Jeff Clark :
[thin, sticky, elastic material]
For these materials the ideal would be a knife that was simply the edge with nothing behind it
Yes, this is why the idea cheese cutter is simply a piece of wire, or even string. For knives, hollow grinds are a solution, but I prefer hollow relief and not traditional hollow as the latter bunches up badly and only works really well on a very small class of materials. I wish hollow relief was more common as its only drawback to flat is a lack of durability and that is no an issue on just pure cutting knives.
Chad :
[edge angles and edge retention]
In regards to edge retention, one of the things which really confuse the issue, is that people refer to edge retention as basically the lifetime of the cutting ability, when in fact it is the lifetime of the sharpness of the edge. Sharpness influences cutting ability, but is only one of many factors. Making them equal leads to really skewed conclusions. For example if you take a knife that has an obtuse edge grind and compare it to a knife with a very acute edge grind, the more obtuse one will cut worse - this is no surprise. This also means that given the same amount of edge degredation, the finer edge will outperform the more obtuse one. Thus the finer edged blade needs to suffer a much larger amount of edge degredation before its cutting ability is reduced to the ability of the thick edge blade. People often refer to this as "greater edge retention" and draw skewed opinions of steels because they attribute this difference to the materials involved when in fact it is the geometry.
For example, when I got the SOG SEAL 2000 I did the standard rope cutting tests for edge retention and found that the knife dropped down in cutting ability to below standard levels that I use (force to cut thread, length of edge to cut light poly, force to puch cut 3/8" hemp), in about ~14 cuts. The Twistmaster from Cold Steel, takes ~126 cuts to get to the same level of cutting ability. Most people would tend to write off the performance of the SOG as just being to a softer, lower class stainless steel as compared to a decent carbon tool steel. However after looking at this class of performance very carefully in the last few months I have come to the conclusion that this really isn't the case and the difference in geometry is the main effect. The influence of the geometry can be eliminated and thus produce an estimate of the edge retention, but its not trivial to do so. When this difference is eliminated, I have been surprised to note that the difference in edge holding (independent of geometry) is very small over a wide range of steels and in particular to hemp rope, is mainly dependent on RC hardness, and that the alloy makes only a minor effect.
Decreasing the angle is generally promoted as lowering the "edge retention", however I have found that as long as the edge is not reduced to the point where it breaks apart during the cutting, the lower the edge angle the greater the lifetime of the cutting ability simply because the cutting ability has been increased. In general you would expect that the edge would roll easier, but you use less force when you have a more acute angle because the cutting abliity is greater. However for a general "utility" knife, I would put a more obtuse secondary edge on the puukkos because they would get damaged on rough work, these really isn't knife class chores though. One of the things I have been meaning to look at is does the application of a small secondary edge bevel (~0.1 mm wide), effect edge retention as it has little to no effect on cutting ability thus it is far easier to make a direct comparison.
I have never heard of anyone using an oil quench on an air harding steel
Oil quenches are a standard option on many steels commonly air hardened, some makers are familiar with this and some are not. There was a dispute on Bladeforums awhile ago on water quenching 5160, it was put down by a number of well respected makers as a horrible mistake, yet it is used on the HI khukuris which are a very high standard for extreme use knives (it is common in many places where they can't afford oil). In general oil induces a greater hardenability. For example oil quenched M2 is 2-3 points harder than air quenched M2 when tempered above 1000F even though after quenching they are both at full hardness ~66 RC.
I am a little concerened that you were making an argument against "custom" heat treaters when you did not even know what type of heat treatmentis involved, it kind of reminds me of your assertion that the Busse folder is the best even though it has never been seen outside the Busse shop.
In regards to comments on the "inferior" nature of production heat treat, my statement was one of skepticism. If you want to make the arguement that your methods are better than production then you should be backing that up with actual data, either yours or someone elses, not just vague comments without even an estimate of the order of magnitude of the effects involved. It is the people making the claim that have the burden of proof, not the other way around.
In regards to the comments I made about the Busse folder, I have discussed folder specifics with Busse, referencing the problems I have had with many current mechanisms, before he even mentioned they were making a folder in fact. Based on these conversations, his attitude towards performance in general, and my experience with his knives, I would be willing to bet heavily on a folder coming out from Busse Combat in regards to durability and overall functionality. It is that simple.
Is it possible that Busse would come out with a lousy folder - yes. But I don't think it likely, not even a little considering the whole promotion of the knives is performance based. And if this does indeed turn out to be the case, then I will be one of the first ones to critize the knife.
[opinel folder]
With the edge angle taken as low as you have taken it, have you seen any drastic decreases in durability?
I would not cut hardened metal or bone with it, but anything else would be fine. In general modern cutlery edges are far too thick, a generation ago they were all ~1/3 of what is common now. This makes no sense as we should be building better knives, not worse ones. As an example of what it takes to damage such an edge, I recently reprofiled the edge on a MPK-Ti down to 9-11 degrees per side. After several hundred chops through wood including scrap lumber and several year seasoned felled wood, the edge showed no visible damage. I then split a dozen small knotty rounds using a 1.5' piece of fir as a mallet. I was using enough force to on occasion cause the wood to shatter and the mallet would also be destroyed periodically in the process. The edge was again undamaged. I only managed to put a small ripple in it when I went to split one last piece and it broke in the middle and I ended up hitting the knife in such a way to induce a lot of lateral strain across the edge. This induced a small ripple about ~1mm long and half as deep. It was easily steeled out.
What level of edge polish are you using? Any convexity added to the edge bevel? Do you find the steel fine enough grained to be able to use both very high levels of polish and very thin edges with out seeing tearouts?
For the general edge testing work I run it with a 22 degree microbevel (0.1mm wide) for no other reason than I have a v-system that is preset to that angle and it fits a ceramic, diamond and steel rod. When I am not doing this I leave it as finished on sandpaper. That edge bevel I would assume has a small bit of convex curvature induced because the leather compresses, from other blades with larger bevels I would assume this is only ~1 degree of so of additonal angle. For the edge I usually run it stropped at CrO for most work. I do experiment with more coarse finishes, when just means leaving it at 5 micron SiC. These work a lot better for rope and such, but even at a high polish, the blade will put cut through even 3/8" hemp with only ~10-15 lbs (don't have the numbers on me right now), so it can simply push cut most materials well enough that slicing is not really needed. In regards to the steel, from what I have read it is just ~1075, no large alloy carbides to break up the edge. I have checked the edge under magnification (20x) at a high polish and it is smooth, unlike for example ATS-34 which breaks apart at that angle.
-Cliff
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