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Haha. Just went through this last week.
https://www.pcdmisforum.com/forum/pc-dmis-enterprise-metrology-software/pc-dmis-for-cmms/526356-another-asme-profile-question-ugh
browningdmis
Profile of a surface considers all of the points related to that surface irrespective of whether datums are referenced or not, it is always the same calculation - we look at all of the deviations of all of the points and make them absolute values, then we report 2x the largest value. This is correct as per the ASME Y14.5.1 - 2019 math standard (as explained in the other post). The points from the datum features are not considered when looking for the "max point", what they essentially do is control the amount of best-fitting allowed to decide how the tolerance zone should be located and orientated. With no datums, the tolerance zone is allowed to fully optimize. Adding a primary datum plane (for example) would constrain 2 degrees of rotation and 1 translation, so the tolerance zone would only be allowed to optimize the remaining 1 rotation (about the axis of the primary) and 2 translations. The more datums, the less optimization allowed.
Thanks Neil this is exactly what I needed. It is how I thought it was being done. The powers to be at work say this is a violation of asme 2019. They say once you add in the datum you can not best fit. Your profile becomes bascily a 2d plus minus feature. You profile has to be worst measured point x2 and it does not matter about any other points.
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