208 Section 2 Drafting Techniques and Skills
Calculate the
Circumference of a
Circle Using the List
Command
CAD
List
command provides a quick way to
t
determine useful data about drawing objects.
The data displayed depends on the type of
object selected. After entering the command and
selecting an object, a window is displayed with
dimensional data. To identify the circumference
of a circle, enter the
List
command and select the
t
circle. The data listed includes the circumfer-
ence, radius, area, and center point location.
Figure 6-60. Laying off the rectifi ed length of an arc. A—Using the construction method. This method is accurate
to .1%. B—Using the equal chord method. This method is not as accurate as the construction method. C—There
are many applications for this construction in drafting. Shown is a “stretchout” development of a sheet metal part.
E
A B C
B
A
C
D F H
Application
G
Using the Construction Method
1. Arc AB and the center of the arc, Point E,
are given, Figure 6-60A.
2. Draw Chord AB. Extend the line and
locate Point C so that Line CA is equal to
one-half Line AB.
3. Draw Line AD tangent to Arc AB at
Point A and perpendicular to Line EA.
4. Using Point C as the center, strike an
arc with a radius of Line BC to intersect
Line AD. The length of Line AD is the
Lay Off the Length
of an Arc
approximate length of Arc AB. The error
for this projection is less than 1″ in 1000″, ″
or .1%, for angles up to 60°.
Using the Equal Chord Method
1. Arc FG is given, Figure 6-60B.
2. Draw Line FH tangent to the arc. The
length of this line should be an estima-
tion of the rectifi ed length. fi
3. Using dividers, divide Arc FG into an
equal number of chord lengths. The
accuracy of this projection is increased
when a greater number of chords is used.
4. Lay off the same number of chord lengths
along Line FH. The length of Line FH is
the approximate length of Arc FG.
An application of this construction is
determining the “stretchout” length of a sheet
metal part, Figure 6-60C.
Calculate the Length
of an Arc Using the
List Command
CAD
List
command can be used to quickly
determine the length of an arc. After entering
the command and selecting an arc, data listed
for the arc includes the length, radius, center
point, start angle, and end angle.