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Datum Shift

cmm-measurer
ConfusedI received a report from a vendor where they are showing everything on a part 100% in tolerance. I have checked the part myself and show quite a few things out of tolerance. On their report I noticed a term "DATUM SHIFT" and some variables "X,Y,Z", etc. just before each dimension is reported. My question is this, What exactly is "DATUM SHIFT" and what is it doing? Is there some kind of data manipulation going on here?
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  • ConfusedI received a report from a vendor where they are showing everything on a part 100% in tolerance. I have checked the part myself and show quite a few things out of tolerance. On their report I noticed a term "DATUM SHIFT" and some variables "X,Y,Z", etc. just before each dimension is reported. My question is this, What exactly is "DATUM SHIFT" and what is it doing? Is there some kind of data manipulation going on here?


    Datum Shift is a sort of "best fit" that is either trying to mimick a hard gage or account for a material condition modifer on a datum. At least those are the ways it should be used. You are correct in suspecting that it can also be used to made bad parts look good.

    Whether that is the case here or not can not be determined without examining CMM code, (or at least the report) and drawing requirements.
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  • ConfusedI received a report from a vendor where they are showing everything on a part 100% in tolerance. I have checked the part myself and show quite a few things out of tolerance. On their report I noticed a term "DATUM SHIFT" and some variables "X,Y,Z", etc. just before each dimension is reported. My question is this, What exactly is "DATUM SHIFT" and what is it doing? Is there some kind of data manipulation going on here?


    Datum Shift is a sort of "best fit" that is either trying to mimick a hard gage or account for a material condition modifer on a datum. At least those are the ways it should be used. You are correct in suspecting that it can also be used to made bad parts look good.

    Whether that is the case here or not can not be determined without examining CMM code, (or at least the report) and drawing requirements.
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