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Roundness vs Surface Profile


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Technically Roundness is a single cross-section. Surface Profile would apply to the surface. The Surface Profile is most likely also taking into account the diameter.
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I didn't say that Roundness takes size into account, I said that most likely the Surface Profile does though, especially if it is a closed loop.
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I told you I wasn't thinking clearly.... Thank you.

Richard, I understand that we typically think of roundness being applied to a single circle section but Calypso allows you to select a cylinder and a sphere. When I have applied roundness to a cylinder, I happen to get the same number as the cylindricity. I assume the same would apply on a sphere and sphericity. Don't know. Haven't tried it. YET.
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Roundness tolerance applies to ANY circular section of an element. If you apply a roundness characteristic a feature with multiple circular sections in Calypso, it outputs the total form error as a result. Each circular section needs to be evaluated separately for roundness and the greatest deviation should be compared to the tolerance.
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If roundness is applied to a cylinder and is within the specified tolerance, then any of the circular sections would automatically be within the roundness spec.
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It is true Tom, that if a roundness tolerance is applied to a cylinder in Calypso an in spec. result would guarantee that all the circular sections were also in spec. The problem with this method would be that there are circumstances where you would reject good parts. For instance, a cylinder with a 0.1 mm size tolerance and a 0.005 mm roundness tolerance. If the part had all circular sections within tolerance but was tapered 0.025 Calypso would output the cylindricity error for roundness and fail the part.
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Yes, I agree. I wasn't advocating the use of roundness on a cylinder but just pointing out a particular condition exists. 😃
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Yes, I see your example. This phenomenon would occur if measured as individual circles. The measurement of the circular sections should be perpendicular to the axis, even if measured as individual circles.

Andreas, I have edited/deleted some of replies because I came to a better understanding of your drawing.
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