Makita has a small high speed grinder. it is great for doing the rough shaping after you band saw the window out. Then I use files,. Dremel and a long sanding board. I like to put a fairly large radius in the area between the window and the shelf. I need to d a build along on that someday. It is critical I believe in helping to eliminate the problems caused by compression which crack a lot of bows in the back of the shelf and sight window. I have a ball mill I carefully do the radius with on my dremel./ Steve