While on the subject of dimensions, it should be
noted that large objects are seldom drawn to their true
size. Instead, the engineer or draftsman reduces the size
of the object to scale. For example, when drawing a
40-foot tower, the drawing may be prepared using a
scale of 1/2"= 1'-0". In this case, the height of the tower,
on paper, is 20 inches. The scale used to prepare working
drawings is always noted on the drawing. It maybe a
fractional scale, such as discussed here, or a graphic
scale, such as the one shown in figure 3-40. In the Navy,
both numerical and graphic scales are usually shown on
When you are using a drawing, the dimensions of
an object should never be measured (scaled) directly
from the drawing. These measurements are frequently
inaccurate, since a change in atmospheric conditions
causes drawing paper to shrink or expand. To ensure
accuracy, always use the size and location dimensions
shown on the drawing. If a needed dimension is not
shown on the drawing, you should check the graphic
scale, since it will always shrink or expand at the same
rate as the drawing paper.
Drawing notes are used for different purposes and
are either general or specific in nature. One example of
how notes are used are the two notes shown in figure
3-40 that give the inside diameters of the holes. As you
can see, these notes are used for size dimensioning. They
are specific notes in that, by using a leader line, each
note is referred to a specific hole or set of holes.
A general note is used to provide additional infor-
mation that does not apply to any one particular part or
feature of the drawing. For example, the drawing shown
in figure 3-40 could contain a general note saying: All
holes shall be reamed using a tolerance of ± 1/64 inch.
Look at the drawing shown in figure 3-41. This type
of drawing is called a pictorial drawing. These draw-
ings are frequently used to show how an object should
appear after it is manufactured. Pictorial drawings are
used as working drawings for a simple item, such as a
metal washer. For a more complex object, as shown in
figure 3-41, it becomes too difficult to provide a com-
plete description in a pictorial drawing. In this case, it is
common practice to prepare orthographic drawings to
describe the object fully.
Figure 3-41.Pictorial drawing of a steel part.
Figure 3-42.Three-view orthographic drawing of the steel part
shown in figure 3-41.
Assume you are holding the object shown in figure
3-41 in your hands. When you hold the object so you are
looking directly at the top face of the object, the view
you see is the top view. A drawing of that view is called
an orthographic drawing.
Obviously, an orthographic drawing of only the top
view of the object is insufficient to describe the entire
object; therefore, additional orthographic drawings of
one or more of the other faces of the object are necessary.
The number of orthographic views needed to describe
an object fully depends upon the complexity of the
object. For example, a simple metal washer can be fully
described using only one orthographic view; however,
an extremely complex object may require as many as