For wooden electrical plates, I strongly suggest placing a thin layer of steel behind the switch. It might even be code to do so. I've made dozens of switch and outlet covers out of oak. They turned out great. For the metal backing, I bought a bunch of cheap metal covers and trimmed them down with tin snips. I had no problem holding down the 3/8" material I used to make them. The wood was old recycled stair treads so very dry and stable. If you're using fresh cherry, I suggest getting it close to dimension and letting it air dry for at least a week, then finalizing the dimensions before using in the CNC.

PXL_20201218_170706642.jpg