How do I rout a groove in an arch?

I want to build arched-top paneled doors. How do I cut a dado on the concave side of the curved top rail to accept the panel?
—Dick Rosenboom, Gainesville, Fla.

Pick up a slot-cutting bit for your table-mounted router, Dick. Slot cutters usually come in three parts—the arbor, a slot cutter, and a guide bearing—so that you can customize one to fit your cut. Choose a cutter to match your panel's edge thickness and a guide bearing that properly limits the depth of the cut.

To use the bit, remove the fence from your table, and set the bit height so that it is centered on the rail. Install a starter pin for leverage so you can ease the workpiece into the bit to start the cut, as shown. Then, simply guide the workpiece against the bit's bearing.