How to Choose a Sharpening Stone, Part 3: Diamond Stones

See our previous posts on how to choose a sharpening stone.

diamond stones

Diamond stones

Similar to the other types of stones, diamond stones come in different grits. One thing to keep in mind with all sharpening stones is that the Japanese grit system is different from the American grit system. So when I talk about an 8,000-grit water stone, it’s different from a 1,200-grit diamond stone. The best way to differentiate between the grits is with microns, but that can get a bit technical. (As I mentioned in a previous post, Chris Schwarz wrote on this and published a chart by Bert Bleckwenn on micron differences.)

I use what I simply refer to as coarse, medium, and fine diamond stones. The manufacturer refers to them as coarse, fine, and extra fine. The coarse one is about a 300-grit (American system equivalent.) The medium one is a 600-grit and the fine one is 1,200-grit.

I prefer the diamond stones that are a metal plate with the diamonds over the entire surface, rather than the kind that you can buy with the little holes in them. The substrate to that is usually rubber, and never perfectly flat. There are two brands that I would recommend. E-Z lap makes a good one as well as Dia Sharp by DMT. I prefer the DMT because they are thicker. DMT also makes one of the above-mentioned stones with the holes in it, but I would stay away from that kind. Get the kind that is a solid surface. The size stones I like are 3″ x 8″. As shown in the pictures, my diamond stones are thin and come in a handy bench-hook like holder.

diamond stone 5

Diamond stone flatness

The advantage of the diamond stones is that they are flat and stay flat; you don’t ever have to flatten them. That’s a big advantage for me. So when I’m sharpening, I don’t ever have to worry about flattening my stones. I can just go from my work on the bench right to the sharpening station, sharpen my chisel in two or three minutes, and get right back to work. On the other hand, if I used the water stones, I would have to flatten the stone, sharpen the chisel, clean up the watery mess, and all that good stuff.

The downside to the diamond stones is that they don’t refresh themselves. So when you sharpen, you’re actually wearing away the diamonds. After several years, the diamond stones will wear out, and you pretty much have to throw them away. However, they will last for several years—especially if only one person is using them in the shop.

The other downside that I’ve found with the diamond stones is that the grit doesn’t go as high as I’d like it to go. As I mentioned, my finest diamond stone is 1,200-grit, which I believe is equal to about nine microns. Up from there, some manufacturers do sell an 8,000-grit diamond stone, but I haven’t been very happy with that one in using it.

Next post: What I Use.

Frank Strazza

See our sharpening stones video and full sharpening video course.

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