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ISO 2692


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Wondering if any ISO guys can help out here. I'm trying to determine how the ISO standard handles Material Modifiers on a Datum (MMB, LMB). We only have access to ASME, just curious how ISO defines MMB. A preview of the standard shows MMS, MMC, MMR, MMVC, MMVS, and similar for LMS, etc...

Also, what is simultaneity in ISO?
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The biggest difference between ISO and ASME when it comes to Datums is how they are constructed.

ASME leans heavily on Outer Tangential where as ISO uses "black-magic".

Here is a quick write-up that I sent to a customer some time ago.

I'd suggest taking the Aukom GD&T course.

"There are also extreme differences regarding the evaluation/construction of Datums. ISO says that for straight lines or plane as a Datum that it is “The datum is the associated adjacent straight line or plane, evaluated by the Chebyshevian principle (or minimum zone principle) and parallel translated into the highest (material side) points or tangential features”. That’s a mouthful, confusing, and as far as I know no measurement software does/can do that. For the axis of a cylinder as a Datum “The datum is the axis of the maximum inscribed cylinder (or minimum circumscribed cylinder in the case of an outer element respectively). In both cases, the datum is the axis of the adjacent feature.” That part is similar to ASME, the only difference lie in that fact that ISO requires you to “probe” parallel to axis of the cylinder which means that you have to measure the axis of the cylinder fist before you can do that – very confusing. ASME requires you to use outer tangential for the Datums."
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