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- Jun 26, 2009
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You guys are really arguing the same points from different sides. You may not realize it, but all of you are making convex grinds (even if you can make perfectly flat bevels).
Here's the explanation:
The entire reason knives have two (or more) bevel angles is to attempt to approximate a smooth profile curve with a (relatively) thick edge angle and thin blade geometry. This is the definition of convex. In essence all multi-bevel edges are convex edges. Even a hollow ground blade is overall convex from edge to spine (though with more complex geometry in the middle). The only difference is that V-grinds are approximations of convex curves using flat bevels. It's like approximating a circle with an octagon. A true "convex" grind simply does not approximate. It is the ideal smooth profile.
(Let's use a hypothetical blade that is 1" wide, with 1/8" thick spine. This will help visualize everything.)
The simplest edge grind is a full-flat from the spine to the edge. This grind is accomplished with a single V-shaped bevel. It is the ideal V-grind. We don't make knives like this, though. The edge angle is too thin for anything but a straight razor (about 8-degrees inclusive for our blade). It would also be slow to sharpen because you have to remove a great deal of metal each time.
So we must compromise by adding another bevel angle. This can be accomplished two ways, either not grinding all the way to the spine (scandi grind), or by making a secondary bevel. This way we can keep our thin spine thickness while increasing edge angle to something that will hold up under use. These two angles approximate a curve made up of two control points.
Many advanced sharpeners will improve their blade performance by adding more V-bevels, such as micro edge-bevels and lower-angle back bevels. This allows the user to tailor the performance of the blade to its intended task by adding more control points to the curve.
This is where the argument starts taking place:
Many of you are comparing a simple convex edge (few control points) to a complex v-grind (many control points), or vice versa. A convex edge made on a soft backing is akin to a simple v-grind or scandi grind. Both curves can be defined with two angles. One as a spline-curve and the other by two flat planes. The result is simple (but not likely optimized) edge geometry. More complex "convex" or v-grind geometry can fine-tune the durability and thickness properties of the edge for a given cutting-task. It helps to make either of these geometries on flat stones for maximum control.
The real question is whether there's a performance difference between flat-sided approximations or smooth curves. I honestly don't know. It would be difficult to define or test. You would need to make identical blades with identical bevel-geometries. Then there's the issue of where to define the control points that define the ideal curve. There are several algorithms, that, while all being correct, would yield different results.
Phillip
Here's the explanation:
The entire reason knives have two (or more) bevel angles is to attempt to approximate a smooth profile curve with a (relatively) thick edge angle and thin blade geometry. This is the definition of convex. In essence all multi-bevel edges are convex edges. Even a hollow ground blade is overall convex from edge to spine (though with more complex geometry in the middle). The only difference is that V-grinds are approximations of convex curves using flat bevels. It's like approximating a circle with an octagon. A true "convex" grind simply does not approximate. It is the ideal smooth profile.
(Let's use a hypothetical blade that is 1" wide, with 1/8" thick spine. This will help visualize everything.)
The simplest edge grind is a full-flat from the spine to the edge. This grind is accomplished with a single V-shaped bevel. It is the ideal V-grind. We don't make knives like this, though. The edge angle is too thin for anything but a straight razor (about 8-degrees inclusive for our blade). It would also be slow to sharpen because you have to remove a great deal of metal each time.
So we must compromise by adding another bevel angle. This can be accomplished two ways, either not grinding all the way to the spine (scandi grind), or by making a secondary bevel. This way we can keep our thin spine thickness while increasing edge angle to something that will hold up under use. These two angles approximate a curve made up of two control points.
Many advanced sharpeners will improve their blade performance by adding more V-bevels, such as micro edge-bevels and lower-angle back bevels. This allows the user to tailor the performance of the blade to its intended task by adding more control points to the curve.
This is where the argument starts taking place:
Many of you are comparing a simple convex edge (few control points) to a complex v-grind (many control points), or vice versa. A convex edge made on a soft backing is akin to a simple v-grind or scandi grind. Both curves can be defined with two angles. One as a spline-curve and the other by two flat planes. The result is simple (but not likely optimized) edge geometry. More complex "convex" or v-grind geometry can fine-tune the durability and thickness properties of the edge for a given cutting-task. It helps to make either of these geometries on flat stones for maximum control.
The real question is whether there's a performance difference between flat-sided approximations or smooth curves. I honestly don't know. It would be difficult to define or test. You would need to make identical blades with identical bevel-geometries. Then there's the issue of where to define the control points that define the ideal curve. There are several algorithms, that, while all being correct, would yield different results.
Phillip
