Checking Diameter at Specific Spot.

[[Mi...]]

I've been requested to verify some measurements.

I'm given parts with a bore they measured using an air gauge, just a 2 point measurement.

They want me to replicate that on the CMM, but that's not something I've done as that's a pretty useless way to measure diameter. I don't see an easy way in Calypso to do it exactly. I could manually probe points and get a distance that way....

Any ideas? am I overthinking this?

[[Da...]]

In Size\Standards there is a 2 point diameter function. I agree with you that a full circle would give a more accurate result of the diameter being checked. This method (in my opinion) can let bad parts go as good, simply because the points taken were at the narrow side of an out of round hole or boss. I don't use the 2 point diameter, but, if the engineer insists then it is on them.

[[Mi...]]

Thank you I had to look at a newer software version to see that, I'm mostly stuck in the dark ages on version 4.0.

I have to look up how to use it but it looks like the With Evaluation Range option is what I want, just not sure what the angle is in relation to, onto the hopefully useful help files!

[[SH...]]

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4.0!! Too old, l think lot of changes passed.

[[Ow...]]

If possible, it’s a good idea to measure the master they’re using to set the air gauge to and if you don’t get the same size and near perfect roundness on the master, you know to make adjustments, filters, speed, temperature, etc.

Along with the two point diameter, you should report roundness with a plot to show the highs and low’s. A two-point air gauge will not give accurate roundness results on a part with unequally spaced highs and low’s (most machining operations do have equal as long as distortion is not involved) and a 3 point air gauge should be used. Reporting roundness will show why you may be getting a different result than they are.

[[Mi...]]

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That's next step, the results I got using the 2 point measurement on the same locations were all slightly larger than theirs.

Thanks all!

[[Ke...]]

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I recently had an engineer (no longer with the company) telling the SQE's that "air gages are more accurate than a CMM"
I had to explain to the SQE that an air gages are set to masters with very tight size/roundness conditions, and that as parts being measured deviate from nominal roundness conditions, the accuracy of the air gage results diminishes. While still trying to assure them that they are good as an in-process check (SPC)... anything I missed?