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Iterative alignment and using XactMeasure

BWIZZLE
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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  • Thank you for the thorough explanation of Iterative alignments. I think there is one misunderstanding, that is entirely my fault, because I did not explain it entirely.Slight smile My customer supplied model comes to me with the CAD origin (Trihedron) in aircraft/car body coordinates. I then transform my model in a way that it is square with my machine and the origin is now in a hole that we do a read point alignment with and run the entire part in DCC. So my question is if my trihedron is not at the A-B-C alignment, how do I report my true position, and profile dimensions to a A-B-C FCF? I do not want my report in aircraft or car body coordinates either. I want my dimensions to come from my Datums A-B-C. I think this eliminates using a Iterative alignment, because I did some tests today and the Iterative alignment will use the origin from wherever it is on the model, not necessarily from the Datums?

    If you transform the origin to be where the origin of ABC is, then when you run the iterative alignment, it will be in the ABC datum reference frame.

    [hijack]
    Josh, I appreciate the detailed explanations here. Like BWIZZLE, I went to Level 2 training but never fully grasped Iterative alignments because our shop does not make use of them. I have to ask, though, if the origin does not move following iteration then what is the value of this type of alignment?

    I only use alignments to manipulate the coordinate system as a means for measuring other features. If Iterative Alignment instead moves the measured values closer to the nominals then is the goal only to reduce probing error of the alignment features? Would I then create a regular alignment to move my coordinate system to the alignment features?

    I've tried many times to wrap my head around this, but I just can't seem to understand the application.
    [/hijack]

    The origin doesn't move because you are moving the measured data as close to nominal as possible. It is similar to putting a part on a fixture. The fixture doesn't move, the part fits to the fixture. In this same line of thought, you are moving the part (measured data) onto the fixture (nominal data). This is most useful when you are required to report part coordinates in car body alignment, rather than to the DRF. Or, more technically, the DRF is car body, and the cad nominals give your basic offsets and rotations, such that the part is positioned to the car body DRF.
Reply
  • Thank you for the thorough explanation of Iterative alignments. I think there is one misunderstanding, that is entirely my fault, because I did not explain it entirely.Slight smile My customer supplied model comes to me with the CAD origin (Trihedron) in aircraft/car body coordinates. I then transform my model in a way that it is square with my machine and the origin is now in a hole that we do a read point alignment with and run the entire part in DCC. So my question is if my trihedron is not at the A-B-C alignment, how do I report my true position, and profile dimensions to a A-B-C FCF? I do not want my report in aircraft or car body coordinates either. I want my dimensions to come from my Datums A-B-C. I think this eliminates using a Iterative alignment, because I did some tests today and the Iterative alignment will use the origin from wherever it is on the model, not necessarily from the Datums?

    If you transform the origin to be where the origin of ABC is, then when you run the iterative alignment, it will be in the ABC datum reference frame.

    [hijack]
    Josh, I appreciate the detailed explanations here. Like BWIZZLE, I went to Level 2 training but never fully grasped Iterative alignments because our shop does not make use of them. I have to ask, though, if the origin does not move following iteration then what is the value of this type of alignment?

    I only use alignments to manipulate the coordinate system as a means for measuring other features. If Iterative Alignment instead moves the measured values closer to the nominals then is the goal only to reduce probing error of the alignment features? Would I then create a regular alignment to move my coordinate system to the alignment features?

    I've tried many times to wrap my head around this, but I just can't seem to understand the application.
    [/hijack]

    The origin doesn't move because you are moving the measured data as close to nominal as possible. It is similar to putting a part on a fixture. The fixture doesn't move, the part fits to the fixture. In this same line of thought, you are moving the part (measured data) onto the fixture (nominal data). This is most useful when you are required to report part coordinates in car body alignment, rather than to the DRF. Or, more technically, the DRF is car body, and the cad nominals give your basic offsets and rotations, such that the part is positioned to the car body DRF.
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