Single virtual place where arch will be installed, measure the height and width of the opening and determine the height of the arch. Typically, the height is 10% of the width of your door or interior of the opening.
Take a sheet of plywood or drywall, draw a line equal to the width of the opening, which let's call A and B. Note on the segment AB the middle, this will be point L. Swipe through the midpoint perpendicular. This perpendicular will coincide with your the Central axis of the opening (point C).
Connect the points A and C, and divide the resulting cut AC in half, receiving a Swipe through point D. point D another perpendicular to the intersection of it with the axis of the opening. Put there point.
Draw a arc of radius EA. Swipe between AB and the semicircle line exactly in the middle, calling it N. The drawing is ready.
The radius of the circle arches on the school formula: R = (L2 +H2) / 2H. Calculating the radius of the arch and knowing its height of rise (width of the Board), go to the calculation of the maximum possible length of the part that will have to be cut out from the width of the Board. Perform calculation according to the following formula: L= √2RH - H2
You should know that in order to make your arch items should be slightly larger than that obtained in the calculation, as they will have each other to be joined, imposing on each other. Before you cut directly arched design, it makes sense to make a template and try it, you will avoid errors and get the pattern ready for cutting your material - wood or drywall.
There is a simplified version of the calculation. Note above the door the height of the arch and add to the mark of 5-7 cm You will get the height of the arched opening. If the resulting height is greater than the height of the door, you have to peck. But to build the scheme of the arch so that all the angles and the circumference was equal to have all the same using formulas.