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Thread: Finishing dimensions

  1. #1
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    Question Finishing dimensions

    Is it a drawing requirement that there must be a statement that dimensions apply after finish?
    Paint, plating etc.If it is not called out on the drawing do all dimensions apply before finish?
    Is there a standard that will reference this?

  2. #2
    Administrator Kelly Bramble's Avatar
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    If your engineering drawing is specified to any of the American dimensioning and tolerancing standards or ISO then there should be a note or other specification that clearly indicates whether the dimensional limits apply before or after application plating, finishing, coatings or whatever...

    Such note is not required if the finishing process does NOT effect the dimensional size, such as a conversion coating.

  3. #3
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    Or -- Add a call-out defining the finishing to the bare materials and specify important issues such as thickness, hardness, corner thinning etc.

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    My problem is I have customer supplied drawings for machined aluminum 6061 with a close tolerance of +/-.004 and surface finish of primer and epoxy paint.
    The parts are close to top tolerance condition before paint.If the epoxy build up is more than .001 they will be out.The drawings do not state whether the dimensional limits apply before or after application of finish. Is there a standard that says if not noted the drawing all dimensions apply before finishing?

  5. #5
    Administrator Kelly Bramble's Avatar
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    Quote Originally Posted by Ant View Post
    Is there a standard that says if not noted the drawing all dimensions apply before finishing?
    No, there is not...

    ASME Y14.5 - 2009, the latest and greatest dimensioning and tolerancing standard explicitly says;

    plating.gif

    Your customer needs to clarify the engineering drawing as to when the dimensional limits apply.

  6. #6
    Technical Fellow jboggs's Avatar
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    Ant - in your case, the standard is whatever your customer says it is. If he is unhappy with the parts you supply, it will not matter to him what some guys on an engineering forum said. It also will not matter to him what some standard says. He is the customer, and that makes him right. Do not hesitate to ask him what his intent is. He will appreciate your consciientious attitude. Point out the details of what you have found in your analysis of the dimensions and the finish requirements and just ask him to clarify, preferably in writing, what his standard of judgment will be. If he thinks you should have already known the answer simply point out that other customers have applied different standards and you just want to make sure he is happy with your work.

  7. #7
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    Quote Originally Posted by Ant View Post
    My problem is I have customer supplied drawings
    {sigh} Had you stated that at the beginning, you would have received an answer along the lines of JB's last post and saved some frustration and you some time.

    As JB alludes, ask the customer what he/she wants. It is totally irrelevant whether there is a Code or not and what that Code might be.

    Try this, "ring - ring - ring - hey, are these dimension before or after the two paint layers?"
    Followed by, "thanks, can you please send a revised drawing with that information."

    Problem solved.

  8. #8
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    Yup this is the way to save your parts/job/business now a day. Evenly, most of drawings I've worked on, if not noted then they are for "AFTER" but hey some customers they want "their" ways so just ask when you doubt!
    But don't forget "DO IT IN WRITING".

  9. #9
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    OK, it appears the previous responses provided to ANT concerning this question are based on the assumption the customer is “Human”.
    What if the customer is the US Government? (Need I say more!) And on top of that, the items you are manufacturing are “Legacy KC-135 aircraft parts” designed in the 1960’s?

    What were the aircraft industry design standards back then? More specifically, what was BOEING’s standard concerning this issue?

    I have access to hundreds of BOEING specifications and standards. I even have a 1955 BOEING Training Manual on Blueprint Reading! While they discuss the application of finish codes, they never address this issue. So any hard reference/indication to the state at which dimensional tolerances applied by this OEM continues to eludes me.

    I have multiple examples of instances where drawings for the same aircraft have statements like “omit primer from this hole” or “Omit primer from this surface” or “THIS dimension applies after plating”. All of which point to a standard (for this aircraft at least) being “All dimensions apply before processing, except as noted”. Which makes sense?

    Is there anyone out there familiar with the aircraft industry that can provide or reference specifications/documentation from that era indicating standard BOEING Company design practices concerning this issue?

  10. #10
    Technical Fellow jboggs's Avatar
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    Don,
    In my mind the same principle applies. You have done your research and have found no clear cut widely known and accepted standard to apply to your question. Whether your customer wears a US Govt hat or a no hat at all, someone somewhere will decide to either accept or reject your product. Someone placed the original order and will decide to pay you or not. That is the person you should be asking. Or send a (dated) notice to your customer contact of your research into the question and your intent to interpret drawing information in a certain way, giving them time to respond if they choose to.

  11. #11
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    Yes it is. The dimemsion should always be indicated in the drawings. Otherwise, you will not know how to measure it

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