Engineering Fundamentals: An Introduction to Engineering, 4th ed.c

Now if you were to draw perpendicular lines from the corners of the object into the faces of the

glass box, you would see the outlines shown in Figure 16.1. The outlines are called the ortho-

graphic projection of the object into thehorizontal,vertical, and theprofile planes.

Now imagine that you open up or unfold the faces of the glass box that have the projections

of the object. The unfolding of the glass faces will result in the layout shown in Figure 16.2.

Note the relative locations of the top view, the bottom view, the front view, the back view, the

right-side view, and the left-side view.

At this point, you may realize that the top view is similar to the bottom view, the front view

is similar to the back view, and the right-side view is similar to the left-side view. Therefore, you

notice some redundancy in the information provided by these six views (diagrams). Therefore,

you conclude that you do not need to draw all six views to describe this object.

In fact, the number of views needed to describe an object depends on how complex the shape

of an object is. So the question is, then, how many views are needed to completely describe

the object. For the object shown in Figure 16.1, three views are sufficient to fully describe the

object, because only three principle planes of projection are needed to show the object. For

the example shown in Figure 16.1, we may decide to use the top, the front, and the right-side

views to describe the object completely. In fact, the top, the front, and the right-side views

are the most commonly created views to describe most objects. These views are shown in

Figure 16.3.

From examining Figure 16.3, we should also note that three different types of lines are used

in the orthographic views to describe the object:solid lines,hiddenordashed lines,andcenter-

lines. The solid lines on the orthographic views represent the visible edges of planes or the inter-

section of two planes. The dashed lines (hidden lines), on the other hand, represent an edge of a

plane or the extreme limits of a cylindrical hole inside the object, or the intersection of two planes

that are not visible from the direction you are looking. In other words, dashed lines are used

when some material exists between the observer (from where he /she is looking) and the actual

location of theedge. Referring to Figure 16.3, when you view the object from the right side, its

16.2 Orthographic Views 509

To p

Bottom

Back Left Front Right

■Figure 16.2 The relative locations of the top, bottom, front, back, right-side, and left-side views.

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