Ellipse Construction, Continued
The trammel
method
The trammel method of ellipse construction involves plotting a series of
points by using a strip of paper, cardboard, plastic, or straightedge marked
with two foci and rotating the strip up, down, and around horizontal and
vertical axes. The strip or length of paper or cardstock is a trammel. The
trammel has three marks, two representing the foci and one representing the
ellipse circumference.
To construct an ellipse using the trammel method, use this table:
Step
1
2
3
4
5
Action
Lay out horizontal (AB) and vertical (CD) axes that intersect at
right angles (0).
Determine the minor and major axes and the foci of the intended
ellipse.
On a strip of paper or cardstock, lay off distance GE representing
half the length of the minor axis and GF representing half the
length of the major axis.
Set the trammel on the drawing so that E is always traversing AB
and F is moving along CD.
As you move the trammel, plot points at G which will always
indicate the circumference of the ellipse.
Figure 2-48 shows the position of a trammel as you construct an ellipse.
Figure 2-48.—The
trammel method ellipse
construction.
Continued on next page
2-49
