Diamond stones are one of the newest developments in the field of sharpening. Although diamonds have been used for years in industrial applications, it's only been in the past few years that "a girl's best friend" has become a practical answer to sharpening tools in a home shop.
We've been using diamond stones (made by Diamond Machining Technology) for about a year now. During that time we've discovered they perform beautifully in some respects, and rather poorly in others.
Diamond stones cut extremely fast, faster than any other stone we've used (including Japanese water stones). And if you really need to hog off some metal, (without the problems associated with a grinding wheel) diamond stones are the fastest method we've found.
However, on the other side of the coin, I've been rather disappointed that even the "fine" stone doesn't produce a very fine cut. In fact, it's coarser than "coarse" oil stones, and I don't even consider using diamond stones when it comes time to hone a finished edge.
So what good are they? Diamond stones are ideal for the initial (coarse) honing needed to flatten the backs of chisels and plane irons. In Woodsmith No. 20 and 23 we talked about the process we use to sharpen these tools. In both cases the face (flat) side must be honed to remove grinding marks (left by the manufacturing process) and to take out any warp across the width of the chisel or plane iron.
This is a tedious job that often requires removing quite a bit of steel. Diamond stones excel at this kind of honing because they cut very quickly (which is very helpful when you're trying to correct a badly warped plane iron).
But what makes a diamond stone cut any better than a coarse India (aluminum oxide) or Crytolon (silicon carbide) stone?
Two things. First, diamonds are the hardest natural material known to man. And second, diamonds are crystaline (which produces sharp corners).
This doesn't sound like a big deal, but there's a definite advantage to using an abrasive that's both extremely hard and very sharp. The extreme hardness allows diamonds to retain their sharp cutting edges, rather than rounding over or breaking off as they're used.
And since diamonds remain sharp, they maintain a favorable rake angle. That is, since the sharp cutting points on diamonds don't round-over, they continue to cut the metal, rather than "plow through" or
"mushroom in" as other abrasives do as they get worn.
In fact, you can actually feel this cutting action as you use them. Without much pressure at all, you can feel the "drag" as the diamonds cut through the steel. (Water is used as a lubricant on these stones to carry away the shavings.)
This kind of rapid cutting action provides one of the best wrays we know to flatten chisels and plane irons. And if you don't have a grinder (or don't want to risk a "burned" edge), diamond stones are very helpful for "cutting" the initial bevel along the cutting edge.
Although both of these uses are only the initial steps in sharpening (honing and polishing on "normal" oil or Japanese water stones comes next), it's a step that's critical if you want a straight, sharp edge.
Howrever, the key in this whole thing is using a stone that's flat and that stays flat. This raises some questions about the w-ay diamond "stones" are manufactured. So we decided to go straight to the source: David Powell, President of Diamond Machining Technology (DMT) for some answers.
During our conversation, he confirmed our suspicions that diamond stones are a "high tech" product developed from the ground up, or in this case, the base up.
DMT uses fiber reinforced poly-carbonate to form the base. By adding fibers to the poly-carbonate, the tensile strength is increased to the range of mild steels, making it almost impossible to break the base.
After the base is formed, it's molded to a perforated steel plate. This plate is then ground perfectly flat to provide a true surface for applying the diamonds. (The polka-dotted appearance on the surface of the stones is created by the poly-carboante base showing through the perforated steel plate.)
Next, the diamonds are applied to the steel plate in a two-step process. (Both steps are actually carried out simultaneously). First, the diamonds are salted over the plate (with a coverage of about 80,000 diamonds per square inch.) As the diamonds are applied, a thin layer of nickel is electroplated to the surface of the plate to hold the diamonds in place.
This process continues until two-thirds of the height of the diamonds is submerged in the nickel. The result is that only the very tip of each diamond sticks above the surface of a very flat plate.
And since diamonds are very hard and durable, they will actually fall out before the surface becomes dished. Luckily, the w-ear rate for diamonds is so slow that the stones will last (and stay flat) for an incredibly long time.
Okay, diamond stones sound great, but they also sound expensive.
Granted, these stones aren't cheap. DMT offers five sizes (from 3" to 12" long), in both fine and coarse grits. The price ranges from $14 to $95. (The stone we use the most is the "fine" grit 2" x 6", $36.)
For more information on DMTs line of diamond stones, contact: Parkers, P.O. Box 241, Wellesley Hills, MA 02181. They will send a price list and mail-order form.
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There are a lot of things that either needs to be repaired, or put together when youre a homeowner. If youre a new homeowner, and have just gotten out of apartment style living, you might want to take this list with you to the hardware store. From remolding jobs to putting together furniture you can use these 5 power tools to get your stuff together. Dont forget too that youll need a few extra tools for other jobs around the house.