For the technically astute, DMT diamond stones are comprised of a perforated steel plate that is injection-moulded onto a glass reinforced polycarbonate resin base, in which are embedded precision sized micron diamonds in an electro-plated nickel matrix. In layman’s terms, this means you get the latest in sharpening technology: a precision-engineered stone that is absolutely flat (expect a surface tolerance of about 0.005″), and one that will never hollow or groove.
The DuoSharp, as the name implies, is a combination stone, with a different grit on each side. The stone I tested has a fine (600) grit on one side and a coarse (325) grit on the other (model #W250FC-NB). It measures a generous 4″ wide, 10″ long, and is 3/8″ thick. One of the first things I noticed, is that diamond stones cut very aggressively and produce a very consistent scratch pattern. This is due, in part, to the spacing of the diamonds on the plate, and also to the circular perforation pattern on the plate. The perforations create tiny reservoirs that hold swarf, reducing the tendency to clog. Liberal use of water flushes the swarf away. The stones come with a non-skid mat that worked well (I used it on a marble surface).
Because of the aggressive cutting nature of the stones, I found that you don’t have to apply as much pressure as with a waterstone. The coarse grit is excellent for reshaping blades and it also did a super job flattening the backside of a chisel. The fine grit produced an edge good enough to take to my 4000 waterstone. An added bonus of these stones is that you can also use them to sharpen your tungsten carbide router bits. I used the coarse side to flatten all my waterstones, a job I previously accomplished with coarse sandpaper (and a lot more elbow grease). I was very impressed with the performance of the DuoSharp, and would recommend it as a primary stone for reshaping and fine honing prior to finish sharpening with a 4000 or 6000 grit waterstone.
DMT DuoSharp stones come in 8″ and 10″ sizes of the following grit combinations: extra fine (9 micron/1200 grit) and fine (25 micron/600 grit); extra fine and coarse (45 micron/325 grit); fine and coarse; coarse and extra coarse (60 micron/220 grit). An optional stand is available (item B8250) and holds either the 8″ or 10″ stone.
By the way, DMT makes a wide array of sharpening products that use the monocrystalline diamond technology for just about any shop application you can think of.
The stones are competitively priced, considering that they should give years of use in a small shop (and probably a lifetime of use for the hobbyist). 8″ stones are available for about $120, and 10″ stones for $153. More information can be had at dmtsharp.com. Highly recommended as a general shop bench stone.