Temperature Requirements For In House Calibration - AS9100

[Kronos147]

...checking a pair of 6" calipers with with a stated accuracy of ±.001", we would check the caliper against the gauge blocks at every inch within its range to verify that it is reading the value of the gauge block ±.001" (e.g., 1" ± .001", 2" ± .001, etc.). However, based off of the quote above, it sounds like we would have to do a lot more. Is this the case?

There are four ways to measure with the calipers. Your records will need to reflect you checked all four features.

 

[Tyler]

There are four ways to measure with the calipers. Your records will need to reflect you checked all four features.

Right. Thank you.

 

[Ninja]

My naive assumption is that we could buy highly accurate gauge blocks, something like this gauge block set, and use them to verify that our devices are reading within their stated accuracy. For example, if checking a pair of 6" calipers with with a stated accuracy of ±.001", we would check the caliper against the gauge blocks at every inch within its range to verify that it is reading the value of the gauge block ±.001" (e.g., 1" ± .001", 2" ± .001, etc.). However, based off of the quote above, it sounds like we would have to do a lot more. Is this the case?

To flesh out another aspect:
How do you know the gage blocks are accurate? They need calibration/verification too. They are a gage.

Back to the thread title: Is there any chance in the world that thermal variation would impact a +/-0.001" tolerance on 6" calipers or or a 6" gage block? I think not.

 

[Tyler]

How do you know the gage blocks are accurate? They need calibration/verification too. They are a gage.

The gauge blocks would be verified by an accredited third party lab. We still believe this would be cheaper than having all of our calipers and micrometers checked every 6 months.

Back to the thread title: Is there any chance in the world that thermal variation would impact a +/-0.001" tolerance on 6" calipers or or a 6" gage block? I think not.

Based on the excel spreadsheet I made, it does not look like an accuracy of ±.001" would be a problem; but it may be for an accuracy of ±.0001". Again, I am not a metrologist, so I am not entirely sure if the way that I went about analyzing the uncertainty with respect to temperature and length is correct.

 

[Ninja]

My math:

TCE of carbon steel ~ 11ppm/degK (The product description says "Blocks are high-carbon, high-chrome steel and have excellent stability and resistance to thermal expansion. "...so figure that TCE is actually much lower.
note that degC and degK are the same for this usage.

11ppm = 11 millionths per inch per degK
11 / 1,000,000 * 6 inches = 0.000066 inch expansion per degK.
For a 10degC change in temp (HUGE), the biggest block will expand 0.0006...and you'll be sweating profusely or wearing your winter coat.
For a 5degC swing, 0.0003.
...and that's on the largest size. One sixth of that for the 1" block.
...and this is intentionally overstating TCE to basic carbon steel instead of {whatever the description means}.

In anywhere I've ever worked, we'd let the workers go if the temperature swung 5degC...none of our other processes would function.

HTH

...oh, and while you're at this...it's (always) worth revisiting whether the 6mnths is justified...when's the last time a gage failed check?

 

[Tyler]

...oh, and while you're at this...it's (always) worth revisiting whether the 6mnths is justified...when's the last time a gage failed check?

We have never had a gauge reported as out of tolerance after calibration/verification.

 

[Ninja]

We still believe this would be cheaper than having all of our calipers and micrometers checked every 6 months.

We have never had a gauge reported as out of tolerance after calibration/verification.

Off the original topic...but based on this I would consider moving the cal cycle to a year...with a "revisit" in a couple years to see if it should be moved to 18mnths or 2yrs.
Money is money.