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Plane, Circle, Width Alignment ???

RIDER
I have gained so much over the years from the contributors of this forum. Thank y'all for sharing your wisdom, knowledge, and experiences!

With that said, I would like your opinions on the attached crude drawing. It's third angle projection and in accordance with ASME Y14.5M-1994. The material at it's thickest point is 1 1/4". The total length of the part is 60". Here are the questionsRelaxed

1. How would you align this part for the position and profile call-outs back to ABC?
2. Since B is a huge diameter and C is a width, what would you use to rotate to?
3. PC-DMIS can't solve a constructed line from a circle/cylinder (B) to a width/mid-line/mid-plane (C). So what would you use instead to comply with the standard and satisfy the software?

There's some dissension here with regard to designer intent as well as compliance to the standard.

Thank y'all again for taking the time to share!!!
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  • I've been using the small arc method for years and understand all of the principles/techniques for creating sound alignments that lock down all 6 DOF. I guess my major question is about design intent? If you were to make a check fixture for this part, how would the position of the holes relate to a center point 14 feet away? Yes, datum C is stopping the rotation by fitting into a slot. So to create this line from B to C, what would you use? (opposing points to create primary (tangent) planes and then construct a mid-plane, just 2 opposing points to create a mid-point, a mid-line that pierces datum B, etc.)

    I was hoping to gain some opinions on accurate, repeatable, compliant measurements for the stated datum scheme and associated call-outs.

    A 28 foot diameter Datum B virtual condition pin... Slight smile

    Yeah, making a check fixture would require some engineering, and obviously would have to be clever about that 28 foot stab. I would want to use some sort of spring loaded pins or fingers that can fit to the diameter as it changes. But, on the CMM, your software doesn't care how big the diameter is.

    I would use the center point of B, and construct a mid-point from opposed points on the center of C (assuming the sides are parallel to the B-C line nominally).

    Do you have CAD? If you do, let the software do the work. The only part of this that's not as straight forward is the 20 degrees of arc, but that's controllable.

    Explain to me why you are using B-C to rotate to when C can rotate by it's self. My thinking is that since B can't rotate by it's self but C can, you should use C. Now if C was also a circle and couldn't rotate to either B or C alone, then I would use B-C to rotate.

    I know the above sounds rude and dictating but I don't mean it that way. I am genuinely wanting to know if my thinking is wrong and I'm explaining what my logic is. Read it for what it is with no attitude or emotion attached. One thing I hate about typing is that you can't convey attitude or emotion.

    Can-may-must. If it can, and it may, then it must. If B is the origin in X and Y, then the only thing left is rotation about Z. If you rotate to the slot, then B is no longer your origin. Yes, C can, but because B already does, then it may not (mayn't? lol). Therefore it mustn't.
  • in reply to VinniUSMC
    For a case like this, why is the rotation set by -C- dependent on the origin set by -B-? Why couldn't you just rotate to datum -C- and origin on datum -B-?
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