Iterative alignment help...

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  • Iterative alignment help...

    Im completely green when it comes to iterative alignments. We did run through it briefly during my basic training but since then I have been using Cad=Part.
    I presume that I can use an iterative alignment to measure this helical part (See Att.). I would be forever grateful if somebody could please run through the process with me.

    Thanks in advance,

    Recently jumped from 3.5 Mr 2 CAD
    to 2012 CAD++

  • #2
    What are your datums or are there none on the print?
    Global Status 12-22-10
    Global Performance 9-15-8
    CAD++ 2015.1_SP7


    • #3
      If you don't have your datums called out, this could be a problem, unless you know the application and mounting surfaces. The following is what I would do, if no datums were called out.
      1. Auto Feature - Plane on the flat surface
      2. Auto feature selection - Circle with 3 sample hits on the bottom of your part. the top is not flat.
      3. The offset feature on the top, measure two rads from the underside
      4. Open the iterative alignment widow
      5. Level to the plane
      6. Rotate the two rads
      7. Origin the ctr cir
      8. Then let the cmm remeasure and do an additional dcc alignment per the selected features.

      Hope this may shed a little light on the subject,
      VP A.Gore


      • #4

        As intimidating as iterative alignments may seem, the basic principle of alignment is the same.

        3 - Level points, offset or not, PC-Dmis will attempt to resolve the nominal dimensions you enter, by hand, or by CAD

        2 - Rotation, again, entered points....

        1 - Origin, the third direction.

        All of these will be attempted to be resolved within the fixture tolerance, thereby giving you a 'best fit' condition. If by any range of thought, you can find these 3 items on your part, an iterative alignment will help. I have even had to use the center of 2 - 3D circles along with 1 point on the side to get the level, in essence, cutting a cylinder in half.

        email for more.
        Excercise your mind,..... muscle works better than fat!!


        • #5
          Oi Vey! Thanks Paul et al. I understand now. I was thinking that Iterative alignment was for Jelly/Jello mould type parts (i.e. Parts with no measurable features).
          Just out of interest, how can parts like that be aligned to CAD? Can they? Im using Dmis CAD 3.5 MR BTW.
          Recently jumped from 3.5 Mr 2 CAD
          to 2012 CAD++


          • #6
            Having Bill Cosby issues?? No wonder.

            From what I see, Bottom I.D., top O.D, & one point on that cool step. ALL DIAMETERS NEED 3 SAMPLE HITS.!!!!

            Now, picture the diameters as just center points. VOILA!! Level Y- to the plane of the 3, Rotate Z+ to the center points, use the top O.D. as the origin.

            Note, XYZ are just guesses from the picture, let the demon choose axes from your CAD.

            If you don't get an iterative alignment error, you are there.

            Once it aligns, and you can measure it, toss a little of the engineering pixie dust around to improve any imperfect dimensions. BTW, do you have a crystal ball?

            J/K....couldn't resist, this should work.
            Excercise your mind,..... muscle works better than fat!!


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