Countersink Concentricity

Our suppliers manufacture composite pannels that have 100° countersunk holes for fastener installation. We ask our suppliers to make shure that the countersinks are concentric with their holes within .002". Most of them drill and countersink in two different operations. How can they measure the concentricity of the countersink with their own pre-drilled holes?

I have seen the very instructive concentricity page from David Delong (see the 27th April 2011, 12:00 PM Comment in the Thread: Query on concentricity inspection).
I have seen several threads on this forum about concentricity...
But still, I don't get how to verify that.

Anybody has any clue?

Part of your confusion probably has to do with the fact that the general GD&T definition of concentricity is different from what you're actually looking for, which is true position. If your drawings specify concentricity for alignment of holes and c'sinks, they should be changed.

Jim Wynne said:

Part of your confusion probably has to do with the fact that the general GD&T definition of concentricity is different from what you're actually looking for, which is true position. If your drawings specify concentricity for alignment of holes and c'sinks, they should be changed.

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True - in the SME Tool and Manufacturing Engineers Handbook volume 4, incuding measurement to GD&T, explains that concentricity is really for rotating shafts, not a static dimension.

bobdoering said:

True - in the SME Tool and Manufacturing Engineers Handbook volume 4, incuding measurement to GD&T, explains that concentricity is really for rotating shafts, not a static dimension.

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It's not even very good for rotating shafts. In my personal experience, for rotating shafts concentricity on a drawing is intended as runout when clarified with the design engineer.

To check that particular feature will come down to what equipment you have available. If you are only going to check a small number (such as for a new project) you can use reprorubber and an optical comparator.

True Position said:

It's not even very good for rotating shafts. In my personal experience, for rotating shafts concentricity on a drawing is intended as runout when clarified with the design engineer.

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I don't think I've ever seen concentricity as a GD&T callout used correctly. Back in the old days, before CAD and GD&T, designers frequently used concentricity by its standard definition, when they wanted two or more circular features to share an axis. I think that might account for its misuse today, at least to some extent.

LouisLL said:

Our suppliers manufacture composite pannels that have 100° countersunk holes for fastener installation. We ask our suppliers to make shure that the countersinks are concentric with their holes within .002". Most of them drill and countersink in two different operations. How can they measure the concentricity of the countersink with their own pre-drilled holes?

I have seen the very instructive concentricity page from David Delong (see the 27th April 2011, 12:00 PM Comment in the Thread: Query on concentricity inspection).
I have seen several threads on this forum about concentricity...
But still, I don't get how to verify that.

Anybody has any clue?

Click to expand...

Do NOT use concentricity on countersunk or counterbored holes. One should use positional tolerances at MMC to the holes as a datum also at MMC. Now, to check the relationship. One would a 2 step cylindrical co-axial gauge with the smaller diameter the MMC size of the datum hole and the larger diameter of the gauge the virtual condition size of the positional tolerance.

Lets say we have a hole(s) of .250 +/- .005 while the counterbore is .600 +/- .007. We have a positional tolerance of a diametrical tolerance zone .008 at MMC with the datum (hole) at MMC.

Here is the gauge for the above. The smaller diameter is .245 (MMC size of hole) while the larger part is .585 (virtual condition size of counterbore - .600 - .007 - .008).

Simply insert the gauge in the hole until is bottoms out in the counterbore. If it does not bottom out in the counterbore, then it does not meet spec.