This is our fifth newsletter and we continue to strive not only to bring specials, but also interesting information about the knives as well. In the September newsletter we introduced
Shun Kitchen Knives from KAI. Shun kitchen cutlery could be the best kitchen cutlery available today. We are extremely proud to offer these fine knives. This month we are going touch a little on sharpness testing.
There are two schools of knife sharpening - those who like a knife to keep some roughness from the stone and those who believe that it should be as smooth as possible.
Both approaches have their benefits. Blades with a rough edge can be aggressive cutters, especially when the blade is thin. They have micro-serrations that act like a microscopic saw. These micro-saws are very well suited for slicing fibrous material, such as a rope. This edge is easy to produce because you just stop sharpening after a medium stone (200 to 300 grit). Blades sharpened this way do become dull faster as the points wear or bend, so frequent touch-ups are needed.
Smooth edges are best for cutting with a straight push and are preferred by barbers, surgeons and woodworkers. Research done by John Juranitch of Razor Edge Systems (1) shows that butchers can cut more meat per shift and tire less when using a smooth edge. Analysis with an electron microscope (2) has confirmed that wood cutting ability is correlated to edge smoothness. Sharpening a smooth edge requires more work, but the results are worth it. To be sure you are improving your sharpening; you need an objective way to test the results. Tests evaluating sharpness range from cutting silk to chopping trees. What you need is a test method that are useful in your workshop as you are sharpening. A major knife maker tests sharpness on nylon paint brushes. Most people test an edge by rubbing their thumb lightly across the edge and feeling how the edge grabs as it tries to cut into the thumb pad. To keep your thumb calibrated, test a known sharp edge like a new razor blade periodically.
Shaving hair on your hand or arm is another common sharpness test. Shaving sharpness can be achieved even on heavy hunting knives or an axe. I own a hunting knife that will shave even though the edge angle is a rather blunt 30 degrees. I use the term shaving sharp to describe this degree of sharpness and razor sharp to describe even greater sharpness. Razor sharpness is comparable to a razor blade and will literally pop the hairs off your hand or arm. Razor sharpness is only possible with both a polished edge and a small edge angle.
Testing by shaving can be misleading if the blade has a burr or wire edge. Steel naturally forms a burr - a thin bendable projection on the edge - during the sharpening process. A blade with a burr will shave but will not stand up to hard use. To test for a burr, slide your fingertips lightly from the side of the blade over the edge. You will feel the burr drag against your fingers. Test from both sides, because burrs are usually bent over one way or the other. As your sharpening improves you will be looking for smaller and smaller burrs. Many good sharpeners have learned to see a dull edge. Hold the blade in front of you with the edge in line with a bright light. Move the blade around a bit. A dull edge will reflect a glint. Nicks and burrs will also cause glints. When the blade is sharp these glints will be gone. (Material courtesy of "
Sharpening Made Easy")
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