I've been sharping blades for a few years now, i used to do it by filing them by hand but now that theres too many of them and too little time what is the best way. I know this guy who did them for me for free last summer and fall but sadly his health is not to good right now. I feel bad asking him so i need to start doing them again. I think he used a angle grinder with a metal sanding disc on it. Can anyone help me out on this one?