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Construct Plane: using 2 surfaces what is the best approach?

BIGWIG7
I have a datum that is 2 separate plane surfaces with opposing vectors but on the same center line.

What is the best approach: creating a few independent points on both surfaces and combining them into one plane OR creating 2 separate planes and then Constructing a plane from them?

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  • I have a datum that is 2 separate plane surfaces with opposing vectors but on the same center line.

    What is the best approach: creating a few independent points on both surfaces and combining them into one plane OR creating 2 separate planes and then Constructing a plane from them?



    It is hard to say what is the best approach. I think it would depend a lot on the situation.

    If you have callouts that use MMB on that datum, then I'd certainly suggest you use a width feature to take advantage of the bonus tolerance. Same goes for if there is MMC or LMC on the datum callout itself.

    If you are using the newer GeoTol reporting. I think you would technically want to use a width feature because it will then be treated as a datum simulator. Under ASME It would use a constrained least squares fit on the points to sit on the high spots, as if you were using a functional gage. Under ISO, it would do the same thing, but filters out outliers first.

    Check out the Width section of this page of the help file. There is lots of good info there: How PC-DMIS Solves and Uses Datums (hexagonmi.com). ​
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  • I have a datum that is 2 separate plane surfaces with opposing vectors but on the same center line.

    What is the best approach: creating a few independent points on both surfaces and combining them into one plane OR creating 2 separate planes and then Constructing a plane from them?



    It is hard to say what is the best approach. I think it would depend a lot on the situation.

    If you have callouts that use MMB on that datum, then I'd certainly suggest you use a width feature to take advantage of the bonus tolerance. Same goes for if there is MMC or LMC on the datum callout itself.

    If you are using the newer GeoTol reporting. I think you would technically want to use a width feature because it will then be treated as a datum simulator. Under ASME It would use a constrained least squares fit on the points to sit on the high spots, as if you were using a functional gage. Under ISO, it would do the same thing, but filters out outliers first.

    Check out the Width section of this page of the help file. There is lots of good info there: How PC-DMIS Solves and Uses Datums (hexagonmi.com). ​
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