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Do length standards grow over time ?

I never quite understood this. If you're going to do something non-compliant with the standard to intentionally fudge the numbers, why not just pencil whip it and be done?
Of course I wasn't there and the toolmaker is long gone so it's speculation.

What it sounds like to me is a feud between the toolroom and the engineering department. Some tight-assed engineer applies tolerances that are so tight they're hard to meet, and the toolmakers know that they're not functional, either for tool operation or for the finished product. But they have enough integrity they don't want to write down something completely fictitious on the inspection sheet. So they can say with absolute honesty that they measured that feature and got that number on the mic.
 
Of course I wasn't there and the toolmaker is long gone so it's speculation.

What it sounds like to me is a feud between the toolroom and the engineering department. Some tight-assed engineer applies tolerances that are so tight they're hard to meet, and the toolmakers know that they're not functional, either for tool operation or for the finished product. But they have enough integrity they don't want to write down something completely fictitious on the inspection sheet. So they can say with absolute honesty that they measured that feature and got that number on the mic.


My interpretation of the story was that the toolroom people and the inspection people were not one in the same, and the inspection people may or may not have even known the gig?


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I am Ox and I approve this post!
 
My interpretation of the story was that the toolroom people and the inspection people were not one in the same, and the inspection people may or may not have even known the gig?


-----------------

I am Ox and I approve this post!
Yes. The company no doubt had inspection people for the finished product (pens) but the toolmakers disassembled and checked new tooling when it came in before they even ran first-piece.
 
The old measure it until it checks right.
If you measure something again and again you will get different numbers. It is just Gage R&R.
Knowing this what can you trust the measuring to?
I've seen five checks say bad and the sixth says in. Okay, good part.
Or the other side have seen inspection is not happy the parts are jobbed out. Things towards the edge and measure until it and the batch fails.
So there is a whole inspection world deal of type one and type two errors.
And then the silly world of CPK, CPA..etc. Of course these people are nuts and looney... maybe
There is this I do not know for sure the range or question. One needs to know that range for any measuring and make sure you are always inside it.
Here is the bad. This means all print tolerances need to be reduced by your uncertainly. Obviously that is not a well liked idea.
It is a can of worms.
Bob
 
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A couple of my amateurish thoughts about length standards.
The big problem with these blocks is that they cannot be made from classic materials that retain their dimensions well over decades and/or have a low coefficient of linear expansion. But they cannot be made from such materials because the length standards must have very high wear resistance. Practically, the choice comes from steel, carbide and ceramic - the latter is best, but the cost makes me sad.
A good example of where there is no problem of wear resistance is metal line rulers, like those that were installed on precision coordinate machines before the advent of induction rulers. These are sticks with strokes at some distance. Usually they were made from “precision alloys” such as Invar, in two versions - either with thermal expansion like steel, or with thermal expansion close to zero. But these are very soft alloys with poor wear resistance, which unfortunately are not applicable for length standards.
 
Do length standards grow over time ?
I recently sent for certification 2 very old length standards,. a 1" and a 2".
Made by Pratt and Whitney, Nice velvet lined wooden box.
In excellent shape. I assumed because of their age and wear they would be on the minus side.
Both were long, the 1 " was .00007 over and the 2" was .00017 over, almost 2 tenths.
They were just certified for a friend and wont be used, just done for the knowledge of the actual size.
Thoughts about why they are long, made that way or did they grow ?
I have seen these types of results more than once. Every time the calibration lab couldn't measure. Don't get me started on calibration labs. Just this year I dealt with several labs that were certifying measurement equipment with a TUR under 1.........
 
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