Gage Blocks

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ddickey

H-M Supporter - Gold Member
H-M Supporter Gold Member
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Apr 21, 2016
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Is the certificate of inspection an accurate report for import gage blocks?
 
I wouldn't bet the bank on it. Mike
 
A problem with gage blocks is that they can be stacked to build a required dimension and errors will stack as well. In order to be useful they have to be accurate to a degree beyond the metrology capabilities of the typical shop; measurements in the microinch range.

From a trusted manufacturer, a NIST traceable calibration would be sufficient to meet that requirement. In turn, an ISO 9000- or equivalent certification and subsequent CE marking should be sufficient to trust the manufacturer. However, unscrupulous manufacturers will slap a CE label on the product and a certificate of inspection may be nothing more than a glance at the product.

There is no way to know for sure that a set of gage blocks has passed the rigorous calibration required other than send them out for calibration to a certified metrology lab. You stand a better chance purchasing from a trusted vendor that states the set has been calibrated to NIST traceable standards and better yet provides a calibration report for each individual block.
 
Before you use ANY gage block from a Chinese set, measure it with an accurate micrometer to confirm the nominal size. It is common to find them mislabeled. They are useful, but don't assume anything. It really could happen with any gage block, regardless of brand, if it was made on a Monday morning or Friday quitting time made part. "Trust, but verify!"
 
It seems to me that the difference between a good gage block and a bad gage block is way less than a good micrometer can measure. My Mitutoyo has a resolution of 50 millionths, but the best class of gage blocks, .5, has a 1 microinch tolerance, and the "worst", 3, has a +8, -4 microinch tolerance.

In my shop I have no way of measuring this, so I'll have to trust or not trust the manufacturer. Fortunately, I have no need for accuracy anything near these levels. Yippee.
 
Winegrower said:
It seems to me that the difference between a good gage block and a bad gage block is way less than a good micrometer can measure. My Mitutoyo has a resolution of 50 millionths, but the best class of gage blocks, .5, has a 1 microinch tolerance, and the "worst", 3, has a +8, -4 microinch tolerance.

In my shop I have no way of measuring this, so I'll have to trust or not trust the manufacturer. Fortunately, I have no need for accuracy anything near these levels. Yippee.
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It is not the millionths of an inch accuracy that is in question here. What I am talking about is taking a decently accurate .101" gage block and marking it as .102" or .110", without making sure of the actual size. It is a not uncommon problem with low end gage blocks. With Chinese tooling, where quality assurance is widely skipped to meet a cost point, bad things can happen. Verify! Caveat Emptor!
 
Yes, I did see your point, Bob. That would be a gross error indeed.
 
Winegrower said:
Yes, I did see your point, Bob. That would be a gross error indeed.
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Yes, but not noticeable to the human eye, we take those numbers as gospel (not me, any more!) They are easy enough to test quickly with a micrometer to see if the label makes sense. Why ruin a fussy and long winded project due to lack of quality control and quality assurance by the gage block maker? I like to give them a quick test and then safely say TLAR (that looks about right.)
 
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