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- Mar 8, 2008
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There are a number of factors of tool/task suitability and performance that I've teased out over the years that I rarely see delved into in detail, with edge presentation and engagement being one of the larger ones so I figured I'd put some of my thoughts on the subject out there.
To begin with, let's get some definitions out of the way. First is what I call the "cutting line" or the line that describes the edge. A very simple concept, but this is important because of how it interacts with the next two terms.
Edge presentation is how the cutting line is oriented relative to the line of the stroke being performed. This interacts with the final term.
Edge engagement is how much sliding force vs. pushing force is occurring during the cut. For instance, a chisel almost entirely with pushing force while a deli slicer is cutting with mostly sliding force (although all slicing cuts require SOME pushing force in order for the edge to touch the target.)
These three things combine with ergonomics to help inform you of what the tool is best at doing. Because those factors are put together in a way that is supposed to interface with the natural and comfortable movements of the human body, examining the shape and placement of the cutting line when held in various grips and how that affects the edge presentation during various strokes to produce varying degrees of edge engagement will often reveal the various ways to apply the tool in a useful manner to a wide array of tasks.
However, this is easily one of the most glossed-over areas of design assessment except in very vague surface-level terms like "I like a knife with a belly" or "I like a knife to be straight at the base of the blade" without exploring why that preference exists and what that edge presentation does to engagement in various tasks and makes it more or less suitable to certain applications. Much like a "this grind vs. that grind" debate, where the grind is merely a symptom of the underlying factors of stock thickness, blade profile, and grind angles, so too do edge engagement and presentation get overlooked in discussion of one tool vs. another for certain uses and environments.
To begin with, let's get some definitions out of the way. First is what I call the "cutting line" or the line that describes the edge. A very simple concept, but this is important because of how it interacts with the next two terms.
Edge presentation is how the cutting line is oriented relative to the line of the stroke being performed. This interacts with the final term.
Edge engagement is how much sliding force vs. pushing force is occurring during the cut. For instance, a chisel almost entirely with pushing force while a deli slicer is cutting with mostly sliding force (although all slicing cuts require SOME pushing force in order for the edge to touch the target.)
These three things combine with ergonomics to help inform you of what the tool is best at doing. Because those factors are put together in a way that is supposed to interface with the natural and comfortable movements of the human body, examining the shape and placement of the cutting line when held in various grips and how that affects the edge presentation during various strokes to produce varying degrees of edge engagement will often reveal the various ways to apply the tool in a useful manner to a wide array of tasks.
However, this is easily one of the most glossed-over areas of design assessment except in very vague surface-level terms like "I like a knife with a belly" or "I like a knife to be straight at the base of the blade" without exploring why that preference exists and what that edge presentation does to engagement in various tasks and makes it more or less suitable to certain applications. Much like a "this grind vs. that grind" debate, where the grind is merely a symptom of the underlying factors of stock thickness, blade profile, and grind angles, so too do edge engagement and presentation get overlooked in discussion of one tool vs. another for certain uses and environments.