By Roy, 2001
I got to thinking recently as Billy and I were having an exchange about edges and grinds of knife blades and how those manufacturing processes ultimately lead to the fit and pleasurable/efficient use of a knife. Well, at the time I was involved in organizing an ice (figure) skating competition. So, my mind was frequently drifting to images of other kinds of grinds and edges; those on ice skating blades to be exact. Well, now you’re wondering what this has to do with knives. Actually there is a pretty close connection in a real physical sense (just let your mind go, and think how knife blades work). Both knives and ice skates have metal blades and in order to function properly, it is best if they are properly ground, honed and sharpened for the task. Knives cut things like wood, leather, animal hide, etc. with their one sharpened edge. Ice skate blades, when properly sharpened, can cut ice with two edges (normally one at a time). What I will describe refers to figure skates----speed skates and hockey skates have their own separate edge configurations.
Imagine a piece of 3/16” steel (of uniform thickness, not ground to a lesser thickness at the cutting edge) attached to the bottom of your shoe or boot with the edge scribing a convex curve (the amount of curvature is called ‘rock’ in skating parlance, like a rocker of a rocking chair) not unlike the working edge of a skinning blade (e.g., Marble’s Woodcraft comes to mind). This blade is typically composed of a softer, more elastic steel (the bulk of the blade attached to the boot) and a harder steel (a small zone at the working, convex edge). The harder steel accepts and holds an edge, but the softer steel is necessary for flexibility as tremendous amounts of force are often applied to the blades (as in one of those big triple rotation jumps), and harder steel would break under such circumstances.
Now this 3/16” curved edge is given a shallow concave grind (across the thickness) along the entire length of the blade. Thus, if you sight down the length of the curved, convex edge, you will see a concavity (a slight trough) along the length from one end to the other. Since the sides of the blade are parallel to one another, the ‘U’ shaped concavity produces two edges with a shallow angle at the point where the tops of the trough and blade sides intersect. One edge is referred to as an outside edge and the other as an inside edge depending on which foot you referring. So, a skater will have two inside and two outside edges. Since the blade is curved along its length (some more than others depending on the type of skating), very little of the blade actually comes into contact with the ice. However, where the blade does contact the ice, that’s where the cutting edge of the skate blade does its work -- it cuts ice. I won’t get into the laws of physics here, in which friction governs motion, but basically depending on the blade’s angle of attack to the ice and the force applied to the blade edge, more or less cutting is accomplished to create movement in one direction or another. Since ice is slightly more forgiving than the hardened steel of the blade edges, controlled use of edge cutting creates speed and direction. Again, not unlike how one manages a skinning blade when dressing game. The better the edge, the less friction there is, making a controlled cut essentially effortless.
Now, about two edges on a blade, the inside and outside. Ideally, those two edges of a blade should be at the same height from the bottom of the ‘U’ shaped concavity. An uneven grind would require a skater to expend more effort by leaning further to get the lower edge to cut. ‘Evenness’ of height allows the skater to exercise far better control in cutting the ice with less effort, especially at extreme speeds (high or low). In fact, at the low end of the amateur scale (with which I’m familiar), there is a fellow who uses a machinist’s dial indicator to determine that the difference in height of the two edges doesn’t vary by more than 0.003 – 0.004”. He got disgusted with the run-of-the-mill grinding done at most ice rinks where his kids skated. With his knowledge of metal-working and machining, he built is own grinding bench and developed a system to achieve the fine tolerances that many have come to expect. In fact, individuals will drive several hundred miles with a car full of skates for him to sharpen.
Are they really sharp, you ask? Oh yeah…….I’ve seen skaters wipe the slush from skate blades with their bare hands. Not common, but the result is definitely not pretty. Anyway, expertly ground and honed blades in the hands (or I should say on the feet) of a competent skater who cuts the ice just so is a beautiful thing to experience; it is also testament to the person who spent the time to get those edges just right.
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