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Drawing an ellipse with string and pins

This is the step-by-step, printable version. If you PRINT this page, any ads will not be printed.

See also the animated version.

After doing this Your work should look like this
Start with the height and width of the desired ellipse. The two lines are the major and minor axes of the ellipse. The major axis is the longer one. Geometry construction with compass and straightedge or ruler
1.  With the compasses' point on the center, set the compasses' width to half the width (major axis) of the desired ellipse.

(This is called the ellipse semimajor axis).
Geometry construction with compass and straightedge or ruler
2.  Move the compasses' point to one end of the minor axis of the desired ellipse and draw two arcs across the major axis. Geometry construction with compass and straightedge or ruler
3.  Where these arcs cross the major axis are the foci of the ellipse. Label them F1, F2. Geometry construction with compass and straightedge or ruler
4.  Put a pin in each end of the major axis (they will be moved later), and tie a string to them so that the string between them is taut. The best way to do this is to push the pin through the string itself if possible, rather than tying a knot. Geometry construction with compass and straightedge or ruler
5.  Leaving the string attached, move the pins to the focus points F1, F2. Put a pencil point against the string and pull the string taut with the pencil. Geometry construction with compass and straightedge or ruler
6.  Keeping the string taut, move the pencil in a large arc. The pencil will draw out the desired ellipse. To avoid the string catching on the pins, you may find it better to draw the upper and lower halves of the ellipse separately. Geometry construction with compass and straightedge or ruler
7.  Done. The ellipse will pass through the four initial points defining the ends of the major and minor axes. Geometry construction with compass and straightedge or ruler

Other constructions pages on this site

Lines

Angles

Triangles

Right triangles

Triangle Centers

Circles, Arcs and Ellipses

Polygons

Non-Euclidean constructions