I would like to hollow-out the backside of a mantle board, and I'm trying to think of the best way to do it. I have various tools at my disposal, or can procure a needed tool.
The purpose is to hide various cords. Ideally, the hollowed section would be 4-6" deep and not noticeable from the sides.
My current thinking is to use a handheld plunge router with a bit at least 4" long and many shallow passes. Would a spiral upcut bit be best? Or would a double flute bit be better? Perhaps the router is the wrong way to go.
What is the best tool (and cutting attachment) for this task?