Max Inscribed Vs Max Circumscribed

[[Ma...]]

what is the difference on how max inscribed and min circumscribed is calculated?

does it takt three inner points for Inscribed?

does it take three most outer points for circumscribed?

what is the difference on how it calculates it for a circle vs a cylinder?

[[Ma...]]

It should be 3 points for circle and 5 points for cylinder.

[[Da...]]

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If you follow the standards to the dot, then this is not true anymore.

In ISO, tangential elements are based upon Chebycheff (also called Min-Max) elements shifted to the highest contact point, in ASME they're based upon Gaussian elements, also shifted to the highest contact point. This method leads to more stable tangential elements, especially for planes in a rocking situation.

In many situations the resulting elements are virtually indistinguishable from the three-point contact elements.

[[Da...]]

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Do you know if Calypso 2023 with its beta GD&T magic can actually follow the standards with ease?

[[Da...]]

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I didn't get a chance to test it, but Zeiss claims that it does. You should be able to easily test it yourself, just measure a tangential cylinder with the old math and the new math, and then use the points of the cylinder to construct a Min-Max (Chebycheff) or Gauss cylinder and compare the coordinates and directions to each other (with a lot of decimals).

[[Ma...]]

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Thanks for info - i thought it's much simpler 🤣
But if we go beyond calculations and stuff, then for circle it should be 3 points as minimum and 5 for cylinder right?

[[Da...]]

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Correct.

[[Ma...]]

Thank you much appreciated.

[[Ni...]]

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The main difference is that for IDs,
the Maximum Inscribed gives you the smallest Diameter it can find.
Minimum Circumscribed gives you the biggest Diameter it can find.

For ODs,
the Maximum Inscribed gives you the smallest Diameter it can find.
Minimum Circumscribed gives you the biggest Diameter it can find.

The diameter that it finds is based on roundness too. The worse the roundness, the bigger the difference it is when you apply the evaluation.

[[To...]]

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😉

[[Da...]]

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:)

[[Je...]]

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This was a very keen observation, Daniel. Thanks for highlighting it.

I actually had a discussion with one my team members about this last week. He's a PC-DMIS programmer, so it was interesting to compare how the two software establish features and boundary zones.

[[Je...]]

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Also, the following resource has been posted on this forum a number of times, and I find it helpful. I forward it to engineers and other stakeholders regularly. Per Daniel's comments, a few things in this document could be updated to more closely voice ISO / ASME, but I still find it extremely useful.

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[[Ky...]]

Hello all,

There is a lot of good information in here. I just wanted to point out that there is a document in our knowledge base that covers not only the difference between max inscribed/min circumscribed, but also several other options as well.

https://portal.zeiss.com/knowledge-base?id=420544

Hope this proves helpful.

[[Je...]]

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Kyle, thank you very much for pointing us to this.

Btw, you are a rockstar Application Specialist who has helped me out more times than I can count (at least with my current PiWeb license ⚡😏).

Thanks for contributing here, and please do so as often as you can.

[[Je...]]

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Mateusz! I didn't recognize you at first. How's it going? You should stop by Cretex sometime, or perhaps we could meet for lunch and talk shop sometime.