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Thread: Noob to gd&t needing guidance

  1. #1
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    Noob to gd&t needing guidance

    First off i would like to say hello to everyone..So hi
    I'm new to gd&t as a inspector and have done some basic jobs which call for gd&t but some things have been holding me up in my progression. Iam based in the uk and work to iso9001 standards and wondered if someone could help me out with the drawing attached?
    As i understand hole position tolerance is measured from the datums stated in the feature control frame. The drawing i have attached is from a customer who use's there own datum reference frame to take measurments from and restrict 12 degrees of freedom,Which i understand.
    The part i'm confused about in the upper drawing arrowed is the positional tolerance that use's hole(Datum) "c" as the tertiary. Do use hole(Datum) B for dimensions left to right of itself and then C for dimensions above and below? So basically if i ran a line through B and a line through C (perp to each other)the point at which the two meet would be my coordinate system?
    Also the same applys to the drawing below it where profile tolerance which calls up datums ABC. Where would my measurments come from? I have measured from the red line highlighted as it is parallel but is this correct?

    Any feedback is greatly appreciated
    Nick
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  2. #2
    Administrator Kelly Bramble's Avatar
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    The dimensioning and tolerancing standard is not ISO 9001 it is probably BS EN ISO-1101 or possibly ASMEY14.5. ISO 9001 is the international standard that specifies requirements for a quality management system (QMS).

    Second,one cannot restrain 12 degrees of freedom since there is only 6 degrees of freedom available.

    As far as the feature control frame or in ISO ~ the Datum Coordinate System or DCS it defines three mutually perpendicular axis and three mutually perpendicular datum planes. Datum A is likely a plane derived from a plane feature on the part, Datum B is an axis accompanied by two datum planes derived from the hole feature. Datum C is technically an axis derived from the hole which is used to orient one of the datum planes derived from datum B.

    Thus,you will have three mutually perpendicular datum axis and planes wherein the origin 0,0,0 is located at Datum B where it intersects Datum A.

    You should seek out ASME GD&T (Geometric Dimensioning and Tolerancing) or ISO G&T (Geometrical Tolerancing) training as applicable.
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  3. #3
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    Thank you for your reply kelly.I''m currently seeking a course or a book that could give good pictorial deatails but really need someone to speak with one to one so i could go through things i stuggle with one drawings. Course's in the uk are really expensive as i would have to fund it myself and i feel a cheaper online course i would not be able to askthe questions i seek the answers to. Could you point me in the direction on some good material please.

  4. #4
    Administrator Kelly Bramble's Avatar
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    Course's in the uk are really expensive as i would have to fund it myself
    It's unfortunate that your employer will not step up and properly train you for the job that you do..for them


    I''m currently seeking a course or a book that could give good pictorial details
    All of my dimensioning and tolerancing books and numerous other GD&T and G&T resources are available on this website. Access to my books requires a premium account. see:

    Geometric Boundaries II, The interpretation and Application of ASME Y14.5-2009

    Geometrical Boundaries, Interpretation and Application of Geometrical Tolerancing per. ISO 1101

    Differences Between ASME Y14.5 and ISO 1101

    Geometric Metrology - Dimensional Tolerances Inspection and Practices in Manufacturing

    And more resources here:

    Dimensioning and Tolerances Books, Resources and White Papers

    Mechanical Tolerances, Engineering Design Fits, Tolerance Calculators and More

    ASME GD&T and ISO G&T Training Videos

    Online Dimensioning and Tolerancing Training Classes:

    GD&T Geometric Dimensioning and Tolerancing Basics Training - ONLINE, Self Paced

    Geometrical Tolerancing, G&T Training, ISO 1101
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  5. #5
    Associate Engineer
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    Thanks Kelly DM sent

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