Verification of Charpy impact notch profile

[bhollands]

We break charpy "v" notch impact specimens. As part of the verification we check the notch profile on an optical comparator using an overlay that shows the allowable tolerance. The overlay is a gauge and therefore must be calibrated in some way, but I do not know how to have it done. Does anyone know where I can find a manufacturer that would make something like this or a way to calibrate it.

We have gotten go no-go gauges but these only check the notch depth and not the profile of the notch.

Bob

 

[metengr]

Review the information below, especially 9.2

http://www.boulder.nist.gov/div853/Publication files/NIST_IR6618_CVN_overview_procedures.pdf

 

[redpicker]

In my experience, it is the comparator that gets calibrated, not the overlay. The overlay can be verified, but if the comparator is calibrated, this can be done with the comparator itself. The overlay just simplifies the use of the comparator since you could verify the notch without the overlay, if you wanted to.

rp

 

[EdStainless]

Red is right on. You verify the magnification of the OC using NIST standards. Then you are in business.
We used to keep around a few NIST reference Charpy bars (the nice ground notch ones) to use as a quick verification that all was correct. After all you should have some around anyway. This was our operator check.

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Plymouth Tube

 

[bhollands]

Thank you for the response. We do have the comparator calibrated. Shouldn't the overlay be treated like any other gauge? We would never expect to have the overlay change but don't I need to have it checked that it has not changed and is still measures correctly? For example, we use a stage micrometer to check the brinnel scope. Unless there is obvious damage it should never change but we are still required to have it checked at a given interval.

Bob