In my work as a trim carpenter, I'm occasionally asked to assemble the blocking for coved wall-to-ceiling intersections or arched doorways that will be finished in plaster or drywall. Laying out radiused blocking is simple; it's just a portion of a circle. If the curve is to be part of an ellipse, though, it gets trickier. Unlike a circle, an ellipse has two focal points. There are several methods for drawing ellipses using strings or graph paper. The simplest I've come across is the one illustrated here.
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