I use a flat file if they are really dinged up, then a sharpening stone to finish them off. Just need to put an edge on them the same angle as they had. I usually sharpen once...then order a new set anyway, but it can be done with a small file and stone. It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com