Circularity tolerance of 0.25mm - The correct Go/NoGo gauge size

[r1daveg]

My first post here, so a "hello" to you all.

I have a customer drawing which calls for a diameter of 80+/-0.095, but also has a circularity tolerance of 0.25mm.

What would be the correct Go/NoGo gauge size? (Old drg - not GD@T)

[Jim Wynne]

In Reply to Parent Post by r1daveg

My first post here, so a "hello" to you all.

And hello to you too, and welcome.

In Reply to Parent Post by r1daveg

I have a customer drawing which calls for a diameter of 80+/-0.095, but also has a circularity tolerance of 0.25mm.

What would be the correct Go/NoGo gauge size? (Old drg - not GD@T)

You can't measure circularity with a plug gage, so you should probably use a bore gage, which will tell you something about the shape of the hole in addition to the size.

[r1daveg]

Thanks for your reply Jim.
I omitted some "vital" info...
Its an internal size, based on 8 flats.

[Jim Wynne]

In Reply to Parent Post by r1daveg

Thanks for your reply Jim.
I omitted some "vital" info...
Its an internal size, based on 8 flats.

Now you've lost me, I'm afraid. What does "based on 8 flats" mean?

[r1daveg]

It's an octagonal shape, so the diameter is a "minimum material" size.

[silentrunning]

In Reply to Parent Post by r1daveg

It's an octagonal shape, so the diameter is a "minimum material" size.

Welcome.

If you have an Octagon, you can't have a diameter. A diameter is used to measure a circle or arc. An octagon is made up of 8 equal straight lines. If your customer is talking "effective" diameter that would be a different matter. But then, I don't understand the circularity tolerance. Hmmmmm?

Doug

[Jim Wynne]

In Reply to Parent Post by r1daveg

It's an octagonal shape, so the diameter is a "minimum material" size.

I'm with silentrunning on this one. How can you measure the circularity of an octagon? Have you discussed this with the customer? If not, you should, especially since your original post indicates that you're not sure about how to gage the feature. Ask them how they do it.