These are the most common of the non-circular gears. Left gear running constant, drives right gear at a variable speed depending upon the shape of the ellipse. Used in certain types of printing presses.
[Virginia Downward & William M. Clark, 1930]

[Editor’s Note: Aside from the technical applications, elliptic gears are a nice exercise in descriptive geometry. They also illustrate Reuleaux's theorem that the planar motions of any two bodies can be represented by pure rolling of two solid bodies. In this case the elliptic bodies are in pure rolling on the pitch line between the teeth and the center of rolling is at the foci of the two ellipses. These rolling surfaces are called 'centrodes' in modern kinematics theory. Clark copied this model from the 1868 catalog of mechanical movements by Henry T. Brown, Figure 33. FCM]

Francis Moon 2005-00-00