Calibrating or Verifying Metal or Steel Tape Measures

jonerenberg said:

I have a question of calibrating steel rules. We have a procedure where we compare it against a micro-vu measuring system. However, I am trying to figure out what tolerance is acceptable. Any thoughts

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What is the tolerance of the characteristics you are going to use it for? It should be 4:1 to 10:1 (depending on who you listen to) of your minimum required resolution. So, if you are measuring something +/- .5 inches (tolerance 1.00 inches), your resolution should be approximately .1 inches (10:1) and your calibration tolerance should be .025 (4:1) to .01 (10:1) inches.

Re: Calibrating Tape Measures

ScottK said:

I'm with the "for reference" crowd.
A tape measure is not a precision instrument.

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I'm all for labeling tapes "for reference only", but if they are used to accept or reject product, is this still valid ?

Re: Calibrating Tape Measures

jguns said:

I'm all for labeling tapes "for reference only", but if they are used to accept or reject product, is this still valid ?

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I think the statement answers itself. It is no longer for reference only.

Re: Calibrating Tape Measures

jguns said:

I'm all for labeling tapes "for reference only", but if they are used to accept or reject product, is this still valid ?

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bobdoering said:

I think the statement answers itself. It is no longer for reference only.

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Which in and of itself doesn't answer the question, and points out one of the reasons that "for reference only" is silly. ISO 9001:2008, 7.6 says that calibration or verification must be done "[w]hen necessary to ensure valid results ..." If calibration isn't necessary to ensure valid results, there's no good reason to do it, and no good reason to put "reference" stickers on things. You just need to be able to justify the decision.

Re: Calibrating Tape Measures

ScottK said:

I'm with the "for reference" crowd.
A tape measure is not a precision instrument.

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That is an interesting criteria.

Re: Calibrating Tape Measures

Jim Wynne said:

...You just need to be able to justify the decision.

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Yes, there is the fun part. Let the games begin. If it wasn't for this, we wouldn't need screen printed pocket scales or trade show plastic calipers.

Now, if you step out of ISO 9001:2008 quality level TCE and step into ISO/TS 16949:2009, the criteria is a little more specific:

7.6.2 Calibration/verification records
Records of the calibration/verification activity for all gauges, measuring and test equipment, needed to provide evidence of conformity of product to determined requirements...

So, sure, if you are a minimalist you will not see the sense in that...but somebody did...and there it is. If you quality system is TCE and not ISO/TS 16949, then you are pretty much free to do whatever you can "justify".

Re: Calibrating Tape Measures

jguns said:

I'm all for labeling tapes "for reference only", but if they are used to accept or reject product, is this still valid ?

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Then it should be verified according to it's need.

The process must work. People should know (or be able to easily find out) what equipment/instrumentation is appropriate for their task. Obviously the flip side is that they know what equipment is not to be used for a particular application. That may involve for reference only stickers, color codes, containers, posted equipment lists, etc., etc. There are a number of ways to approach it. So as long as everyone in the organization is on board, and valid results are being produced.

Friends,

I feel haunted by tape measures.....



Stijloor.

Re: Calibrating Tape Measures

Jim Wynne said:

Which in and of itself doesn't answer the question, and points out one of the reasons that "for reference only" is silly. ISO 9001:2008, 7.6 says that calibration or verification must be done "[w]hen necessary to ensure valid results ..." If calibration isn't necessary to ensure valid results, there's no good reason to do it, and no good reason to put "reference" stickers on things. You just need to be able to justify the decision.

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Ok guys.. so what do y'all recommend ? Currently, we "review" our tapes every 6 months for wear, etc.. and found that it's cheaper to just replace those that obviously need it. But if they still look decent, how do you recommend "calibrating" a 25' tape ?

Re: Calibrating Tape Measures

jguns said:

Ok guys.. so what do y'all recommend ? Currently, we "review" our tapes every 6 months for wear, etc.. and found that it's cheaper to just replace those that obviously need it. But if they still look decent, how do you recommend "calibrating" a 25' tape ?

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Actually, you are probably in good shape. If you have a long gage block - 4" or so, you might want to see if it measures within the accuracy you need for the tightest tolerance you measure. Look for any particular wear in the areas of the tape measure you actually use. The most error comes from the tape hook. Replacement is your best action for tapes that are no longer accurate enough. Hardly worth riveting on new hooks.... Some places with many tapes use one calibrated tape to verify the other tapes. That gives you a standard to verify linearity, if necessary.

If you need to do more than that, it may be the wrong gage for the job.