163
Basic Geometric
Constructions
6
Learning Objectives
After studying this chapter, you will be able to:
Use manual drafting tools and methods to
make geometric constructions.
Use CAD commands and methods to make
geometric constructions.
Draw, bisect, and divide lines.
Construct, bisect, and transfer angles.
Draw triangles, squares, hexagons, and
octagons.
Use special techniques to construct regular
polygons.
Construct circles and arcs.
Technical Terms
Arc
Bisect
Center
Chord length
Circle
Diameter
Equilateral triangle
Hexagon
Hypotenuse
Irregular curve
Isosceles triangle
Octagon
Pentagon
Perpendicular
Polar coordinates
Polygon
Radius
Rectifi length fied
Regular polygon
Right triangle
Square
Tangent
Engineers,
architects, designers, and
drafters regularly apply the principles of geom-
etry to the solutions of technical problems. This
is clearly evident in designs such as highway
interchanges and architectural structures,
Figure 6-1, and in machine parts, Figure 6-2.
Much of the work done in the drafting room
is based on geometric constructions. Every per-
son engaged in technical work should be famil-
iar with solutions to common problems in this
area. Methods of problem solving presented in
this chapter are based on the principles of plane
geometry. However, the constructions that are
discussed are modified and include many spe- fi
cial time-saving methods to take advantage of
the tools available to drafters. This chapter cov-
ers both manual (traditional) and CAD methods
used to make geometric constructions.
Accuracy is very important in drawing
geometric constructions. A slight error in laying
out a problem could result in costly errors in the
fi nal solution. If you are using manual drafting fi
tools, use a sharp 2H to 4H lead in your pencil
and compass. Make construction lines sharp and
very light. They should not be noticeable when
the drawing is viewed from arm’s length.
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