Technology: Engineering Our World, 7th Edition Page 75 (75 of 560)

Chapter 3 Communicating Design Ideas
75
gure 3-18. Add details such as doors and
windows.
gure 3-19. Remove construction lines to
complete the house.
Draw a horizontal base line.
Draw an axis (line 1) at right angle (90°) to
base line.
Draw a pair of axes (lines) 30° up from the
horizontal. (You can judge this by dividing
right angles into three equal parts).
Erase extra lines. Extend lines 2 and 3.
Draw other lines parallel to the three axes
to complete the box.
Baseline
1
1
2
3
3
1
2
30°
30°
30°
30°
1.
2.
3.
4.
5.
gure 3-20. You can make a freehand isometric sketch by following these steps.

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Chapter 3 Communicating Design Ideas
75
gure 3-18. Add details such as doors and
windows.
gure 3-19. Remove construction lines to
complete the house.
Draw a horizontal base line.
Draw an axis (line 1) at right angle (90°) to
base line.
Draw a pair of axes (lines) 30° up from the
horizontal. (You can judge this by dividing
right angles into three equal parts).
Erase extra lines. Extend lines 2 and 3.
Draw other lines parallel to the three axes
to complete the box.
Baseline
1
1
2
3
3
1
2
30°
30°
30°
30°
1.
2.
3.
4.
5.
gure 3-20. You can make a freehand isometric sketch by following these steps.

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76
Technology: Engineering Our World
Perspective sketching provides the most realistic picture of objects. g
The sketches are drawn to show objects as we would actually see them.
Parallel lines converge and vertical lines become shorter as they disappear
into the distance. Refer to Figure 3-22 as you read the following steps for
drawing a perspective sketch of a block:
1. Draw a faint horizontal line to represent the horizon. Mark two
points, one at each end of the line. These are vanishing points (VP).
2. Draw the front vertical edge of the block.
3. Draw faint lines from each end of the vertical edge to the vanishing
points.
4. Draw vertical lines to represent the left and right edges of the block.
The length of these vertical sides will be shorter than the real object.
5. Join the top of these vertical lines to the vanishing points. Darken
the outline of the object.
Orthographic Projection
You have learned that isometric and perspective sketches are quick
methods of recording your ideas and communicating them to other
people. They give a general idea of the shape and features of an object.
Unfortunately, there are some disadvantages to isometric and perspective
sketches. For example, they do not describe the shape of an object exactly
because of distortion at the corners, nor do they provide complete
information for the object to be made.
gure 3-21. In real life, objects at a distance seem narrower or shorter than they are close up.

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74
Technology: Engineering Our World
Sometimes you will want to add a piece. For example, you could make
a sketch of a box with a small block added to one side. This method of
isometric sketching may be used to draw a simplified house.
1. Lightly construct an isometric box eight squares long, four squares
wide, and six squares high, as shown in Figure 3-16.
2. Construct the basic shape of the house by removing a corner of the
box. Add lines for the roof. See Figure 3-17.
3. Add details, including windows and doors, as shown in Figure 3-18.
4. Complete the line work by removing unnecessary construction
lines. Darken the remaining lines to form the building’s shape. Add
color if desired. See Figure 3-19.
While isometric paper makes sketching easy, it has one disadvantage.
It leaves grid lines on the final drawing. These could confuse someone
looking at your drawing. Designers often prefer to sketch on plain paper.
To make a freehand isometric sketch of a rectangular block on plain paper,
use the method shown in Figure 3-20.
Perspective Sketching
Look at the photograph of the railroad tracks in Figure 3-21. Notice
that the parallel lines of the tracks appear to converge. The columns on the
station platform that are farther away appear shorter, and the platform
seems narrower at a distance. Of course, railroad tracks don’t converge,
columns don’t get shorter, and platforms don’t become narrower.
gure 3-16. To draw a house, make a box on an
isometric grid.
gure 3-17. Add and remove lines to shape the
house. See how points on the grid are used to draw
the roof lines.

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