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Thread: ISO standard GPS and dimension tolerances and iso 8015 standard

  1. #1
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    ISO standard GPS and dimension tolerances and iso 8015 standard

    Hello to you all, I am new to this forum.

    I try to find experts for the ISO drawing standard, I hope I am in the right place.

    Here are a few questions :

    1. First I would like to know, if I put a dimension, let say a diameter of a cylinder with a tol. of 0/-0.2. does it means that the straightness of cylinder must be 0.2 or lower? or must I state the Geometrical relation along side with the tolerance, what does not make real sense.And In which Std. does this roles stated?

    2. If I understand the Iso 8015 correctly, It means, if stated in the drawing title block, that the dimension's tol. do not apply for the geometric relation (as in the previous question) , hence the "Principle of independency" apply. If so, I could write diameter tol. of 0/-0.2 and straightness of 1. If what I wrote is correct than how do I measure the dimension of the cylinder?

    Please refer to the following drawing:
    As shown on drawing, with the ISO 8015 stated:


    How to measure?, the following drawing shows the measured dimension, is it correct? what "max" dimension will still comply with the upper drawing?



    I hope I have explained my self clearly ,

    Thanks
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  2. #2
    Administrator Kelly Bramble's Avatar
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    Limit tolerances specified to the ISO standard are by default applied by the principle of independency. The principle of independency only requires a simple two point measurement to verify size conformance along the entire length of the feature. To invoke the Envelope Requirement a symbol “Circle E” is clearly associated with the dimension and tolerance or a note.

    Where you applied the straightness tolerance this is an additional requirement for the feature of size.

    The ASME and tANSI standards invoke the Envelope Principle, Rule #1 (Envelope Requirement in ISO) by default for all feature of sizes.
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  3. #3
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    Kelly, thank you for your answer.

    Please see section 7.2 of the Iso 8015:




    It clearly states that in order for the "principle of independency" to apply it must be stated in the drawing. I hope I am not mistaken, all my professional life I thought that the tolerance defines the geometrical tolerance as well .

    I still do not know what "national standards" this principal applies for by default?

    In general, if we consider that the "principle of independency" applies for a drawing, what does a "two-point measurements" means, because the two points that I measure depends on the measuring technique and measuring instruments.

    I am not sure how to make a drawing when this principle applies.
    Is it possible to use this standards only on a specific dimension and not on the whole drawing ?


    Is it possible someone to send me an example of a drawing, Preferably complex drawing and Preferably in the ISO std, that the "principle" is applied there .

    Thank you.
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  4. #4
    Administrator Kelly Bramble's Avatar
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    Yes, an engineering drawing should have the dimensioning and tolerancing standard stated.. in a note or typically in the title block.

    Without a dimensioning and tolerancing standard specified - anything goes.

    By the way, ISO 8015 you linked to is a very old standard, in the UK and most places in the world other than the US the latest dimensioning and tolerancing standard is ISO 1101 - 2017.

    A "two point inspection" is simply done with a dial or digital caliper where the device contacts two opposed surface elements to obtain a distance or size. This measurement is considered 2-dimensional and is allowed by the Principle of Independency though it is considered incomplete as this method does account for the form of the entire feature of size. The feature can be very warped and not revealed by the simple two point measurement. Illustration A & B show a 2-point inspection for a feature of size.


    2-point measurement


    The envelope requirement specifies that all surface elements must be considered or measured in the size measurement. For a hole feature this would be facilitated by sliding the largest gage pin possibile into the as-built hole feature. The gage pin size is then noted and this the actual size relative to the stated MMR (MMC for ASME) size. Additionally a 2-point measurement is done to ensure that the the hole feature is not smaller than the LMR (LMC for ASME) specified. In the illustration below, gage pins are installed until the largest gage pin is determined which does not wiggle or bond while in the as-built hole.



    Measure for the Envelope requirement (ASME Rule #1)
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  5. #5
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    Kelly, thanks again for the answer.

    The ISO 8015 does not replace the ISO 1101 it comes in addition to it. And this is the Standard that states the Principle of independency.

    What I still do not understand is whether Rule #1 applies as default when I state ISO 1101 in the title block or must I add something else?

    furthermore, if I understand you correctly, the two point measurement method is problematic because it does not represent correctly the geometrical form of the part. Sometimes I need a more precise readings and sometimes I can not use a caliper to measure the 2 point dimension. There must be a more accurate definition for the 2 point measure method.

    Thanks ,

  6. #6
    Administrator Kelly Bramble's Avatar
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    If you want to understand ISO 8015 as written in 1983, you need to get the ISO 1101-1983 document as well.

    I would prefer you go find a copy of ISO 1101-2017 or ISO 1101-2011 or even a ISO 1101-2009 and read it and lose that 1983 copy of ISO 8015.

    What I still do not understand is whether Rule #1 applies as default when I state ISO 1101 in the title block or must I add something else?
    Again, when ISO 1101 is stated as the dimensioning and tolerancing standard the Principle of independency applies unless otherwise specified.

    To specify the Envelope requirement for a feature of size, use a Circle E symbol associated with the specific feature of size dimension or a note as applicable. There are other special default applications but I'm not going to introduce them here on the forum..

    ISO 8015-2011


    furthermore, if I understand you correctly, the two point measurement method is problematic because it does not represent correctly the geometrical form of the part.
    No I never wrote that (you got that from somewhere else), it's not problematic unless one needs a 3-D boundary control or a mating part must fit with the feature. There are many features on a part that a 2-point dimension inspection is adequate.

    There must be a more accurate definition for the 2 point measure method.
    I've wrote several times now ... THE ISO ENVELOPE REQUIREMENT!, or ASME Rule #1. It's a 3D tolerance boundary and verification process read up.

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