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Re: Variable radius arched doorwayFrom: jncarr@nc.rr.com
Category: Architecture and Building Design
Remote Name: 66.26.59.235
Date: 25 Dec 2004
Time: 09:52 PM
CommentsA curve that starts with a small radius and gradually increases in radius until the center (then returns symmetrically to the small radius) is called an ellipse. Since this is an arched doorway, you actually will be using only half of the full geometrical figure called an ellipse. There are several techniques for creating an elliptical curve, but one of the easiest uses only three finishing nails and a piece of string or light guage wire. The trick is to locate the focal points of the ellipse, then let the string do all the work. First, decide how high you want the arch to be. The width of the ellipse is the width of the doorway. On a piece of Masonite or plywood draw a line the width of the doorway - this is line "W". Measure the midpoint "m" of this line and write it down - you'll need it later. At the midpoint of "W", draw a perpendicular line, "H" and on it mark a point the height of the arch "h". Now, lock your tape to "m" that you wrote down earlier, then extend it from point "h" on "H" to where your tape meets "W" on the left side of "H". You have now formed a right triangle with one side as "H" with dimension "h", the hypoteneus is your tape with dimension "m" and the other leg is on "W" with a newly constructed length. This is the first focus point. Repeat the process on the right side of "H" (or merely measure the distance from the center to the first focus and copy that to the right side). Now set a finishing nail at each of the two foci and at point "h", leaving 1/2 to 1 inch or so sticking out. Loop a piece of string around all three nails and tie it off with a secure knot. The total length of the string loop is very important, so it must be taut around the three nails. Now remove the nail at "h". Place a sharp pencil in the loop of string. Starting at "h" draw an arc by keeping the string taut and moving it from "h" to the left until it meets line "W". Make sure the pencil remains perpendicular to the template. Repeat the process to the right, again drawing from "h" to the line "W". You now have a perfectly formed ellipse. One tip is to notch the pencil wood just above the lead to keep the string from riding up or down as you draw. Also, light guage wire is sometimes preferred over string since it may not stretch as much. Cut the template out and use it for framing or marking on drywall.
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