If you want all the pieces (as in a bisected Nautilus), or if the shell is very large, you will need some kind of saw - I don't know the details. However, if the shell is not huge, and you just want a center slice for display, and don't need the rest of the shell, the easiest way to do it is with a belt sander. Just use a coarse sandpaper to grind away the parts you don't want. It only takes a few minutes. Then smooth off the two sides with a fine sandpaper. You should wear a particle filter (as used in spray painting - available in hardware stores) to avoid breathing the shell dust that is produced. Paul M.