What is “Sharp”
- This topic has 48 replies, 12 voices, and was last updated 04/06/2014 at 2:40 pm by
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Another epic thread, my friends! B) Thanks for the heads up, Eamon!
The answer, as we are seeing, is “it depends” – as usual. However, I think the combined data here is answering our specific question of “what is sharp” but not all at the same time.
First, the textbook definition, which is when two planes meet at a point of zero width (or close to it for all you OCD’ers like me, since zero is theoretically impossible). This is usually measured by the raising of a burr on both sides of the blade and is “sharp” by definition regardless of the grit. As Eamon basically stated, an 800 grit edge is great for cardboard but not something you would want to shave with, but both are technically “sharp”.
Then there is the geometry to take into account – more acute angles will slice better and easier, but more obtuse angles will withstand a pounding longer. tcmeyer noted how a relatively unrefined the scalpel blades are, yet they are very thin and slice with amazing ease. Your axe needs more geometry and heft behind the blade to withstand the chopping forces.
On the less tangible side are the steel characteristics, which influence your overall refinement and geometry choices. As Clay mentioned, “There is a physical limit as to how thin an edge can be with steel”. As we approach that zero width, more obtuse geometry will help support the edge so that it can stay intact. (This is the reason for convex edges and micro bevels).
That’s the easy part. Now is the stuff that makes you stay up at night… 👿
The thinness or thickness of the edge is important,too. Diamonds plates cut through the edge very deeply, scoring the blade so that the voids from the scratches end up making the serrated teeth of an otherwise “thick” edge. The best (slightly exaggerated) image I can think of is the teeth of a backhoe, where the diamond scratches equate to the spaces between the teeth.
This is what allows for what I call a “false positive” when shaving hair off of lower grit diamond plates. The gaps between the teeth are sharp and cleanly cut, which catches the hair between the points of the VVV. Keep in mind that the points themselves are still quite thick. This is sharp, though.
When you get into the way that the ceramics and water stones abrade, they tend to abrade the entire surface of the edge more evenly, thinning out the thickness of the edge until the points of the V are thin enough to sever hair – which gets easier at about 2K and finer – more of a — shape.
Here are two pictures where you can see the thickness of the edge of the edge. The first is the 600 WEPS Diamond – it is uniform, but the scratches are quite deep. The second is the 600 Chosera. You can see the more rounded edge of the edge, but the scratches on the bevel are much less invasive.
The diamond edge in this case is “stronger” but it is sawing more than slicing.
The argument here becomes having an edge that is thin enough to sever cleanly through the fibers of what is being cut, rather than sawing or even tearing through. The tradeoff is that the more refinement you add, the closer to that zero width the edge becomes, hence the need for more geometry. Even with diamonds.
Then we have polished grooves to consider. tcmeyer’s razor blades have a thicker edge of the edge because of lower refinement, but the grooves are polished clean, giving the relatively thicker points of the VVV just a slightly thinner or convexed profile so it can cut into things a little easier. Most factory edges are about 220 grit with a polish that allows them to slice easily through paper, yet be rugged and longer lasting – they may shave arm hair but are nowhere near what I would call shave ready.
On the opposite end is the “true grit”, which is the full established scratches of the finest grit, making the edge cut effortlessly, like a straight razor, but is more fragile and requires more upkeep to keep it in optimal condition.
Which is better? Well, that depends. :silly:
Back to the tomato cutting issue. The 800 edge saws, the 10K edge slices as Josh mentioned. If the 10K edge isn’t working as well it’s probably because the edge has been rounded from too much pressure in the finishing stages, as Leo suggested, or the geometry is too acute for the steel.
One thing that always gets me about some of the chef knife users out there is that they feel the need for “lasers” which are super thin blades with super thin angles – like 12 degrees per side. However, with something as precise as the WEPS combined with the Choseras and Shaptons, approaching that zero width is easily done, and actually requires a more obtuse angle or a microbevel – either way, about 18-25 degree angles per side to hold up for more than a couple of slices (IMO).
In reading this post over, I fear I may have only made the question even more difficult to answer!
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