The old furrows (Grooves from center to outer edge) were getting too wide due to years of dressing (Sharpening). So, I had to remove about 1/4 in. from the face of each stone. Then, cut new furrows. I used diamond blades and it took 3 weeks (It is fresh water quartz – harder than glass).
Course I have customers … etc. So, I didn’t work on them constantly. I laid out the same pattern of furrows that were in the stone originally. The red color on the stone is red chalk. I rubbed a straight edge over the stone and this marked the high spots for me to grind off. Once it was perfectly flat I gave both stones a slight taper to the edge and made sure the edge of the furrows were sharp. I managed to cut my hand once so I know they are sharp.
I am now making the best flour and cornmeal I have ever made. Theoretically I won’t have to do this again for another 50 years.