This is a Google Sketchup drawing of picture frame stock made from cove molding that I have made on my radial arm saw. No special cutters are required.
Step 1: Basic setup of the saw
A cove cut pushes the work piece into the side of the blade rather than the front edge and reproduces the circular profile of the blade in the workpiece.
Cove cuts can be made on a table saw. Here you see the basic setup on a radial arm saw. The workpiece is guided by two fences with one on each side of the workpiece. The two fences blend into the background in the photo, so I outlined their working edges with red lines.
In order to achieve a smaller radius cut, I used the 7 1/4 inch blade from my circular saw rather than the usual 10 inch blade normally used on my radial arm saw. The motor is tilted to about 45 degrees so the teeth bite into the wood more easily as it is pushed toward the saw. Notice that the motor has also been rotated clockwise a few degrees (as viewed from above the motor) so that the yoke is no longer fully in the crosscut position. The spoon handle lever that locks the yoke (yellow arrow) was loosened to allow the motor to rotate and is again locked to hold the motor in position.