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Reporting Basic Dimensions

Discussion in 'Sampling, Standards and Inspection' started by Aaron, Feb 9, 2016.

  1. Aaron

    Aaron Member

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    I'm new to this forum and want to say hello:). Also, hope you ladies and gentlemen will help me out with a question.

    I've been reporting a basic dimension using the tolerance block for the applied tolerance for many years, but I don't believe that I need to report a basic dimension because it's a theoretical value. Normally, a basic dimension is related to a feature that has some sort of GD&T associated with it. Therefore, the basic dimension serves no purpose in a report. Also, my understanding is that no tolerance is applied to basic dimensions.

    My question is has anybody had any issues with their customers by not reporting the basic dimensions on a print? Since there is no value to reporting it, I'm going to save myself some time by not reporting it, but thought someone would have some insight on any repercussions for doing so. Granted, I'll discuss this with my customer prior to stopping it, but would like your feedback.

    Thank you,
    Aaron
     
  2. Emmyd

    Emmyd Member

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    That all depends on your customers. We have one customer that wants to see every dimension (although we do not put judgements on basic dimensions) and another who only wants to see the GD&T & toleranced dimensions on the layout. Some OEM's have a requirement that you have to report everything on the print.

    Hope this helps!
     
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  3. Aaron

    Aaron Member

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    Thank you for the reply; It did help. Ultimately, I'll work with our customers to realize what they expect.
     
  4. James

    James Active Member

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    Do you mean things like the center point of a hole?
     
  5. Aaron

    Aaron Member

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    I mean a basic dimension like the attached picture. This one is from a datum to a hole and the hole has true position associated with it.
     

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  6. ncwalker

    ncwalker Well-Known Member

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    You are correct in that there is no tolerance that can be applied. But as a customer, it pisses me off when you just send me true position results (tolerance) and not the coordinates that generated them (basic). I have no idea if your positional error is all in one direction or a noisy cloud around the center.
     
  7. Aaron

    Aaron Member

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    Thanks, that makes sense. That would annoy me as well. I'll probably just keep reporting it. I would calculate the dimension any ways because it helps me understand the status of the part. The only time it would save me is recording it on the FAI report.
     
  8. Ravi Khare

    Ravi Khare Member

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    Basic Dimension is the true value. Meaning it is the theoretically exact value of the dimension. Basic dimension is only a part of the tolerance definition and not the entire definition.

    For example a position tolerance zone is uniquely defined by Datums, Basic Dimensions and the position tolerance value contained in the feature control frame.

    In isolation none of these three components make sense. Hence, you never measure conformance to a basic dimension in isolation, nor do you aim at achieving basic dimensions on a part in isolation.

    Let me illustrate with a simple example what it would amount to.

    I stay in the third house on a road two blocks north of the city airport. I wish to tell you where I live.

    Reporting a basic dimension would amount to telling you the location of the airport instead of that of my house.

    Reporting just the position would amount to saying live two blocks up north without telling you which airport I am talking about.

    Datum definitions are a must as they tell you where to start the Basic Dimensions from.

    Thus, imho either asking to report anything of the above in isolation or reporting it in isolation conveys no useful information.
     
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  9. Aaron

    Aaron Member

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    Thank you for the explanation and illustration. I liked the illustration.
     

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