Tape Measures & Scales - Part Tolerance - Gage R&R

[Linda Miller]

Tape Measures & Scales

There is some controversy regarding the necessity to perform R&R on items like tape measures, scales etc. The spec states that all items listed on the control plan must be calibrated.

But items like tape measures and scales seem silly do perform R&R, the gauge does not change it is all operator dependant.

Can anyone shed some light on this for me? I feel like this is not necessary, but is it a requirement and if so, how would the calibration or R&R be performed??

 

[Atul Khandekar]

R&R is not just about the gages. Its also about variation due to operators, envirnment, methods - the whole system. In your case, you already know that there is variation due to operators. If the characteristics you measure are critical, you need to reduce this variation. R&R exercise will help identify sources / causes of variation, so you can take proper action where necessary. You can also ask your customer if they need R&R done on the tape measures & scales.

If you search the forums for 'Tape Measure' and I am sure you will find many threads discussing calibration requirements of tape measures.

 

[Marc]

We're talking QS-9000 or TS 16949, I assume?

R&R = Repeatability and Reproducability

(broken link removed)

The repeatability test is a simple demonstration of the capability of a gage to perform a required task with the degree of "uncertainty" being less than the tolerance band allowed for the process. For example: If you have a callout of .010 - .014mm you would want to make sure that the gage (and the operator) were capable of reading a consistent number within the tolerance band. Generally 10% or less variation is acceptable, 10-30% is tolerable if you have efforts toimprove the situation, and above 30% is inpermissible, you must STOP. The reason for this guidline is to prevent operator (or gage) errors from corrupting the gage measurement process.

Say, you take 10 parts and measure them and record the information in a table. You repeat the measurements. Ideally each time you read a certain dimension you would get EXACTLY the same number. This is the "Repeatability" of the "R and R" study. Then a second person, using the same gage and same ten parts measures the parts, again n times. Next, a third person does the same. By comparing the results of three people you now have the "Reproducibility" portion of the "R and R" study.

 

[Atul Khandekar]

That's right!

You may also refer to AIAG's MSA Manual that gives very detailed procedure and calculations for conducting R&R studies.

 

[Atul Khandekar]

Re: Tape Measures & Scales

Linda Miller said:

There is some controversy regarding the necessity to perform R&R on items like tape measures, scales etc. The spec states that all items listed on the control plan must be calibrated.

But items like tape measures and scales seem silly do perform R&R, the gauge does not change it is all operator dependant.

Can anyone shed some light on this for me? I feel like this is not necessary, but is it a requirement and if so, how would the calibration or R&R be performed??

In reply to a question in this thread, Martin Greenaway drew my attention to the following (p23 - MSA Manual)

"...The type, complexity and purpose of a measurement system may drive various levels of program management, strategic planning, measurement systems analysis or other special considerations for measurement selection, assessment and control. Simple measuring tools and devices (i.e., scales, measuring tapes, fixed-limit or attribute gages) may not require of management, planning, or analysis that more complex or critical measuring systems demand.... The decision as to the appropriate level shall be left to the APQP team assigned to the measurement process and customer. ..."

 

[Linda Miller]

Re: Re: Tape Measures & Scales

Thank-you, this makes more sense to me. I appreciate the help.

 

[Laura M]

Tape measure calibration

Anyone familiar with crane/hoist chain inspection for wear in which a specified number of links is supposed to be no greater than X-inches? My client uses a device to "stretch" the specified number of links then measures the length with a tape measure. I'm thinking at this point I found a situation where tape measures need to be calibrated. Comments? (Manufactures recommendations is to purchase a go/no go gage from them, however client developed tool to get an actualy measurement,

 

[SteelMaiden]

FWIW -
You cannot "calibrate" a tape measure, but you can verify its accuracy. We just had the registrar here and there was some discussion about why we didn't put serial numbers, calibration stickers, etc., on the tape measures. Basically, we argued (successfully) that we did a verification and logged it, that the tape was OK at the beginning of shift. If the tape is not OK, we cut the end off so it cannot be used, and throw it away.

As for GRR, if your measurements are critical, sure, why not. But, what we are doing is not nuclear physics, so we just really don't find any value in it. If your tolerances are measured in inches or even feet what is the point? (all our real measurements are done in-line using laser or other technology, so tapes are basically just a verification).

What we want to do is to track our tape life. Is there any trending toward operators?, or are there areas in the plant where tapes don't last as long? Our goal is to reduce the verification frequency where possible while maintaining accuracy.

My pet peeve is the registrar's auditor coming in and asking about in-house tape measure calibration - if someone here discovers a way to adjust tape measures, let me know OK?

 

[tomvehoski]

As for verification/calibration of tapes, I have claimed the need to be and don't need to be depending on the application.

For a welding shop that made bases for machines, I implemented a verification system to check the tape against a calibrated block. My thinking was that if they did have a bad tape and mounting holes ended up 1/4 inch off, there was a possiblity the customer would have a problem when mounting the machine.

For a trade show display manufacturer we do not verify. The test of quality is if everything goes together, and they assemble the display so the customer is not concerned how accurate the measurements are, just that it looks good.

If you do verify and dispose of tapes often, look at buying from Sears. I have had several places tell me Sears replaces them for free no matter how abused.

Tom

 

[Angela-2007]

Questions-

We utilize packaging scales. The auditors have told us that they need to be calibrated. They are only utilized to weight the packaged part for shipping purposes. Can anyone think of any reason that they would need to be calibrated?

Angela