Now that the exterior curves are established, it is time to hog out the concave back and make it thin enough to vibrate well. It begins as a drill press job.
I use a Forstner bitt with the center point filed down so that it protrudes just a tiny amount past the cutters. The drill press is set to stop about 3 16ths above the top of the post. The post top is padded with a piece of cork to avoid denting the top of the workpiece.
Now, one hole at a time , I hog out the excess wood.
It takes a little time, and makes a bit of a mess, but you remove a lot of wood this way.
Then, with a 36 grit sanding disc, you smooth everything out until the little holes left by the point of the Forstner bitt disappear. Then you know you are about at the thickness you desire.
Here is the back for Holey Moley. I will clean up a bit around the edges with a scraper, but it is pretty much where I want it. It started as the end of the thick plank it now sits on.