Trim soundboard flush with sidesThe soundboard is left a little oversize when it is glued to the sides. This is just because the bandsaw that I use to cut out the soundboard can tear out little splinters. A factory would use a CNC router or a hand-held router and template to cut out the soundboard, but that isn't really necessary.
After the glue is dry, I usually trim off the excess with a sharp chisel. Back woods are usually much harder and I use a router to trim it the back. If the router happens to be set up for the back, I use it to trim the soundboard too.