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Thread: ISO 2768-2 Interpretation

  1. #1
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    ISO 2768-2 Interpretation

    Hello All,
    I need advice on ISO 2768-2. I understand that this is a specification for general tolerances applied to workmanship for non dimensioned features using machining or other material removal means. I have it on a drawing for a part that gets heat treated and there is some distortion after heat treating making the part non compliant.
    My question would the tolerance apply to the part before or after heat treating? The ISO specification mentions nothing about post processing. My contention would be that it applies to the part after machining or metal removal and not after post processing.

    Let me know your thoughts.. and thanks in advance.

  2. #2
    Administrator Kelly Bramble's Avatar
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    Quote Originally Posted by tommci View Post
    Hello All,
    I need advice on ISO 2768-2. I understand that this is a specification for general tolerances applied to workmanship for non dimensioned features using machining or other material removal means. I have it on a drawing for a part that gets heat treated and there is some distortion after heat treating making the part non compliant.
    My question would the tolerance apply to the part before or after heat treating? The ISO specification mentions nothing about post processing. My contention would be that it applies to the part after machining or metal removal and not after post processing.

    Let me know your thoughts.. and thanks in advance.

    The engineering drawing defines the tolerance requirements for the final end item. If the engineering drawing specifies a heat treat, unless otherwise specified the tolerances apply post heat treating or whatever the final deliverable state is.

    Also, ISO 2768 specifies the tolerances of un-toleranced dimensions. In general, ISO 2768 applies to machined/turned parts.
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  3. #3
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    My thought is that in the second paragraph of the scope of ISO 2768-2 that states "applies to features that are produced by removal of material. Its application to features manufactured by other processes is possible; however, special examination is required to ascertain whether the customary workshop accuracy lies within the general geometrical tolerances specified in this part of ISO 2768."
    My thought is that by adding heat treat which is part of the overall process that potential distortion would show that the ISO spec was improperly used or not examined closely enough to lie within the spec boundaries.
    The example part is a round metal stamping and not machined or turned. Again part meets print as stamped but heat treat distortion plays havoc with run out general tolerance in the spec.

  4. #4
    Administrator Kelly Bramble's Avatar
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    The paragraphs referenced do not change the parts dimensional tolerance acceptability post heat treating or any other post process specified on the engineering drawing.

    There should be a note on the engineering drawing such as; "Dimensional and Geometrical Tolerance Limits Apply Before Heat Treating Operations".

    This is actually a common challenge particularly on parts with thin walls or thin wall to thick wall sections as well as parts with significant amounts surface plating.

    When heat treating is going to be a problem it is not uncommon for parts to have before and after heat treating tolerances on critical fit-up features. In some cases, machining allowances of extra material is provided in critical locations with explicit instructions to post machine post heat treating. When thick plating is present design activity may specify the geometry to be nominally small to compensate for the buildup of plating or require masking to prevent the buildup of plating.

    Your counter point is attempting to grey out the standard and engineering drawing specifications. Design, engineering and manufacturing specifications are very much black and white and should be written and interpreted as such.




    Quote Originally Posted by tommci View Post
    My thought is that in the second paragraph of the scope of ISO 2768-2 that states "applies to features that are produced by removal of material. Its application to features manufactured by other processes is possible; however, special examination is required to ascertain whether the customary workshop accuracy lies within the general geometrical tolerances specified in this part of ISO 2768."
    My thought is that by adding heat treat which is part of the overall process that potential distortion would show that the ISO spec was improperly used or not examined closely enough to lie within the spec boundaries.
    The example part is a round metal stamping and not machined or turned. Again part meets print as stamped but heat treat distortion plays havoc with run out general tolerance in the spec.
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

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