An Alternative to Limits

An Alternative to Limits
As an alternative to setting up the drawing limits, you can draw a rectangle that outlines the same
area used to define the drawing limits. For example, in the previous exercise, you could use the Rectangle
tool to draw a rectangle that has its lower-left corner at coordinate 0,0 and its upper-right corner
at 132,102 (297,210 for metric users). You can set up the rectangle to be visible without printing using
the Layer feature. You’ll learn more about layers in Chapter 5.



Understanding Scale Factors
When you draft manually, you work on the final drawing directly with pen and ink or pencil. With
a CAD program, you’re a few steps removed from the finished product. Because of this, you need a
deeper understanding of your drawing scale and how it’s derived. In particular, you need to understand
scale factors. For example, one of the more common uses of scale factors is translating the size of
a graphic symbol, such as a section symbol in an architectural drawing, to the final plotted text size.
When you draw manually, you draw your symbol at the size you want. In a CAD drawing, you need
to translate the desired final symbol size to the drawing scale.
When you start adding graphic symbols to your drawing (see Chapter 4), you have to specify a
symbol height. The scale factor helps you determine the appropriate symbol height for a particular
drawing scale. For example, you may want your symbol to appear 1⁄2˝ high in your final plot. But
if you draw your symbol to 1⁄2˝ in your drawing, it appears as a dot when plotted. The symbol has
to be scaled up to a size that, when scaled back down at plot time, appears 1⁄2˝ high. So, for a 1⁄4˝ scale
drawing, you multiply the 1⁄2˝ text height by a scale factor of 48 to get 24˝. Your symbol should be
24˝ high in the CAD drawing in order to appear 1⁄2˝ high in the final plot. Where did the number 48
come from?
The scale factor for fractional inch scales is derived by multiplying the denominator of the scale
by 12 and then dividing by the numerator. For example, the scale factor for 1⁄4˝ = 1´-0˝ is (4 × 12)/1, or
48/1. For 3/16˝ = 1´ -0˝ scale, the operation is (16 × 12)/3, or 64. For whole-foot scales such as 1˝ = 10´,
multiply the feet side of the equation by 12. Metric scales require simple decimal conversions.
You can also use scale factors to determine your drawing limits. For example, if you have a sheet
size of 11˝ × 17˝, and you want to know the equivalent full-scale size for a 1/4˝-scale drawing, you
multiply the sheet measurements by 48. In this way, 11˝ becomes 528˝ (48˝ × 11˝), and 17˝ becomes
816˝ (48˝ × 17˝). Your work area must be 528˝ × 816˝ if you intend to have a final output of 11˝ × 17˝
at 1/4˝ = 1´. You can divide these inch measurements by 12˝ to get 44´ × 68´.
Table 3.2 shows scale factors as they relate to standard drawing scales. These scale factors are the
values by which you multiply the desired final printout size to get the equivalent full-scale size. If
you’re using the metric system, you can use the drawing scale directly as the scale factor. For example,
a drawing scale of 1:10 has a scale factor of 10; a drawing scale of 1:50 has a scale factor of 50;
and so on. Metric users need to take special care regarding the base unit. The examples in this book



If you’re working on a drawing from an older version of AutoCAD, you’ll use scale factors to
specify text height and dimension settings, so understanding them now will pay off later. Plotting
to a particular scale is also easier with an understanding of scale factors.