How to Make an Arch With Plywood

Measure the width you want your arch to be, using the tape measure. Then measure the depth you want your arch to be and add 2 inches to this measurement. Use these two values to draw a rectangle in the corner of the piece of plywood.

Measure 2 inches along the shorter side of the rectangle, then use a ruler to draw a line -- parallel to the longer side -- joining the two shorter sides. This is the header line.

Measure halfway along the longer side closest to the header. At the halfway point, draw a straight line -- parallel to the shorter sides -- connecting the two longer sides and continuing down the plywood board. This is the bisecting line. Where this line bisects the header is where the apex of the arch will be.

Tie a pencil to a piece of string and anchor the other end in the plywood with a nail. This will enable you to draw a curve when the string is pulled tight. Position the pencil on the apex of the arch and position the nail somewhere along the bisecting line below the rectangle on the plywood board. Begin drawing light curves with the pencil on a string. If necessary, remove the nail and position it higher or lower on the bisecting line, shortening or lengthening the string and altering the angle of the curve. When you are happy with your curve, draw a thick line in pencil along the full length of the arch and remove the nail.

Use a coping saw to cut out the rectangle from the plywood. Use a jigsaw to cut out the curved arch from the rectangle. Coat the plywood in wood primer. Allow it to dry and the arch is ready for painting and decorating.