We recently received a minor nonconformance during a surveillance audit. The finding concerned the calibration (or lack thereof) of tape measures used on our production floor. These tapes are used to confirm lengths after a cutting operation. I am looking for a logical, simple method for calibrating tape measures. Does anyone have any "best practices" to share? I appreciate the assistance.

Dom-

I think that you may need to provide more information on the subject.

Are the tapes used to "determine acceptance of the product" for movement to the next function area or for shipment?

If not, label them as "reference tools" (assuming that you have some other method of measuring/testing the product for conformance to specification.

If they are, I believe that you may be in a pinch. Tape measures are subject to so much regular abuse, malformation, and other circumstances that would impact their accuracy (to some tolerances) --> you might find yourself hard pressed to keep them calibrated (or spend a ton of time rechecking them).

Apologies for only being semi-helpful. Throw some more details out there so that those more knowledgeable than I on the subject can give you some better advice.

ALM

dscumaci: I must agree with ALM, more info is needed to give a helpful reply.
What type of verification is used at your facility to determine calibration of tape measures as specified under your calibration procedures?

------------------
GSH
Quality Mgr.
QS9000 Coordinator

Gentlemen,
Thank you for your response and I apologize for the vagueness of the question. To clarify the matter, the tape measures are used to make accept/reject decision after steel bar has been cut. Tolerances for length of bar and plate range from 1/4" and 1/16". However, my question is what my be a logical means of calibrating the tape measures? Does anyone have experience implementing a process for calibrating tape measures? What are some options we may have?

Thank you for your help;

Dom

You can't calibrate a tape measure (because you can't adjust it to bring it back into conformance), but you can verify aspects of it. You can verify that it is still readable and you can compare it to a standard (if you suspect warpage, for instance). One option is to verify it at incoming inspection and then establish reasonable intervals for verification. Also, come up with rules of action, such as what to do if the tape measure has been dropped or been exposed to unusual wear conditions.

Remember to keep in mind that you are required to calibrate equipment through their usable range. Purchase the right Tape measure for the job. To add to Roger's post, consider the things that break or become loose (i.e. the end-hook on the tape measure). Is there any play?

Do you need to consider the "readibility" factor, where the measurement device must read one more decimal than the stated tolerance? 1/16 is .0625. Your device should be readible to .006? (1/125?) This may be splitting hairs, but could this be an audit target, and more importantly an issuue for you? I guess it depends upon the criticality of the measurement.

keep a steel rule for verification when tape gets worn/abused ...discard (or tag) and replace with a new one when wear reaches an unacceptable level...the steel rule comes in calibrated/verified or what ever........and if not heavily used has an infinitye cal cycle....or tap on one of 15 years.....You set the rules, what makes sence for you

I agree with Barb's recommendation. Currently, our program to calibrate a tape measure includes verification that the end-hook does not have too much play (dependent on the nature of the tolerance and item being measured) by ensuring that when compared to a steel rule, the allowable slop is within your established limits. The rest of the tape should remain consistent, barring any kinks or bends.

Regarding the tape measure, if I have a tolerance of +/- 1/8 inch, does that mean that I must be able to read the measurement to +/- 0.0125" if the measurement appears on my control plan but is not a customer designated key (special) characteristic? Also what about conversions from metric to English? As an example, say the spec for the thickness of material is 1+/- 0.1 mm; this would convert to (approx.) 0.03927+/-0.003927. How would this be handled best?

I have been involved in a debate around the "unique Identification" of tape measures used to accept and reject product. Most areas of our facility assign a number to "each piece" of IMTE and have a gage card matched to each piece as evidence of verification. Excellent work! One department has chosen to affix a verification sticker to each piece, but all IMTE verified in the same month all have the same sticker. No way to tell them apart and no gage card for each piece. All tapes appear identical. The only record is a list of operators and a check mark beside their name if they received a tape that particular month. I do not see a "unique identification" here. Am I missing something? Can tape measures be lumped into a category as one peice of equipment? HELP

IMHO if each of the M&TE are NOT distinguishable in some way (serial number, colour, or equivalent), the 'unique' requirement is NOT being met.

[This message has been edited by Marc Smith (edited 19 August 1999).]

SR,

Converting English measure into metric often leads to errors. We are a 'metric' only organization and to avoid errors, we consistently measure and test in metric units. My suggestion: do not convert.

A majority of the time when we do have issues of conversion, they arise in the supplier arena. Often time, first piece inspections submitted are converted into English measure, and I can count on at least a few conversion errors.

Just a passing thought, so back to the group...

Regards,

Kevin

SRTipton-
Typically, if it is on the control plan, it is important, and being controlled.

From my limited experience, most methods of measurement dictate [roughly] adding another decimal to the readings. There are digital calipers, for instance, that read to 2 places. A part of 19 +/- .02 that measures 19.023 will read 19.02. The part is out of spec and you will accept it. At least the measurement device should distinguish .001 increments.

Without knowing your requirement, I suggest that if it is worth controlling, it is worth measuring correctly.

And I use .03937 to convert. See? As Kevin says, avoid converting.

Yeah - the 'old' rule of 10!

I have a cert from "Starrett" for a 12' tape purchased in 1997 that provides all the required info;
Guide 25 certified
dimensional verification
hook error
uncertainty
95%cl
plus specifications and procedures.
They are available, you just have to go to the right source.

There is still the "calibration" versus "verification" issue. Regarding "verification" of tape measure (agreed- you can't calibrate as you can't adjust to nominal) must be done at least once. And must be redone periodically to check for play on the end clip and legibility of graticules/increementation.

However, one point did not seem to come up. If you have an initial certificate of traceability with uncertainty, etc from the manufacturer, that is one thing. But I have seen quite often on tape measures that one does not exist. So the accuracy of the tape measure must be measured. In my old days as a contractor metrologist, I have seen tape measures out-of-tolerance. They did not meet original manufacturers specs for length accuracy (we tested on a surface plate with either gage blocks or a metrology grade straight edge ruler, a variety of increment lengths and at various points along the length of the tape). There are some military verification procedures that specify this method.

Akso see:
http://Elsmar.com/ubb/Forum4/HTML/000097.html
and http://Elsmar.com/ubb/Forum4/HTML/000130.html
and http://Elsmar.com/ubb/Forum4/HTML/000170.html

Calibrating a tape measure is a good idea. It is such a commonly used tool like a square or a level. It should be accurate. We found that even new tape measures could be off 1/16 of an inch. It would be nice to know this before you bought a new tape measure. It's really nice to be able to keep a tape measure accurate for many years. Lixer Tools makes a tape measure calibrator which addresses all of this. With this tool you can verify the accuracy of both the push and the pull measurements of your tape measure. You can easily adjust a bent end hook to restore accuracy or determine if the rivets may be worn beyond your required range of accuracy. In this case, it is time to replace the tape measure. In order for any measuring to be meaningful, you must know what your required range of accuracy is. In some cases, a tape measure simply can't conform to the accuracy requirements.

Calibrating a tape measure is a good idea. It is such a commonly used tool like a square or a level. It should be accurate. We found that even new tape measures could be off 1/16 of an inch. It would be nice to know this before you bought a new tape measure. It's really nice to be able to keep a tape measure accurate for many years. Lixer Tools makes a tape measure calibrator which addresses all of this. With this tool you can verify the accuracy of both the push and the pull measurements of your tape measure. You can easily adjust a bent end hook to restore accuracy or determine if the rivets may be worn beyond your required range of accuracy. In this case, it is time to replace the tape measure. In order for any measuring to be meaningful, you must know what your required range of accuracy is. In some cases, a tape measure simply can't conform to the accuracy requirements.

Doug,

Welcome to The Cove Forums! :agree1: :agree1:

You are recommending a particular device for tape measure calibration.
Are you associated with this organization? Please look at the TOS (http://elsmar.com/Forums/showthread.php?t=8831), Article 3b.

Stijloor.

This is a tool we invented about 20 years ago to use in our custom cabinet shop. We have recently applied for patent protection. It has been a very useful tool to keep our shop calibrated. I always thought that somebody must have already invented this tool. In searching for similar tools, we encounter forums and discussions such as yours. We wish to share our tool with others as clearly there is a need to calibrate tape measures.

I was surprised to see this calibration tool made of wood. Looks nifty, but we end up with a problem of traceability (that is, a lack of).

I was surprised to see this calibration tool made of wood. Looks nifty, but we end up with a problem of traceability (that is, a lack of).
Thanks for the input! Yes, ultimately, all calibration (and corresponding "certification of the calibration") does need to be traceable to NIST Standards. Without such traceability (and periodic recalibration/recertification of the instrument used in calibration), the instrument just becomes "an interesting gadget for seat of the pants tuneup for tape measures" (kind of like a mechanic estimating an engine speed by ear instead of using a calibrated/certified tachometer.)

Thank you for your input regarding the Lixer tape measure calibration tool.
We have researched and tested this simple tool in our shop for 20 years. Some of the interesting facts that I might point out would be that a common new tape measure from Stanley, Starrett, Craftsman, Lufkin, etc. are not perfectly accurate. Their manufacturing standards target a range of accuracy that might be +/- 1/32". Some of the more generic types of tape measures have a hard time keeping their tolerance within 1/16". As we compared various brands of tape measures and steel adhesive backed rules for our saw fences etc. we found unacceptable differences between many of the above listed. With the help of a Lixer, we are able to identify problems, make adjustments, and adhere to a reasonable shop standard. We tend to use 12' Lufkin tape measures as we have found that these are consistently more accurate. (We have no relationship to Cooper Tools).

To specifically address your concerns, I will reference information from The Engineering ToolBox Coefficients of Linear Expansion and make note of specific linear temperature expansion coefficients of the following:

ABS Glass fiber reinforced 17
Aluminum 12.3
Titanium 4.8
Wood, oak parallel to grain 2.7

Wood has a very acceptable factor of stability for this application.

We have also done a 8 hour submersion test on wood. We found the linear expansion to be minimal. To do this test, we started with a 5" long block of maple at less than 6% moisture content. We soaked the block of maple in water for 8 hours. We trimmed approximately 1/4" off of each end and measured the length of our test piece of wood at 4.493". Our moisture test indicated excess of 20% moisture. That is as far as our scale would read. We periodically tested for moisture and allowed the piece of wood to air dry. When the moisture level reached 6% again, the length measured at 4.492". For us, this was very acceptable.

Other obvious benefits of the wood may be that it is non-conductive and when you drop it, it is not likely to bend. And for those that care, it is environmentally friendly.

Our difficulty in producing this tool was addressing the issue of accuracy. We have felt from the beginning, that this is the most important factor. Without this tool being accurate, it really isn't worth anything. We offer as part of our warranty, to calibrate specifically and indicate errors within the +/-.002 range which we guarantee. We individually inspect every Lixer. Under magnification, we compare each laser engraved alignment mark to a precision ground standard.

We feel that in most applications a Lixer will narrow your range of accuracy from "who knows what" to +/- .002. In order for any measuring to be meaningful, you must know what your required range of accuracy is. In some cases, a tape measure simply can't conform to the accuracy requirements.

This is what has been accepted by all regulatiory auditing bodies for my company since 1998 and we so Sefense Contracting among many other such jobs.
Text from my Work Instruction:
"· Measuring tapes will be used for measurements in production and quality when the applicable tolerance is 1/16” or more; for tighter tolerances a more accurate measuring device shall be utilized.
· No tape measure without the verification tag may be used in manufacturing or quality without having been accepted and processed by these requirements.

· The Tool Crib Attendant issuing Tape Measures will verify the accuracy prior to issue. This requirement also applies to personal property used in manufacturing. It must be entered into the control system by taking to the tool crib attendant for verification.

· This verification is made by comparing the painted dimensional increments on the tape to a known measurement to within 1/32” accuracy. A 48” Metal Scale that has been verified as accurate is used.

· The initial verification will be recorded on form QA 103 at time of issue by the issuing personnel. Once verified as accurate, the tape measure will be affixed with a tag showing the number assigned it, the date it was checked, and by whom. Since metal tape measures are not adjustable, no due date is applicable, only replacement of the tape when accuracy is no longer acceptable.

· After initial issue, personnel using tape measures are responsible for performing the verification of accuracy.

· Tape measure users are responsible for inspecting their tapes to assure that {1}no damage has occurred to the end hook that may interfere with accuracy; {2} painted lines & increments are readable and metal tape is not damaged by cuts, bends, crimps that may affect accuracy.
· Further verification, any time the accuracy is in question, may be done by comparing the tape with one of three Metal Scales that are located at the following sites:
· Tool Crib issue
· On the aisle side of the Paint Booth
· On the end of the horizontal tool rack in the Bellows Dept.
· Should any problems exist concerning tape measures and their verification, Quality Assurance will be notified to evaluate the situation.":agree: