Max Alth - Sharpening hand tools

by Max Alth

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Alth, Max

Sharpening hand tools / by Max Alth
A Storey Publishing Bulletin, A-66
ISBN 0-88266-280-5

No doubt, the hammer was the first tool invented. Somehow, early man found that it was better to hammer things with a rock in his hand than with his fist alone, and the hammer was discovered. Later, man found that it was better still to fasten the stone to a handle, and the true hammer was born.

The sharpened edge was probably the second tool invented. One can knock a saber-toothed tiger to the ground with a hammer, but one cannot use a hammer to cut tiger steaks. At first, naturally sharp-edged shards of hard stones, such as flint and obsidian, were used for cutting. As the years went by, someone thought of putting edges on the stones, and man began to chip and knap (pressure chip). After only a few hundred thousand years, someone came up with the idea of improving the chipped edge by rubbing the sharpened edge with another stone. Sharpening was discovered and the Neolithic Age began. (Rubbing of stones is one major difference between the New Stone Age and the preceding Old Stone Age.)

It was not long after the invention of the sharpened edge that man learned that sharpness is not a permanent state. He probably learned it that same afternoon, when he tried to cut his second tiger steak. Thus, the art of sharpening was forced on early man and has remained a necessity ever since.

At first, sharpening was simply a matter of rubbing one stone against another. Then as metals and metal alloys were discovered, sharpening became a matter of rubbing a stone against a metal. When the metals became harder, man searched until he found stones especially suited to sharpening. In fairly recent times, synthetic sharpening stones were developed stones that are hard enough and abrasive enough to sharpen the hardest metals.

Today there are specific stones and stone shapes (as well as other tools) for properly sharpening every edged tool and every metal and alloy used for an edged tool. This bulletin will tell you the proper way to sharpen many common hand tools chisels, various types of knives, shears, scissors, tin snips, hatchets, axes, mauls, auger bits, and saws.

Proper tool sharpening is a precision craft. You will need a lot of practice before you will achieve consistently good results. Practice, experiment, ruin a few practice blades, even shed a few tears of frustration and then practice some more. Eventually you will master the craft of sharpening.

This bulletin will have much greater value for you if you watch the motions described here performed properly once or twice. Find someone who regularly sharpens tools a local farmer, fireman, meatcutter, trapper, or even a professional tool sharpener and watch how it is done. Then practice with this bulletin as your guide. And good luck!

No edge remains sharp with use. The edge dulls as the metal wears. The sharper the edge, the more quickly it wears, and the more often it requires sharpening to maintain an ultrafine edge.

Corrosion is another enemy of a sharp edge. Visible rust prevents a knife from sliding smoothly through the substance being cut. There is also invisible corrosion, which can be caused by fruit juices attacking the metal blade. This is why when you cut something acidic, even with a stainless steel knife, it is good practice to wipe the knife dry immediately afterwards.

Just how thick must an edge be to be considered dull? This is a matter of application. A sharp knife would be quite dull when used as a razor. Technically, when an edge exceeds 1/200 (0.02) of an inch, it is pretty dull; but in general a knife is too dull when it will not cut for you.

Ordinary steel is a mixture of iron and carbon. The more carbon, the harder the steel. The harder the carbon steel, the sharper the edge it can be given and will hold. Unfortunately, the harder carbon steel is made, the more brittle it becomes. Therefore, it is impractical to make an edged tool from the hardest carbon steel possible. For example, an ax made out of brittle steel would be very sharp, but you would lose a chunk of it the first time you hit a frozen knot or a stone. In addition, you would have a difficult time trying to hand-sharpen it in the field. Axes are, therefore, made from comparatively mild steel.

The solution to the problem of brittleness is toughness. This is the ability of a hard metal to give a little so that it does not break. Toughness is produced by tempering and adding exotic metals such as chromium, vanadium, molybdenum, tungsten, and nickel. Unfortunately, with the exception of nickel, all the exotic metals are expensive.

Stainless steel is made by the addition of chrominium and nickel. The stainless steels that hold the best edge depend almost entirely on chromium for their resistance to corrosion. The less expensive steels, which resist corrosion much better, contain the less expensive, softer nickel. The alloy found best for cutlery is the so-called 400 series of stainless alloys. The best in this series is 440-C which has a 17-percent to 19-percent chromium content.

Commercial cutlery used by professional butchers and chefs are straight-carbon blades made from an alloy of steel that is primarily carbon and iron. The mix contains 50 to 80 parts of carbon to 1,000 parts of iron. Less carbon makes for a steel that is easily dulled. More carbon makes for a steel that is easily nicked and difficult to sharpen. Add sufficient carbon and you get steel that is almost as hard as a diamond and just as brittle. In any case, without the addition of chromium and/or nickel, these straight-carbon blades corrode, stain, and rust. They must be kept dry or oiled.

The angle or bevel that forms the cutting edge of a tool is called its edge bevel. The edge bevel that you find on a tool (unless it has been altered by age or error) is that bevel best suited to the steel that makes up the tool and the way the tool is used. If you alter the edge bevel to make it longer and narrower, you weaken the edge. It will dull more quickly and chip more easily. If you shorten the bevel and broaden the angle, the cutting ability of the tool will be reduced. The angle formed by the edge bevels of common cutting tools ranges from 10 to 50 degrees. The sharper the angle, the better the tool cuts or slices, but the weaker the edge because there is less metal behind it. Here are some common edge bevel angles.