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How to Draw an Ellipse with String

This Old House General Contractor Tom Silva shows host Kevin O’Connor an easy method for drawing accurate, smooth ellipses.

Tom Silva and host Kevin O’Connor meet back at the shop to discuss drawing ellipses. After showing Kevin a jig he built, Tom gives him a quick lesson on how to draw perfect ellipses with just two nails, a string, and a pencil.

How To Draw an Ellipse

Drawing accurate ellipses can be tricky, as they often come out uneven or slightly lopsided. However, if you need to draw a quick ellipse to make a template or guide, this method will help.

  1. Lay the workpiece out and draw a straight line in the center of the board. Also, use a utility knife or pocket knife to cut a small kerf near the base of the pencil (toward the tip).
  2. Lightly drive two nails into the workpiece along the line. Spacing will determine the shape and size of the ellipse, so this may take some experimenting.
  3. Tie a knot on one end of the string and place it over one of the nails. Loop the other end of the string around the other nail. Adjust the string’s length, so the ellipse reaches the desired height, and then wrap the rest of the string around the nail and tie it securely in place.
  4. Loop the string around the pencil’s kerf and slowly pass the pencil along the workpiece, starting outside of one nail and ending outside of the other nail. Flip the string over to the other side of the nails and repeat. This should result in a perfect ellipse.
  5. While the ellipse may be perfect, it might not be the perfect size or shape. Adjust the nail spacing or string length to tailor the size and shape.

Resources

Measure out your center line and place a nail at each end of the line leaving a little space outside. Wrap your string around the nails but stretch it up to where you want the top of the ellipse to be before securing the string to the nail. Using a notched pencil, set the string into the pencil notch, keep the pencil straight with tension on the string, and bring the pencil up and around to create your ellipse.

You can find all the materials at local home centers.


Materials

Tools