formula for finding the radius of an arch
The formula for finding the radius of an arch is
R=h÷2 + w•w÷8h where h=height from chord line to the highest point of the arch and w= the width of the distance where the chord intersects the arch.
For example, if you wanted to trim an arch window that is 48" wide with an arch that is 6"high the following would figure the radius:
6÷2=3 so 3+ 48squared ÷6(8)
51" is the radius which can be traced using the simple expedient of a 51" piece of string, a central pivot point and a pencil attached to the string. Measure exactly 51" from the point where your pencil touches and pivot off of that point. Easy.
This formula always works, you can even create a calculator for figuring radius of arches so that all you need to do is plug in numbers. They are readily available on the web too, so long as you know the formula is for figuring the radius of an arch. As long as you can cut along the line you have drawn, it will fit perfectly. Hope this helps, I have always liked math, it has made me more efficient than anything else I have learned or been taught.