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Readpoint in front of an iterative alignments?

METROLOGY_GUY76
Hello fellow Metrologist!
My question is going to be geared more to the Gurus here on PC DMIS forum; I have an aerospace part that has target points A1,A2,A3,B1,B2,C1 ....I know how to create an iterative alignment...however, what I usually do is make a readpoint in a location where I can do a small alignment, changing the location of the trighedron...However, the customer has supplied the CAD and wishes for us to keep the location were it is....its in a place you could not create a readpoint without going through the part.
How do i create a readpoint that goes directly into the iterative?
Thanks in advance.
  • Hi, If you select a feature from the CAD, I.e. a hole and note down the XYZ. Create your readpoint and origin it, then create an alignment and offset (normally negative) your XYZ so that your origin is back in the CAD alignment, then in theory you should then be able to start your alignment feature measurement. Note that it's only the XYZ affected with no rotation or level so would only really work with a 'flat, square' part.
  • Hi, If you select a feature from the CAD, I.e. a hole and note down the XYZ. Create your readpoint and origin it, then create an alignment and offset (normally negative) your XYZ so that your origin is back in the CAD alignment, then in theory you should then be able to start your alignment feature measurement. Note that it's only the XYZ affected with no rotation or level so would only really work with a 'flat, square' part.

    I can confirm that this method works. It can also work if you need to rotate the alignments - if the origin of the part is not in the same orientation as the part as it sits on the CMM.

    When doing this, I find it helpful to import a model of a cube into the model assembly and translate the corner of that cube to the origin of the part model. Also translate the rotations of the cube to match the part model. Then, there is reference point that can be selected to ensure that all of the alignments worked out properly in the end.

    Be sure to use nice big prehit and retract values on the iterative alignment hits to help find the part. All of this assumes that you have a good fixturing method that orients the part in a reliable manner.​
  • Import the CAD to an orientation that makes sense to you..

    Do your readpoint alignment as desired..

    Find the part datums as instructed on the print. Create your datum alignment..

    Create a new alignment (recalling your datum alignment) and offset per customer requirements so it matches the nominal values they want Sunglasses
  • Import the CAD to an orientation that makes sense to you..

    Do your readpoint alignment as desired..

    Find the part datums as instructed on the print. Create your datum alignment..

    Create a new alignment (recalling your datum alignment) and offset per customer requirements so it matches the nominal values they want Sunglasses

    That's how I would do it.
  • We have started using 2 Readpoints in holes or on pins and 1 vector point in manual or DCC to establish the first Iterative datum, then use DCC Iterative to establish the print ABC as required.
    HTH!
  • in reply to DAN_M
    Problem with that is the target points are underneath the part, however, the way the customer wants us to pick up the points is how they have it orientated...meaning they prefer we do not translate their CAD coordinate system but rather use as is....so that creates a problem when trying to create the initial readpoint. So, I have decided, now that I have to initially( temporarily) orientate the CAD system on top of the part so that I can use the readpoint and small manual alignment, then rough dcc alignment, going into the iterative alignment...let me know what you think about that?
    Also, I appreciate your help..
    Regards..
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