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The trammel method

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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



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