I don't bother trying to sharpen a dull blade anymore. It won't be a sharp as a new one. I do sharpen a new blade several times times during use with the vertical sharpener from Grace Co. It keeps the blade sharp for a long time. The date on my blade in my cutter says 11/13. It is still very sharp but I use my Go more then my rotary cutter. Of course if it gets a nick, it goes right in the trash.