I took the slick I have now to a machinest. He flattened the back, and the front, on a liquid cooled surface grinder. In the future, I'll do it myself, as I don't like perfectly flat tools. I have a belt sander that I've clamped upside down to a sawhorse. Put your fingers on the back as you grind, and when you feel any heat, dip in water. It still takes awhile, but it's faster than the DMT stones. I've also used a flap wheel type disc on an angle grinder. Again, watch the heat.