days for things like bent, broken, numbers worn off.
5. New calibration sticker

I know, I know lame as can be but it works when you come across an anal non pragmatic auditor.
 

Jerry Eldred

Forum Moderator
Super Moderator
#3
I am probably somewhere halfway between being a non-pragmatic auditor, and a practical type, as I have many years in calibration/metrology, and also some background in QS9000/ISO9000 and other quality systems auditing. So take my answer from that context.

From a quality systems perspective, it sounds like you have an ambiuguous requirement in your quality system.

You require the lengths of material to be checked (implying that you do care about length), and yet there is not an allowable pass fail criteria. It seems there needs to be a management decision as to whether they want to apply some pass/fail criteria (i.e.: if you measure what is supposed to be six inches, how much deviation is allowable?)

I am not in your process, so I don't understand what the spec truly ought to be. But in my humble opinion, I would suggest that you set some pass/fail limits on your measurements, make that your tolerance. If you already have gauge blocks, no further investment needed. But another method, depending on what tolerance you decide to certify your tape measure to (I recommend about ten times tighter than whatever spec you assign to your pass/fail criteria for the process measurement), would be to get about a 36 inch straightedge ruler (metrology grade) from one of the good dimensional instrument manufacturers. Use that as your standard. The manhours to check a tape measure would be less.

The other question that comes to mind is... is the measurement you make a deliverable? That is, do you measure to be sure a correct amount of material or whatever is supplied to the customer that you agreed to provide, based on that measurement? If that is the case, then you most definitely need to calibrate. But if, on the other hand, that measurement is only a 'convenience' measurement that does not have any impact on product quality in any way (including providing a dimension agreed to provide to the customer), then I would recommend not calibrating. But by al means, document those details, and place a NO CALIBRATION REQUIRED label on each and every tape measure. You can buy those labels quite cheaply from companies such as Brady labels.

It does come back to that age old question as to whether or not to calibrate. Calibrate if the measured parameter assures you provide something quantitative to your customer, or if there is safety or reliability or quality of the product based on that cal. Don't cal if none of the above are impacted by the measurement.

Hope I have been of help.

------------------
 
#4
Our primary measuring device in use on the floor is the 16' tape measure. We were also requested to present evidence of calibration based on results of our pre-assessment audit. I purchased a "starrett" 16' tape with a long form cert., I then compare the two and record the results. Our tolerance is 1/8".
I was also asked for a MSA on the tapes. That too was enlightning; No two people could come up with a reading close enough to record. After lessons in the proper use of the tape I was able to put together a presentable MSA.
Lesson Learned; Make every attempt to comply with the requirement, it may be beneficial.
 
M

MarilynJ6354

#6
Tape Measures

We use tape measures more than anything else so they are calibrated monthly against a calibrated 36" steel rule. We take three measurements: 6", 12" and 24" but locations that sell larger items use different measurements when calibrating.
 
A

Al Dyer

#7
Can a tape measure be calibrated or is it "verified" to a traceable standard?

I guess it comes down to the discrimination required for the measurement taken. Nobody would use a tape measure to discriminate a thousanths?????

Al...
 

Hershal

Metrologist-Auditor
Staff member
Super Moderator
#8
A number of our accredited test labs and inspection agencies use tape measures (such as the ones they buy from Home Depot or Lowes) for various measurements. Al, yes, a tape measure can in fact be calibrated. However, I think it is silly and a pointless waste of money.

I tell our accredited inspection agencies that I certainly agree with having an accredited calibration lab check the tape ONCE when it is new....but if it is not damaged, then it is unlikely to change. The exception is the tab on the end which will start to slide around and throw you off by as much as 1/4 inch.

Remember, a tape measure is pretty much useless below 1/8 inch resolution anyway. It is useful for longer lengths, but not for small resolution. Also, thermal expansion will throw you off. Put another way, if you are in MN or in AZ....the thermal effects, plus the resolution and parallax issues will give you a large uncertainty value, especially if you are trying to read under 1/8 inch at almost any length.

It is obvious to me that the auditor in this case has no Metrology training or experience.....I would complain to the AB, and ask why the auditor was auditing something where the auditor is apparently not competent (AB term for proficient).

Just my thoughts.....

Hershal
 
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