Flat stones are essential to good sharpening. The Dia-Flat from Diamond Machining Technology (DMT) is certified flat to within .0005″ and makes quick work of flattening waterstones or oilstones.
I tried it out on a well-used Shapton ceramic stone, and was finished in about two minutes! (That’s pretty impressive, as Shapton stones are so hard that flattening them with sandpaper is impractical.) In fact, I had so much fun that I flattened every stone in my shop.
According to DMT, their Diamond Hardcoat Technology—utilizing precisely-sized micron mono-crystalline diamond—outlasts any other diamond-coated lapping plate. It’s 120 micron (roughly equivalent to 120 grit sandpaper) and can be used on any stone, from coarse to fine. The Dia-Flat’s generous size is another plus. The plate is 4-1/2″ wide by 10″ long, which is plenty large to flatten any stone. For the quickest results, use it under running water or in a tub of water. If you’re flattening oilstones, use oil instead of water.