Scales in a Drawing

 

            When you draft on paper, you determine the scale before you start drawing.  This scale is a ratio between the size of the drawn object and the actual size of the object the drawing represents.  For example, each quarter inch in an architectural drawing might equal one foot in the floor plan of a house.  The scale you choose must allow the drawing of the object to fit on the paper selected to represent the object.

            In AutoCAD, this process is reversed.  The object is drawn full size.  Each unit on the screen represents whatever you want it to be: an inch, a millimeter, a kilometer. Therefore, if you are drawing a motor part, one unit might equal a millimeter. If you are drawing a map, one unit might equal one kilometer.  You draw the object with a measurement style you specify: decimal inches, architectural feet and inches, surveying decimal feet, etc.

            You don't need to think about setting a scale until you're ready to print or plot your drawing.  When you print or plot, you then set the scales necessary to position and size the drawing on the page.  Although you do not specify the scale of your drawing until you plot, you should enter, in advance, the scaled size for

            Scaling these elements ensures that they are at the correct size in the final drawing.

 
Specify the Scale Factor in Model Space

 

            If you plan to plot your drawing from the Model tab, you should calculate the exact scale factor by converting the drawing scale to a ratio of 1:n. This ratio compares plotted units to drawing units that represent the actual size of the objects you are drawing.

For example, if you draw at a scale of 1/4 inch = 1 foot, you would calculate the scale factor 48 as follows:

1/4" = 12"  or,  1 = 12 x 4  yielding 1 (plotted unit) = 48 (drawing units)

Example

The sample architectural scale ratios in the table can be used to calculate text sizes in model space.

Scale

Scale factor

To plot text
size at

Set drawing text
size to

1/8" = 1'-0"

96

1/8"

12"

3/16" = 1'-0"

64

1/8"

8"

1/4" = 1'-0"

48

1/8"

6"

3/8" = 1'-0"

32

1/8"

4"

1/2" = 1'-0"

24

1/8"

3"

3/4" = 1'-0"

16

1/8"

2"

1" = 1'-0"

12

1/8"

1.5"

1 1/2" = 1'-0"

8

1/8"

1.0"

If you are working in metric units, you might have a sheet size of 210 x 297 mm (A4 size) and a scale factor of 20. You calculate drawing limits as follows:

210 20 = 4200 mm

297 20 = 5900 mm

 

            Once you establish the scale factor, you can use it to set text height, dimension sizes, linetype scale, hatch pattern scale, and viewport scale. When the drawing is complete, you can plot it at any scale, or you can plot different views of your model at different scales.

 
Apply Scale Factors

 

You set values for the following elements depending on whether you intend to plot from model space or from a layout in paper space.

·   Text. Set the text height as you create text or by setting a fixed text height in the text style (command: STYLE). The text height for text plotted from model space should be multiplied by the scale factor. Text created directly on a layout, in paper space, should be set to true size (1:1).

·   Dimensions. Set the dimension scale in a dimension style (command: DIMSTYLE) or with the DIMSCALE system variable. Dimensions created directly on a layout should be set to true size (1:1).

·   Linetypes. For objects plotted from the Model tab, set the scale for noncontinuous linetypes with the CELTSCALE and LTSCALE system variables. For objects plotted from a layout in paper space, use the PSLTSCALE system variable.

·   Hatch patterns. Set the scale for hatch patterns in the Boundary Hatch and Fill dialog box (command: BHATCH) or with the HPSCALE system variable.

·   Views. When plotting from the layout tab, use ZOOM XP, where XP is the scale (the inverse of the scale factor) of the view relative to the size of the paper.