Feels like a chicken and egg senario. Let’s say I get my torque wrench from work sent off to be calibrated, and that’s calibrated with something itself needs to be calibrated, and so on and so fourth. How’s that figured out?
In: 430
I happen to know of a textbook that covers this exact topic: [Foundations of Mechanical Accuracy](https://archive.org/details/FoundationsOfMechanicalAccuracy). It’s actually quite complex when you get down to it, but the other comments have it essentially right. You need a “Master” calibration tool that is more precise than all the rest of your tools which you can measure against. The book goes into detail on how you can create some of these master tools.
For instance, how do you create a perfectly flat plane from scratch (or as near perfect as can be)? If you already have a master flat plane to measure against, it’s easy — all you do is push your plane against the master and see where they aren’t touching evenly (dye can be used to make this more clear). Once you know where they aren’t touching flat, you can sand your plate down until it does. But how do you make a master plane without a master to reference?
The trick is to make three different flat plates and compare them to each other. Call them A, B, and C. Put A and B together, then sand them down repeatedly until they lie flat against each other, even when rotated 90/180 degrees. They’ll be *mostly* flat, but you can’t be sure that one doesn’t have a depression and the other a bulge. So what you do next is sand down C until it meshes with A. Since B and C both mesh with A, they’ll both have the same bulge or depression. Now you can mesh them with *each other*, and sand both down to get rid of that bulge/depression. If you keep repeating this process alternating between A, B, and C, eventually all three plates will lie flat against each other, and you can be confident that they’re all near-perfectly flat.
Each kind of master requires different tricks like this, but they all boil down to the same idea – gradually calibrate multiple different master versions against each other until they all agree with each other.
Feels like a chicken and egg senario. Let’s say I get my torque wrench from work sent off to be calibrated, and that’s calibrated with something itself needs to be calibrated, and so on and so fourth. How’s that figured out?
In: 430
I happen to know of a textbook that covers this exact topic: [Foundations of Mechanical Accuracy](https://archive.org/details/FoundationsOfMechanicalAccuracy). It’s actually quite complex when you get down to it, but the other comments have it essentially right. You need a “Master” calibration tool that is more precise than all the rest of your tools which you can measure against. The book goes into detail on how you can create some of these master tools.
For instance, how do you create a perfectly flat plane from scratch (or as near perfect as can be)? If you already have a master flat plane to measure against, it’s easy — all you do is push your plane against the master and see where they aren’t touching evenly (dye can be used to make this more clear). Once you know where they aren’t touching flat, you can sand your plate down until it does. But how do you make a master plane without a master to reference?
The trick is to make three different flat plates and compare them to each other. Call them A, B, and C. Put A and B together, then sand them down repeatedly until they lie flat against each other, even when rotated 90/180 degrees. They’ll be *mostly* flat, but you can’t be sure that one doesn’t have a depression and the other a bulge. So what you do next is sand down C until it meshes with A. Since B and C both mesh with A, they’ll both have the same bulge or depression. Now you can mesh them with *each other*, and sand both down to get rid of that bulge/depression. If you keep repeating this process alternating between A, B, and C, eventually all three plates will lie flat against each other, and you can be confident that they’re all near-perfectly flat.
Each kind of master requires different tricks like this, but they all boil down to the same idea – gradually calibrate multiple different master versions against each other until they all agree with each other.
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