Chapter 7 Computer-Aided Drafting and Design
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trimmed automatically when the chamfer is
drawn.
Trimming and Extending Lines
Many objects in a CAD drawing are made
up of lines. During the drawing process, it is
sometimes necessary to “clean up” areas of the
drawing where lines must intersect accurately.
Trimming is useful when two lines overrun
past a corner. Extending is useful when a line
must be lengthened to meet an edge or other
entity.
The Trim command is used to trim lines,
arcs, and circles. After entering the command, a
cutting edge must be specifi ed. This represents
the point to where the object is trimmed.
Next, the object to be trimmed is selected.
The portion of the object extending past the
cutting edge is automatically removed. When
using the Trim command, you can select as
many cutting edges and objects as needed to
complete the trim operation.
The Extend command is used to extend
lines and arcs to meet other objects. After
entering the command, a boundary edge must
be specifi ed. This represents the point to where
the object is extended. Next, the object to be
extended is selected. The object is then extended
to the boundary to create a larger entity. As
mirrored are fi rst selected. Then, a mirror axis
is specifi ed. The axis represents a line about
which the objects are “refl ected.” The command
sequence typically allows you to keep or delete
the original objects selected before mirroring.
Creating Rounded and
Angled Corners
Rounded and angled corners are often
drawn in mechanical drafting. A round is an
arc representing an outside rounded corner. A
fi llet is an arc representing an inside rounded
corner. See Figure 7-20. A chamfer is an angled
line drawn where two straight lines would
normally meet at a corner. Rounds, fi llets, and
chamfers are used to smoothen sharp edges.
See Figure  7-21. Rounds and fi llets can be
drawn with the Fillet command. After entering
the command, the fi llet radius is set. Then, the
two lines, circles, or arcs forming the inter-
section are selected. The original objects are
then trimmed and the arc is automatically
drawn.
A chamfer can be drawn with the Chamfer
command. After entering the command, the
chamfer distances from the two lines to the
corner are set. A 45° chamfer is created with
equal distances. Next, the two lines are selected.
As with the Fillet command, the lines are
Original objects Objects after mirroring
(0,0)
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Figure 7-19. Mirroring an object creates a mirror copy
about a mirror axis. In this example, the original image
is mirrored twice using the X and Y axes.
Fillet
Round
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Figure 7-20. Fillets are used to strengthen inside
corners and rounds are used to remove sharp edges.
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