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Thread: Simple Drawing

  1. #21
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    Lines should be tangent to arc at left.
    Dimensions don't match the original drawing.

    Dims and Tangent.jpg
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    Default Dimensional discrepancy?

    Yeah, there seems to be some discrepancy in the original dimensions, as though it was first done in inches, then converted to metric, so that you cannot perfectly hold all of the dimensions, e.g.,
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    All of the dimensions from the original drawing can be honored out to as many decimal places as desired.
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    Quote Originally Posted by JD Mather View Post
    All of the dimensions from the original drawing can be honored out to as many decimal places as desired.
    May be, as the original is quite blurry and a dimension has even been written in by hand for whatever reason.
    When all you have is a hammer, everything looks like a nail.--

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    It seems to me this is another "one of those". The 64mm dim could be very misleading unless the center point is very clearly shown offset. But even then, the 64 is not a necessary dimension. Better to just leave it off.
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    Last edited by neophoible; 20th May 2014 at 07:01 pm. Reason: added "is"
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    The instructor would have been better off selecting pertinent drafting assignments had he/she used French's book "Engineering Drawing" copyright 1947!

    It's pretty amazing the number of these types of assignments that come through with errors and/or omissions in them. Apparently no one checks the diagrams for accuracy, prior to publishing; everyone is keyed in on the text.
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    Quote Originally Posted by neophoible View Post
    The 64mm dim could be very misleading unless the center point is very clearly shown offset. But even then, the 64 is not a necessary dimension. Better to just leave it off.
    You are assuming that the center of the arc is coincident.
    Dimensions on a drawing (unless shown as reference) take precedence over all else.

    In typical classroom type problems these are the tricks that separate the "A" students from the "B" students.
    Instructors look for this attention to detail and throw in tricky stuff like this.

    There is nothing wrong in this part/assignment.

    See Post #7 where I clearly show the dimensions as given in the original drawing.
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    Quote Originally Posted by JD Mather View Post
    You are assuming that the center of the arc is coincident.
    Dimensions on a drawing (unless shown as reference) take precedence over all else.
    Or maybe you are assuming I'm assuming? The 64mm is a dimension, but to what? Maybe I know, if I'm the one originating it. Experience tells me that such a drawing is too easily misinterpreted. The student should be taught to make it clear. It seems to me, this is a case where that is not the case. However, it is a good problem for demonstrating what happens when you don't make it clear. (Hmm. I wonder if anyone can understand that?)
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    Quote Originally Posted by JD Mather View Post
    In typical classroom type problems these are the tricks that separate the "A" students from the "B" students.
    Instructors look for this attention to detail and throw in tricky stuff like this.

    There is nothing wrong in this part/assignment.

    See Post #7 where I clearly show the dimensions as given in the original drawing.
    I think the drawing in post #2 is more appropos to the discussion, and it isn't tricky, it's misleading or incorrect. The 64mm is not an exact dimension when holding all the others exact. Post #7 is where the solution comes in. If the student is told that the center is not along the line, that the 64mm is not exact, then you have a more bona fide problem. Or you could just drop the 64mm dimension altogether.
    When all you have is a hammer, everything looks like a nail.--

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    “Well, if you don’t know, I’m certainly not going to tell you!”

  10. #30
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    Quote Originally Posted by neophoible View Post
    I think the drawing in post #2 is more apropos to the discussion, and it isn't tricky,[I][I] it's misleading or incorrect. The 64mm is not an exact dimension when holding all the others exact. Post #7 is where the solution comes in.
    Post 2 and 7 are the exact same file.
    You are wrong, the drawing is correct. It is an exact dimension holding all others dimensions exactly as given. I am done with this one.

    BTW, it isn't tricky or misleading for the "A" students.
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