200 Section 2 Drafting Techniques and Skills
Construct a
Circle or Arc
of a Given Radius Tangent
to a Straight Line and a
Circle
CAD
Using a Compass
(Manual Procedure)
1. Line AB, Circle O, and Radius R are
given, Figure 6-51A.
2. At a distance equal to Radius R, draw
Line CD parallel to Line AB, Figure 6-51B.
Line CD should be located between
Line AB and Circle O.
3. With a compass, strike Arc E to intersect
Line CD. Use Point O as the center and a
radius of R + ro (where ro is the radius of
Circle O).
4. The intersection of Arc E and Line CD is
the center of the required tangent circle
or arc, Figure 6-51C.
An application of this construction is shown
in Figure 6-51D.
Figure 6-51. Constructing a circle or an arc of a given radius and tangent to a straight line and a circle. There are
many applications for this construction in drafting.
O
R
A B
A
O
ro + R
C
E
D
R
A B
B
R
R
Application
A B
C D
Using the Tangent, Tangent,
Radius Option (CAD Procedure)
1. Line AB, Circle O, and Radius R are
given. Refer to Figure 6-51A.
2. Enter the
Circle
command and enter
the
Tangent, Tangent, Radius
option. To
specify the fi rst tangent point, move the fi
screen cursor toward Line AB and pick
when the object snap icon appears. To
specify the second tangent point, move
the screen cursor toward Circle O and
select it in the same manner.
3. Enter the given radius. The required
tangent circle is drawn. If you need to
trim a portion of the circle to complete a
tangent arc, use the
Trim
command. Refer
to Figure 6-51C. Enter the
Trim
command
and select Line AB and Circle O as the
cutting edges. Then, select the portion
of the circle that lies outside the two
intersections.