Hello,

I have been working in ISO for only about 2 years now and I need a little help. This is really kind of simple but I want to make sure I do it right. Here's the situation. We have been ISO certified for about 4 years. We have always done our calibation out of house and I would like to bring it in house.
This may be very difficult in some factories but in we only calibrate tape measures and rulers.

Now can we just use say a 5 foot hard metal ruler and get that calibrated out of house and traceible to NIST and then calibrate the tape measures off of that ruler????

That was my thought but I don't know anyone who does it so I really don't know if it is legal through ISO.

Please help me with this.

Thanks Carol

Hello.
We bought a calibrated steel rule which was already certificated. It was designated "Master" and is not used for day to day measuring. All other tapes and rules are checked using this one and a "calibrated" sticker attached. We also have an inventory of calibrated tapes. Our procedure states that calibration check will be carried out on receipt of new tapes. Thereafter, metal tapes should not need rechecked if they are kept in reasonable working conditions as they will not shrink or expand. It is encumbent on the equipment holder to ensure that it has a calibration sticker, it is not damaged and the scales are readable before use. This check is signed for on our batch paperwork. No complaints from auditors so far.
Regards :)

Interms of the TAR (Test Accuracy Ratio), yes the metal ruler is more accurate.....

But the first question is, why calibrate a ruler or measuring tape?

I don't know!!!!! When I started doing ISO for the company they were already calibrating tape measure and rulers so I just figured that it had to be done. I always thought it was strange but never questioned it. I guess I just assumed that they had to be because they have been doing it for so long.

Do they have to be?????
What will they auditor say if they are not???

The calibration method sounds fine, I've been doing something similar for nearly 10 years and its been OK for two versions of ISO 9001, QS9000 and ISO/TS 16949. As for do you need to
calibrate, ask this question, do you make product-quality decisions based on what the gauge/instrument is saying? If your
answer is Yes, then you need to know the status of the gauge/instrument you are using, so get calibrating.

10 years with tape measures and they must be calibrated if used for accepting product. The clip on the end becomes loose from letting them snap back in place.

My personal opinion.....nothing more.....calibrating tape measures and most rulers is a silly waste of money.....BUT

Some of the high end metal ones could reasonably be expected to be cal'd, but realize that even they are unreliable below 1/32 inch.....measuring tapes are unreliable below 1/16 inch.....that is, they may indicate some value, but how believeable that value is.....

In reality, if you need a tight measurement, you will use something else to measure if at all possible.

Sometimes, the length dictates use of a rule or tape, and then you are stuck.....unless you expand the tolerance to 1/4 inch or better.....then the rule or tape is adequate.

Just my opinion.

Hershal

Oh, one other point.....if the cal of the rule and tape will happen regardless.....don't forget to have the accredited calibration including measurement uncertainty, so when a measurment is performed with the rule or tape, you know that the true value is x +/- MU.....and the MU of the actual reading will be larger than the MU coming from the cal lab.

For example, a cal lab might report its MU as 0.1 inch, but the user would actually have a MU likely around 0.25 inch, so the measurement performed with the tape would be x (value) +/- 0.25 inch over some length (say, 18 inches).....and a different MU value beyond that length.

So unless the tolerance is wide, or length requirements leave almost no other choice, I would say not to cal therule or tape.

Just my opinion.

Hershal

My personal opinion.....nothing more.....calibrating tape measures and most rulers is a silly waste of money.....BUT

Some of the high end metal ones could reasonably be expected to be cal'd, but realize that even they are unreliable below 1/32 inch.....measuring tapes are unreliable below 1/16 inch.....that is, they may indicate some value, but how believeable that value is.....

In reality, if you need a tight measurement, you will use something else to measure if at all possible.

Sometimes, the length dictates use of a rule or tape, and then you are stuck.....unless you expand the tolerance to 1/4 inch or better.....then the rule or tape is adequate.

Just my opinion.

Hershal

I agree with Hershal! That having been said I do recall going through similar calibrations when performing wire harness work on the Abrahms tanks for General Dynamics! We used procedures just like the ones posted here already. It was a Mil-I environment and I could never talk them out of it. Some of the wire harnesses were 40 to 50 feet long and most were built on a certified wire board. Didn't matter to the GD auditors;i.e. calibrate the tape !!!
:whip:

Hello Carol:

When you say you have been working in ISO for 2 years, what do you mean by "ISO?" ISO 9001:2000? ISO 17025:1999? ISO/TS 16949:2002?

If you mean ISO 9001:2000, you might want to think about your use of the term "calibration." You may really be verifying your measuring equipment as required by 7.6 Control of monitoring and measuring equipment. The connotation with the use of the term "calibration" is peculiar in relationship to tape measures. But if you think of it as verifying your measuring equipment, the intent of the requirement may make more sense.

Regards, Dirk

...calibrating tape measures and most rulers is a silly waste of money...In reality, if you need a tight measurement, you will use something else to measure if at all possible.
My opinion as well - many have read my rants on the subject in other threads. In our shop they are used for 1) measuring overall dimensions of the parts so we can order wood crates for shipping and 2) the saw operation. Both have unilateral tolerance (minus nothing, + something). The tolerance for the boxes is wide open, it just has to be a little bigger than the part in every direction. The saw has -0/+1/8" - but if he goes over - so what - the lathe is the next operation and is responsible for finished part oal. The saw guy might catch some **** from the lathe operator if it is way to long, but nothing is getting scrapped.

There is no way - IN OUR SHOP - that I would spend any time or money verifying/reverifying (you cannot calibrate tape measures or steel rules - once they are etched or printed, that's how they are forever) or purchasing an expensive "certified" tape measure or scale. Besides - as db pointed out in another thread not too long ago - the retracting mechanism tends to be the most common demise of tape measures - we are constantly replacing them.

Tape measure follow up - These are used on cables ranging from 6' to 120' with tolerences of +/- 1/2". That is why they are used. Gage R&R's have also been performed. Yes the results were not good, but our customers realize we are not making parts for the space shuttle so the are fine with us using them. Remember to keep it simple!

You guys are very helpful and I appreciate all your advise. Let me explain our company a little to help you understand our process.

We run a fiberglass plant in Michigan. We are ISO 9001:2000 (sorry for not clearifying earlier). We built about 500 different fiberglass parts for several different companies. Tape measures are used for things like placement of wood in the bulk of the glass. Example: Place wood 2" from front edge and 4" from left side. They are also used for grinding the holes in the fiberglass. The wood location does not have to be precise but the location of holes does.
So yes the tape measures do affect the part so they must be calibrated.

I just wanted to make sure that I could calibrate against a certified metal rule.

Thanks to all

Hello Cari:

If you don't spend any time or money verifying tape measures, how do you know you have to replace them?

Also, when you get a new tape measure, how do you know that the length it describes (inch, foot, meter, etc.) is really an inch, foot, meter, etc.? What tolerances are you allowed? How do you know you are within that tolerance?

Thank you, Dirk

Pressed for time just now....will elaborate on the tapes later.....just a quick point......a tape that goes 120' can be cal'd with a five foot rule.....but the MU will be terrible.....

Hershal

OK, I have more time now......

A five foot ruler, into a maximum 120' is 24 times.

Yes, the firve foot ruel can cal the 120' tape.....BUT.....the MU (hence, the actual measurement) will likely be bad.....

Using resolution error of the tape and rule, alingment error because the tape or rule must be scooted.....parallax error, temperature coefficienct of expansion, the tip wobbling by about 0.25 inch......and 10-20 readings all varying by as much as 0.25 inch.......

I did a rough calc and came up with between 1-1.25 inch MU as cal'd.....NOT AS USED.........

Meaning the actual reading (with 95% certainty) is 120' plus/minue 1.25 inch, as cal'd.......

As used can expand to as much as 1.5 inch, so the true measurement, if you are 95% certain, may be as much as 120' plus/minus 1.5 inch.....

A solid study will adjust the MU up or down......

That is a good reason not to cal tapes.

Hershal

Hello Cari:

If you don't spend any time or money verifying tape measures, how do you know you have to replace them?

Also, when you get a new tape measure, how do you know that the length it describes (inch, foot, meter, etc.) is really an inch, foot, meter, etc.? What tolerances are you allowed? How do you know you are within that tolerance?

Thank you, Dirk
Hi Dirk

The guy who uses it says "Cari, I need a new tape measure please. This one is broken."

I explained the use and tolerance in my previous post. I probably could have been clearer in that our saw operation is cutting bar stock. The length for the saw op is the part oal +1/8". His tolerance is +1/8"/-0. So if our part oal is 12", the router tells the saw operator to cut it 12-1/8" +.125/-0. The lathe operation needs a little extra stock so they can square up and face off to the final part oal.

No way is it necessary to spend time or money on this here. Tape measures and scales are not precision instruments. If I was at all concerned, I would choose something other than a tape measure to use for that measurement.