How To Draw An Ellipse Using Concentric Circle Method

Trammel Method

An ellipse may also be drawn by the trammel

method. You will need your straightedge. On the

straight edge of a strip of material, mark half the

distance of the major axis, AO (fig. 14-27, view A).

Then, mark half the distance of the minor axis, CO.

Draw the major and minor axes on the drawing sheet.

Move the straightedge, keeping point A on the minor

axis and point C on the major axis. Using point 0 as

the guide, draw the ellipse as shown in view B.

Concentric-Circle Method

The concentriccircle method of drawing an ellipse

is the most accurate of the methods discussed in this

section. However, you must be able to handle your

instruments accurately. As you read this section, refer

Figure 14-26.--Drawing an ellipse using a pin and string.

to figure 14-28.

1. Draw the major and minor axes.

Pin-and-String Method

2. With the intersection as a center, draw a circle

that has the major axis as a diameter. Then,

The easiest method of drawing a large ellipse is the

draw another circle with the minor axis as the

pin-and-string method. To use this method, refer to

diameter (view A).

figure 14-26 and use the following steps:

3. Draw several radii from the center to the arc of

1. Draw the major and minor axes.

the larger circle (view B).

2. Set the dividers to one-half the length of the

4. Wherever these lines cut the smaller circle, draw

major axis. Using one end of the minor axis as

short horizontal lines outward from the arc of

a center, draw arcs intersecting the major axis.

that circle.

Points F and F are the foci of the ellipse (view

5. Wherever the radii touch the larger circle, draw

short vertical lines to intersect the short

3. Drive pins at the foci and at one end of the minor

horizontal lines (view C). The points where

axis. Tie a cord around the three pins, as shown

these short horizontal and vertical lines intersect

in view B.

define the ellipse.

4. Remove the pin at the end of the minor axis, and

6. Use the French curve and draw the ellipse from

place a pencil or pen inside the loop. Keep the

these plotted points (view D). The French curve

string taut and draw the line of the ellipse.

Figure 14-27.--Drawing an ellipse using the trammel method.

14-16