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  1. #1
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    I need help understanding measurements / dimention markings on a datasheet

    Hi all,

    So I am trying to draw a package for a micro SD card holder from Molex however I cannot quite understand some of the markings.
    For example some markings are simple 1.8 meaning 1.8mm however others are for example 2-5.14... or 2-1.0... what does it mean?

    Click image for larger version. 

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    https://static6.arrow.com/aropdfconv...0310831_sd.pdf

    Thank you

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  2. #2
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    Re: I need help understanding measurements / dimention markings on a datasheet

    Consider that the N-xx.x syntax refers to dimensions occurring multiple times. In case of 2-5.14 this is a bit confusing because 5.14 is also printed separately for the upper pin.


    You could also consider that the picture is the copy of a correctly dimensioned CAD drawing. So you can always scale it accordingly and check the dimensions with a ruler, or even convert it to dxf and use it to check your footprint pin placement.



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  3. #3
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    Re: I need help understanding measurements / dimention markings on a datasheet

    i don't think that drawing is correctly dimensioned

    the current practice is to measure everything from one reference, usually the lower left
    so that tolerances do not build up

    the values in the drawing are likely correct, as Molex is reliable, but the drawing does not follow best practices

    as for the drawing being a copy, it looks like a small piece of the drawing in the link
    there is no reason to believe photocopies and PDFs maintain dimension
    if you measure the drawing, start by checking several short dimensions and several long dimension in both directions



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  4. #4
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    Re: I need help understanding measurements / dimention markings on a datasheet

    the current practice is to measure everything from one reference, usually the lower left
    Should be so, but incremental dimensions seem to be popular, particularly in Japanese and Chinese data sheets. No reason to assume that the dimensions are wrong.

    - - - Updated - - -

    You can download a STEP 3D-file from Molex and export it to *.dxf
    Should give you exact dimensions.

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  5. #5
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    Re: I need help understanding measurements / dimention markings on a datasheet

    Ureka moment! 8-1.1 means qty 8, size 1.1mm



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  6. #6
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    Re: I need help understanding measurements / dimention markings on a datasheet

    Better still read the DXF into your cad package and use as a base for the component.



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