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I Forge Iron

To Draw an Ellipse


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To draw an ellipse you need to know the width AB in the drawing and the length CD in the drawing,

You lay these out (draw them) on a piece of posterboard or other medium. Fig 1

You can use a piece of string tied together as in Fig 2

You use a pencil inside the string with the string around the 2 points P.

To find these points P, there is a very complicated algebra formula, or you can just use a compass set the distance from where AB and CD cross in the middle to either C or D, then scribe an arc on either side of line AB using A as the common point to swing the arcs. Where these 2 arcs intersect line CD are points P.

Using thumb tacks sticking out from the front side at both points P and point A, tie the string so it is tight around these 3 points. Fig 2

Remove the tack at point A, and using a pencil held tight against the inside of the string, draw the ellipse keeping the string taunt (tight) all the way around.
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