3D Surface alignmet

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  • 3D Surface alignmet

    Hi All,
    Need Help here
    I have an aerospace part that is a set of 3D surfaces (free flowing) with no 2D geometric parts on it.
    I have a CAD model & the machined part, how the heck do you measure say 9 points over the surfaces and align these points to the model?

    Sometimes referred to as an RPS alignment in other systems???

    For obvious reasons I cant post any pictures of the model etc…

  • #2
    It sounds like iterative alignment is the way to go. Do you have 3 points on the part that are somewhat planar? Anything to use for rotation?

    Your points do not have to be perfect but the math will need to converge in order to get a solution.

    I get a lot of mold line parts in here that do not have defined local coordinate systems but they are rigged in aircraft absolute coordinates.

    I do not recall a case in which I could not find something on the part that I could use for alignment.

    Hilton Roberts

    "Carpe Cerveza"


    • #3
      Hi Jedit

      Without the drawing I cannot be that specific but I do this type of thing quite a lot when measuring steam turbine aerofoils. You have a few options

      1. Although the surface is free flowing, if surfaces have enough opposing vectors you can do an itterative alignment. This is the preferable choice
      2. Failing the above, normally a combination of 2D or 3D best fit alignments should do the trick.

      Does the drawing specify any datums ?



      • #4
        I have used iterative alignments off of corner radii to get close, the 3d best fits to the surfaces.
        sigpic Life is not a journey to the grave with the intention of arriving safely, but rather a skid in broadside, totally worn, proclaiming WOW What a ride!


        • #5
          The only point I have in the model is on about 4-5 meters away from any surfaces, probably centre of gravity, the best way I can describe the part to give you an idea of how it looks is as follows.

          Make a fist & look at you knuckles, the under side is a combo of varying large spherical surfaces? Talk about give a designer the tools to create something & they will, well this chap certainly as

          BTW I will give your suggestions a go & post the results.


          • #6
            Pick points ON the surface of the cad model, 3 in one common direction, 2 in a different (but common) direction and a single point that does not have the direction in common with the previous points, then measure them and do an iterative alignment. When they said points, they didn't mean c wire frame points, but points ON the model of what you are checking.

            MINIMUM requirements for an iterative alignment:
            6 points, 3 with a common direction, 2 at as close to 90 degrees from the first 3 (with a common direction) than 1 at 90 degree to all the previou points, or 3 points with a vector of 0,0,1, 2 points with a vector of 0,1,0 and one point with a vector of 1,0,0
            Originally posted by AndersI
            I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.


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