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The Woodwright's Guide: Working Wood with Wedge & Edge By Roy Underhill
Trammels and the Ellipse
When the arena for displaying the cabinetmaker’s mastery of wood is an oval, out comes the ellipsograph. There’s no doubt about what an ellipsograph does, but how it does it — that takes some thinking. The device is also called a trammel, a bit confusing since trammel points are the spiked heads used to make up a beam compass. These look like pieces from an ellipsograph that lost their X. They just make circles.
You can also generate ellipses with two nails and a string. Draw a long axis line down the center of the length of the tabletop and a short axis line across the width. Measure half of the long axis, then measure the same distance from an outside edge of the short axis to make intersections with the long axis. Tack nails into both of these intersections and into the outside edge of the short axis. Now tie a snug string around these three points and then pull out the outermost nail. Set a pencil within this loop of string and bring it around to trace a perfect ellipse within the rectangle.
The ellipsograph and the nail-and-string method can generate ovals of any size, but the latter is better suited to larger tabletops.
"The Woodwright's Guide: Working Wood with Wedge & Edge" By Roy Underhill
© 2012 The University of North Carolina Press