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We are going to buy some flexible crown molding to go around a curve that follows the main staircase in the foyer.
The manufacturer needs to know the radius of the curves. How do I figure that out?
The whole doesn’t curve, just the two corners that follow the staircase. In between the 2 curved corners is a flat wall (front door below) with a window in it.
Replies
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Dee Vee, here are some hints:
Definitions:
* Radius (R) - a straight line from the center point of a circle to it's perimeter
* Arc (S) - a segment of a circle
* Chord (C): a straight line segment that intercepts a circle at two points.
Given: a circle = 360°
Pi = 3.141592
Area (A) of a circle = Pi R2
Solution: Find "R"
Dano
*DeeVee.Try this.Draw 2 chords on the arcs. one end of each chord at the end of the arc. The other end of each chord at the mid point of the arc.Now erect a line 90 degrees to each chord at its mid point.Where these lines intersect is the center of the circle represented by the arcs.No math required.I doubt that you will find this construction to be a true circle,however the moulding being flexible,This radius should be close enough. I wish that I could post a sketch.Mebby some day. ¬¬¬¬¬¬¬¬¬PAT¬¬¬¬¬¬¬¬¬
*The problem is not determining the radius from a drawing but from a real life wall. The center of the circle is somewhere in the middle of the air. Try this. Determine the end points of the arc. Stretch a string between those 2 points and measure the length. At the same time measure the maximum distance perpendicular from the string to the arc (this occurs at the centerpoint of the string). Extreme accuracy is not needed if the molding is somewhat flexible. If "C" is the chord length and "x" is the distance from the arc to the string then R (the radius) is ((C/2)^2 + x^2)/2x.For example, if C=60 inches and x=12 inches then R=43.5 inches.
*Ben,Yes, that's why I provided the "hints".
*Thanks for the hints and equations! I could not remember anything from my geometry and math classes!
*In my daughters house, that they built about 3 years ago, a finish plasterer came in and did the crown in the curved stair case out of molded plaster. Looks damn good to me.
*We can't afford molded plaster, but we've left what original molded plaster we could that wasn't damaged by water.
*Major,I too have used that method when dimensions are not critical. I've attached a sketch.Best,Seth
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