Ellipse Construction, ContinuedThe trammelmethodThe trammel method of ellipse construction involves plotting a series ofpoints by using a strip of paper, cardboard, plastic, or straightedge markedwith two foci and rotating the strip up, down, and around horizontal andvertical axes. The strip or length of paper or cardstock is a trammel. Thetrammel has three marks, two representing the foci and one representing theellipse circumference.To construct an ellipse using the trammel method, use this table:Step12345ActionLay out horizontal (AB) and vertical (CD) axes that intersect atright angles (0).Determine the minor and major axes and the foci of the intendedellipse.On a strip of paper or cardstock, lay off distance GE representinghalf the length of the minor axis and GF representing half thelength of the major axis.Set the trammel on the drawing so that E is always traversing ABand F is moving along CD.As you move the trammel, plot points at G which will alwaysindicate the circumference of the ellipse.Figure 2-48 shows the position of a trammel as you construct an ellipse.Figure 2-48.—Thetrammel method ellipseconstruction.Continued on next page2-49
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