Here are the basic tools I use . . .
Left: The Stewart System up top and Ellsworth Hollowing tools for larger work
Right: Ellsworth small hollowing tools and some homemade tools from allen wrenches
Note: You can also buy drill rod and bend (using a MAPP gas torch - Propane is not hot enough for much larger than 3/16") tools to your desired shape for undercutting . . . I'll take pictures and post as time permits