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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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  • in reply to VinniUSMC
    I understand what you and and are all saying; however, checking the position of a hole pattern to an origin that is 14 feet away seems a bit drastic to say the least! Then we must factor in the accuracy of measuring datum feature B when we only have 19° of a 28 foot diameter!!
    Couple that with the envelope principle of RFS for datum feature C and I'm still wondering the best way with the software to achieve the most accurate and precise measurements while complying with the standard.

    Looking forward to y'alls thoughts!!
  • in reply to VinniUSMC
    Regardless of whether your origin is 14 feet away or not, that is Datum B. The only thing Datum C can do, that isn't already done (can/may/must) is stop rotation about B (or, think of it as rolling the part on the surface that B is pointing at.)

    Search the forum for the instructions for the best practice for measuring a small arc radius.

    Datum C is the midplane of the feature, at whatever size the feature is.

    This is equivalent to any other plane, circle, slot alignment.
  • in reply to VinniUSMC
    14 feet or 14 microns, it says what it says.vinnie is right on this
  • in reply to VinniUSMC
    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.
  • in reply to VinniUSMC
    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.
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