Yes, that is the issue, it basically looks flat. It is changing but the changes are tiny compared to the scale due to the non-linear relationship. What happens is a little complicated but not overly so, there ends up being competing factors between what is blunting the edge and what is sharpening it, and as you get very dull the latter can actually start to be larger than the former. If this makes no sense, and it might not initially, then just think about the following.Fancier wrote:I have a really hard time seeing any trend at all after the 150m point in that graph.
When the edge blunts it is basically just getting thicker. It starts off at about 0.5 micron and because it is so narrow it generates very high contact pressures and it cuts with very low force - i.e., it is sharp. As the apex thickens due to loss of material, fracture, and deformation then it starts requiring more force to generate the rupture pressure (what is needed to cut the material) and thus it is dulling (more force needed to cut).
But the edge is not going to wear smooth, it also gets "rougher" as it dulls as pieces are tore out of it for various reasons. If you look at the edge under magnification (say 50X linear) you can see a piece of apex go smooth and then get rough. This roughness generates a very low kind of sharpness. It is no where near optimal sharpness, but it will keep a knife cutting at a low level of sharpness.
If you know a little about the mechanics you can even abuse this during the cutting, or maybe manipulate it would be the better term. For example there are generally two types of cardboard.
-soft and abrasive
-hard and not-abrasive
The first type doesn't tend to make edges chip much, the second does (because it requires higher rupture pressures). Thus you can often "sharpen" a knife by cutting through a piece of the hard cardboard in the middle of the run. If you cut through a lot of the second type you can cut for a very long time and nothing tends to happen at all because the abrasion is low (so the edge isn't thickening) and the fractures are high (so the edge is chipping).
I did some very low sharpness edge retention runs early on and did ~2000 slices on ropes for example with D2 blades and similar and concluded that if I was going to cut clean material with knives then then volumes to make a knife not cut paper are tremendous because of that non-linear effect. Chris (who posts here on occasion), has tried even with very simple steels and again can produce large volumes. If you want to see really huge piles look at what Boye used to do. Boye's steels had huge aggregated carbide networks as they were cast steels and if you sharpened to low levels they would basically self-sharpen at some point faster than the apex would thicken by wear. The issue I had with them was simply outside of stock work, what are the odds you actually make 1000 cuts through clean rope and never hit an inclusion and it only takes one hard contact to remove the sharpness completely. Still though, he made some fine cutting blades in his original drop point hunters.