I was reading Verhoevens paper on sharpening and noted that he had trouble when the edge angle dropped below about 10-15 degrees. Now I know that not many people sharpen their knives that low, but I also know that Cliff sharpens in that range on large chopping knives apparently with out trouble. Verhoeven was using AEB-L stainless at 60 Rc for his tests. Also, many scandinavian style blades are ground at around 10 degrees per side, and my 1095 homemade kiridashi was about 20 degrees total and didnt seem to have trouble w/ taking an edge. Verhoevens work seems to be a popular reference, so I just wondered if anyone has experience with edges lower than those he had trouble with.
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Very Low Angle Edges
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Cliff Stamp
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Verhoeven noted that the edge formation was more irregular at the lower edge angles and the burr, which is what he called basically the extent of the non-perfect intersection, was larger. This is to be expected for a number of reasons such as carbide issues, the lower strength of a more acute edge, and the inherent more coarse finish produces at a given grit. What should be realized though is that this competes with the massive increase in cutting ability that such a reduced angle produces. That range of angles, 10-15, is indeed what I run on the non-cutting knives I use, meaning they are more for either utility work or very high stress cutting, like impacts or metals.
-Cliff
-Cliff
Cliff Stamp
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He notes that an included angle of 10-12 degrees will produce rapid degredation in kitchen use which I don't find surprising on a 60 HRC knife considering what kitchen use can entail. In general going that acute requires a higher hardness, 5-6 degrees per side is fairly acute and unless you are working with a high strength steel you would want to restrict the cutting to soft materials like rope/cardboard. The extended breakdown can also enhance long term slicing performance and again you have to consider the effect of the cutting ability on the lifetime and not just the edge retention as noted by Buck CATRA data.
Note that the difference in performance from the common 60 HRC knives to the actual optimal hardness of 65/67 HRC is actually the same as the difference between the 60 HRC knives and the "junk" mystery knives in the low fifties. So you would expect just as much a drastic difference in performance between the two groups. This is why when makers talk about 60 HRC being "good" enough or hardness not being so critical it should always be a point of contention because the same makers will have no issue with lambasting steels like 420J2 as being next to useless but they are just as much under maximal hardness as that blade is under theirs.
Back to angles, the angles Verhoeven lists in table 1 are grossly higher than required and he is just citing a reference which isn't actually based on wook but just repeats common misconception. 15-30 degrees per side is way too high for a chopping knife unless you are chopping metals. Felling axes for example are towards the far left of that range and the impacts they see are way above knives. For woods you can work with 13-15 per side even on hard woods and once you go above 15 the edge should be really robust and stand up to really abusive cutting like dead wood limbs. You need to adjust this for weaker steels but since strength/stiffness are quadratic/cubic in thickness you don't need to increase the angles much for extra stability.
-Cliff
Note that the difference in performance from the common 60 HRC knives to the actual optimal hardness of 65/67 HRC is actually the same as the difference between the 60 HRC knives and the "junk" mystery knives in the low fifties. So you would expect just as much a drastic difference in performance between the two groups. This is why when makers talk about 60 HRC being "good" enough or hardness not being so critical it should always be a point of contention because the same makers will have no issue with lambasting steels like 420J2 as being next to useless but they are just as much under maximal hardness as that blade is under theirs.
Back to angles, the angles Verhoeven lists in table 1 are grossly higher than required and he is just citing a reference which isn't actually based on wook but just repeats common misconception. 15-30 degrees per side is way too high for a chopping knife unless you are chopping metals. Felling axes for example are towards the far left of that range and the impacts they see are way above knives. For woods you can work with 13-15 per side even on hard woods and once you go above 15 the edge should be really robust and stand up to really abusive cutting like dead wood limbs. You need to adjust this for weaker steels but since strength/stiffness are quadratic/cubic in thickness you don't need to increase the angles much for extra stability.
-Cliff
Note that the difference in performance from the common 60 HRC knives to the actual optimal hardness of 65/67 HRC is actually the same as the difference between the 60 HRC knives and the "junk" mystery knives in the low fifties. Cliff
I kinda thought that might have something to do with it. What about the results he had from the 64 Rc knives he tested. I think one was 1080.
Cliff Stamp
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He found that 52100, AEB-L and 1086 all had similar edge finish, which would be expected as they are all similar in carbide size, < micron. The harder 1086 blade also had a finer finish, but he was seeing an effect of the honing machine limitation on the lower angles.
-Cliff
-Cliff
Cliff Stamp
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I have not used those machines, but grinding at that low an angle it doesn't seem unlikely to me to expect to see problems with high speed due to vibration and other similar issues. Since those angles are far lower than most run it is a non-issue in general which is likely why it doesn't come up.
-Cliff
-Cliff