Hawg, you are right (as per usual!) about circular saw blades. They are easier than a file; Those things take a loooong time a grinding! When I made the file blade, I started out grinding, but the thickness of the file was taking forever to grind. I heated it red hot and plunged it in a bucket of asbestos powder (GASP!!!) that was setting around at work. That's how long ago I made that knife! Now, I use a trash can with wood ashes in it to cool steel down slowly. The lawn mower blade wasn't quite as bad as the file but thicker than a saw blade for sure. Some other stuff to consider is heavy grass shears or shears of any kind and old carbon steel butcher knives that can be ground to a new shape.
