ANSWER TO REVIEW QUESTION 1
Concealed features are shown by using the hidden line convention which is a medium line with short evenly
spaced dashes. (para 1-2,b)(fig 1-2)
ANSWER TO REVIEW QUESTION 2
An extension line is a thin unbroken line which is used to extend visible lines. (para 1-2,e) (fig 1-2)
Section II. Projections, Views, and Dimensions
if it were viewed through a transparent drawing plan
1-3.
INTRODUCTION
from an infinite distance (fig 1-6). An orthographic
In learning to read a construction print, you must
projection is made by projecting each point on the
develop the ability to visualize the object, figure 1-5.
object perpendicular to the drawing plane. A
This is done by learning to properly interpret the
pictorial drawing, such as the perspective projection
various types of lines, dimensions, sections, details,
in figure 1-6, presents the object as it would appear to
symbols, and other media that are used to describe
the eye.
the object or parts of an object on a construction
print.
Almost all
a. Orthographic Projection.
drawings intended for production or construction are
drawn by orthographic projection.
(1) The major advantage of an orthographic
projection is that it shows every part of an object that
is parallel to the drawing plane in true relative size
and position.
(2) The numbers of views to be used in
projecting a drawing are governed by the complexity
of the shape of the drawing. Complex objects are
normally drawn showing six views; that is both ends,
front, top, rear, and bottom. Figure 1-7 shows an
object placed in a transparent box. The projections of
the object on the sides of the box are the views seen
by looking straight at the object through each side. If
the outlines are scribed on each surface and the box
opened and laid flat, the result is a six-view,
orthographic projection drawing. It should be noted
that the rear view may appear in any one of four
positions (to the right of the right side view or left of
Figure 1-5. Visualizing from a print.
the left side view, above the top or below the bottom
view).
1-4.
PROJECTIONS
(3) As a general rule, you will find that
An object can be viewed and therefore drawn
most drawings will be presented in three views. For
from an infinite number of positions. Some views
a simple object, three views are adequate to
are easier to draw and interpret than others. It is
completely describe the object when dimensions are
common to present an object on a drawing as an
added (fig 1-8).
orthographic projection or as a pictorial drawing. In
an orthographic projection, the object is presented as
8
Previous Page
