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Thread: Scale conversion engineering drawings

  1. #1
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    Scale conversion engineering drawings

    I'm trying to understand scales on engineering drawings.

    I have a plan view drawing of a proposed electrical room on an 11''x17'' size sheet of paper. If the scale is marked 1/2"=1', is this the scale for the full-size drawing? What size paper is used for full-size drawings? How is the scale adjusted for 11"x17" paper?

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    Quote Originally Posted by t_van View Post
    I'm trying to understand scales on engineering drawings.

    I have a plan view drawing of a proposed electrical room on an 11''x17'' size sheet of paper. If the scale is marked 1/2"=1', is this the scale for the full-size drawing? What size paper is used for full-size drawings? How is the scale adjusted for 11"x17" paper?
    If they have marked as scale 1/2 inch equals one foot, then every half inch marked on the paper is supposed to equal 1 foot, or the paper itself covers an area of 22 foot by 34 feet...

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    Quote Originally Posted by t_van View Post
    I'm trying to understand scales on engineering drawings.

    I have a plan view drawing of a proposed electrical room on an 11''x17'' size sheet of paper. If the scale is marked 1/2"=1', is this the scale for the full-size drawing? What size paper is used for full-size drawings? How is the scale adjusted for 11"x17" paper?
    hard to say
    the way I do it is find a labelled dimension on the civil or architectual dwg and scale it
    some tmes they put a bar graphic scale on the dwg that is say 1" = 8'
    if you measure it at 1/2' you are 1" = 16'

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    Sorry, but that is not enough information. I would say that the scale is associated with the "full size" drawing. But there are several possibilities for what "full size" means. If that information is not shown on the drawing, you would have to ask the engineer. As an example, if the full size is 22 x 34, your 11 x 17 is a half size sheet. The scale as shown on that piece of paper is therefore 1/4" = 1'.

    In an ideal world, the engineer would have included a "graphic scale." That is a line with marks along it, and with numbers beside the marks declaring that "this mark is at a distance of 4 feet from the origin" and "this mark is at a distance of 10 feet from the origin" etc. That scale would appear at the same scale (e.g., your 1/2" = 1') when the drawing is plotted at full size. Thus, when the drawing is shrunk so as to fit on a smaller sheet of paper, the graphic scale shrinks along with the floor plan. You can use the distances shown on the graphic scale to directly measure distances on the drawing.
    Charles E. Beck, P.E., Seattle
    Comments based on 2017 NEC unless otherwise noted.

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    Quote Originally Posted by t_van View Post
    I'm trying to understand scales on engineering drawings.

    I have a plan view drawing of a proposed electrical room on an 11''x17'' size sheet of paper. If the scale is marked 1/2"=1', is this the scale for the full-size drawing? What size paper is used for full-size drawings? How is the scale adjusted for 11"x17" paper?
    If "full size" means 22" X 34", then 1/4" = 1' at 11" X 17". If it doesn't say what full size means, then you'll have to find something on the drawing that you at least sort of know its dimensions and measure it.

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    Quote Originally Posted by ggunn View Post
    If "full size" means 22" X 34", then 1/4" = 1' at 11" X 17". If it doesn't say what full size means, then you'll have to find something on the drawing that you at least sort of know its dimensions and measure it.
    This is the best way to go.

    It is also possible that 11x17 is full size, depending of what you are looking at.

    Try to find a door or something that generally you can guess at the size and measure that and reverse figure out the scale.
    Ron

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    Back when I learned drafting (no CAD), the original had a letter associated with the size and was plainly indicated in the title block. ‘A’ size = 8-1/2 x 11, ‘B’ = 11 x 17, ‘C’ = 22 x 34, etc.

    So one could always tell the original size regardless of what the printed size was.

    The company I worked for all my career followed this convention.

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    If you look at it from a Draftsman's perspective, we all use ANSI Standards. Here is information from an ANSI request, "An engineer's scale is a tool for measuring distances and transferring measurements at a fixed ratio of length. ... Referred to as 1:10, 1:20, 1:30,1:40, 1:50 or 1:60 scale. Typically in civil engineering applications, 1:10 (1″=10′)is used exclusively for detail drawings. 1:20 and 1:40 scales are used for working plans".

    From a Design Engineer's standpoint, the Model or what you are drawing is never Scaled to fit paper. You make your Drawings or Models to size (i.e 1:1 or 1"=1") and scale at the Printer or Plotter to fit the 1:1 Drawing to the paper. Modern Drafting and Modeling Software most often has the Scale displayed automatically when Printing / Plotting. ANSI gives Standards for Drawing sizes as in A (8 1/2"x11") B (11"x17") C (18"x24) D (24"x36") on up. The preference is to print at 1:1 so that a person making something from your drawing can place the part on the drawing and everything lines up. That's a little hard to do for Architects so pretty much everything is Scaled to fit the Paper it is Plotted on.

    A problem crops up when a PDF of a C size drawing is printed on a regular Printer at 8 1/2" x 11". If the scale that is from the original Drawing is displayed for "C" Paper but printed on A paper, the Scale will be wrong. It will still be proportional so as others have said, find something that is standard and you can calculate a Multiplier or a Divider if you are going to measure the drawing then use the measurement to make or construct something. If the measurement were correctly included for the "C" size Paper, they will be accurate regardless what the paper size is. By that I mean that if the drawing shows a placement of 4ft to the left of a doorway and 5 ft up from the floor; that won't change regardless of what paper size is used for the Drawing.
    Hope that helps,
    JimO

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    Quote Originally Posted by jimo144 View Post
    Typically in civil engineering applications, 1:10 (1″=10′) is used exclusively for detail drawings.
    1" = 10' is 1:120 scale, isn't it?

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