Trammel of Archimedes - GIF

Trammel of Archimedes is a mechanism that generates the shape of an ellipse.

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Previously:

https://www.homemadetools.net/forum/...652#post186163
https://www.homemadetools.net/forum/...905#post198704
https://www.homemadetools.net/forum/...753#post155933
https://www.homemadetools.net/forum/...841#post175270
https://www.homemadetools.net/forum/...400#post116801

Mathematically, an ellipse is the locus of points such that the sum of the distances to two fixed points is a constant. If you only need to draw one or two, utilizing this definition is simpler than the admittedly elegant trammel shown.

https://www.youtube.com/watch?v=Et3OdzEGX_w

In my drafting classes many years ago we learned to draw an "ellipse" with a triangle and a compass. It was acknowledged that it wasn't 100% accurate, but it was close enough.