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Iterative alignment and using XactMeasure

Alright here is my problem/question.
I have a part where Datum -A- (Z axis) is not prismatic, however datum -B- (X axis) and -C- (Y axis) are.

I do not have much experience with Iterative alignments other than that I have been to the Level 2 Hexagon class (Just don't use them or have the need too).

My thoughts were, this is a good time, to try an Iterative alignment.
I believe I have that part of the program correct:
I created 6 auto vector points on top (Datum -A-),
then 5 auto vector points on left side (Datum -B-)
then finally 5 auto vector points on the front of the part (Datum -C-).

When I create the Iterative alignment I pick top 6 points as level (Datum -A-),
5 points on left rotate (Datum -B-),
then 5 points on front as origin (Datum -C-).

After completing this Iterative alignment my trihedron doesn't move from before the alignment.
So I constructed planes out of the five points for datum -B- and -C- respectively.
I then origin my "X" to Datum -B- and my "Y" to datum -C-.
How do I origin my "Z", and how do I assign my datum -A- for exact measure? Where did I go wrong? Please any help would be greatly appreciated.
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  • Yep, now read what you didn't highlight....

    "A mathematically defined feature shall be defined within a three-dimensional coordinate system. Where such a feature (datum target) is specified as a datum feature, it's datum feature simulator (derived from the math data) is used in establishing the datum reference frame."

    Don't grab the first bit and the last bit and ignore what's in between.



    Quite - you can't just decide for yourself which points to use.

    Think about it this way, if the surface was convex in nature it wouldn't have three 'high' points, in order to establish a 'plane' which is used as the primary axis of your DRF (and which obviously has to have some fixed relationship to the other features of the part) you'd need to know which points to use. To continue the analogy imagine you were loading this part (upside down) onto a holding fixture (three supports for the curved surface, two stops for Datum B and one stop for Datum C, depending where you placed the three supports for datum A the part could have a myriad of possible orientations - this is no basis for a part inspection.
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  • Yep, now read what you didn't highlight....

    "A mathematically defined feature shall be defined within a three-dimensional coordinate system. Where such a feature (datum target) is specified as a datum feature, it's datum feature simulator (derived from the math data) is used in establishing the datum reference frame."

    Don't grab the first bit and the last bit and ignore what's in between.



    Quite - you can't just decide for yourself which points to use.

    Think about it this way, if the surface was convex in nature it wouldn't have three 'high' points, in order to establish a 'plane' which is used as the primary axis of your DRF (and which obviously has to have some fixed relationship to the other features of the part) you'd need to know which points to use. To continue the analogy imagine you were loading this part (upside down) onto a holding fixture (three supports for the curved surface, two stops for Datum B and one stop for Datum C, depending where you placed the three supports for datum A the part could have a myriad of possible orientations - this is no basis for a part inspection.
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