106 Section 1 Introduction to Drafting
Arc
An arc is a portion of a circle. Just as the
Circle
command automates the creation of a
circle, the
Arc
command automates the creation
of an arc, Figure 4-6. Most CAD software allows
you to select from several methods of defi fining
an arc. Examples include:
• Three points on the arc.
• Starting point, center, and endpoint.
• Starting point, center, and included angle.
• Starting point, center, and length of chord.
• Starting point, endpoint, and radius.
• Starting point, endpoint, and included
angle.
• Starting point, endpoint, and a starting
direction.
AutoCAD Example:
Command: arc↵
Specify start point of arc or [Center]: 0,–2↵
(or pick a
point on screen)
Specify second point of arc or [Center/End]: 0,2↵
(or
pick a point on screen)
Specify end point of arc: –2,0↵
(or pick a point on
screen)
Command:
Spline
A spline is a smooth curve that passes
through a series of points. Usually, the points
can be edited to change the “fit” of the curve fi
after creating the spline. This provides greater
accuracy for approximating irregular curves and
other shapes that are difficult to draw as arcs. fi
Splines are drawn with the
Spline
command.
There are two common ways to create splines,
Figure 4-7. One way is to pick or enter points to 7 7
establish control points along a curve. Another
method is to convert a series of existing lines
into a spline.
AutoCAD Example:
Command: spline↵
Specify fi rst point or [Object]: 2,3↵
Specify next point: 5,4↵
Specify next point or [Close/Fit tolerance] start
tangent: 8,3↵
Specify next point or [Close/Fit tolerance] start
tangent: ↵
Specify start tangent: ↵
(or pick a point to specify the
beginning direction of the curve)
Specify end tangent: ↵
(or pick a point to specify the
ending direction of the curve)
Command:
Ellipse
An ellipse is a closed circular object with
an oval shape. The arcs making up the shape
Figure 4-6. There are several ways to defi ne an arc.
Figure 4-7. Creating splines. A—Picking points to
establish control points for the fi t of the curve.
B—Creating a spline from connected lines.
A
B