High Polish Edge, 30°
Obviously, the angle is the included angle. As usual, I always try to lower the edge angle to its limits for the knives I use purely for cutting. If I expect any chopping or harsh materials then I keep steeper angle, but otherwise, why not make it more acute, cuts much better. With CPM 10V steel I had another interest, how would it behave with polished edge. I've exchanged few emails with Phil, and eventually figured out to put 15° per side edge, which gives 30° included as indicated above. Actually, 15° per side angle can be considered general lower limit for high carbide volume alloys like CPM 10V, CPM S125V, CPM S110V, K294, K390 and many others.Sharpening - Even though I own a large array of various sharpening stones, rods, devices and whatever else I have never had so much trouble with rebeveling a single knife except for the ceramic blades, although CPM S125V is worse :) CPM 10V steel simply doesn't want to give out its atoms to the abrasives. The original edge wasn't much higher than 15° I was attempting to achieve. To some degree difficulties were expected, rebeveling implies removing fairly large amount of metal, and it is never easy with high wear resistance steels, edge restorations on the other hand are very quick. In other words, the larger the surface area you are grinding, the more difficult things are.
It still took over 3 hours using edge pro and DMT stones to get down to 15° edge with 800 grit. After that I took a break and spent another hour or so polishing the edge, which went much faster and I've proceeded with 5µm, 2µm abrasive films followed by Kitayama Japanese whetstone(1µm ) and then stropping on the leather loaded with CrO - 0.5µm, then 0.3µm abrasive Al2O3 film. Finally stropping on the plain leather and I was done! The result was satisfying though. The edge was extremely sharp, and hair whittling was effortless. In retrospect, had I chosen a coarse benchstone e.g. DMT Dia-Sharp D8XX or Shapton™ 220Grit Glass Stone things would've proceeded faster. Even though Edge Pro is a fast and efficient sharpening system, stones are narrow compared to benchstones and there is no way around that.
CPM 10V carbide grain size is around 2µm-4µm, which is much smaller than D2 - 10µm and 154CM - 40µm. Never heard anyone advising against using finer abrasive on later two, never had problems with them either. So, that's why I've decided to use abrasives all the way up to 0.3µm.
Now, there is always a debate in knifaholic's world, whether or not it is worth or not to sharpen the edge with the abrasives finer than the grain size of the alloy. The argument against it being that large carbide grains sticking out from the softer metal matrix are breaking out. I was not entirely convinced by that theory. For one I didn't see why the same carbides wouldn't break out with bigger grits, after all it's still abrasive action. Second, particles can be broken, not entirely removed, thus creating new cutting surfaces. In the end, that was proven to be wrong, and the reason is that once you get to very thin, refined edges which happens with finer abrasives, steel matrix is too thin to hold larger grains in place and that's all to it. Still, mistakes are part of learning :) That doesn't exactly answer the question about using finer abrasives than carbide size, but does answer the question about very thin edges on high carbide volume steels.
In the end, steels with high carbide volumes do not perform well with the edges lower than approximately 15° per side. Some alloys, such as ZDP-189, SRS-15, SKD11 can go lower, ~12° per side, but below that microchipping becomes an issue. I have my Akifusa(Ikeda) gyuto at 12°, no problems whatsoever, and I used it pretty much daily, before it was retired with being replaced longer, 270mm gyutos.
Cutting Performance -
First test was again cardboard. However, expecting rather fast sharpness degradation I didn't cut a lot of it. Around 100" just to get the feel of push cutting through it. Second, I didn't have much of it to begin with. IN the beginning, push cutting was much easier, due to high polished, refined edge. As for the slicing performance. Well, honestly I didn't notice any decrease with slicing motion initially. Obviously that was due to the very sharp edge. The pressure generated by much thinner edge, is greater compared to coarse edge that any advantage coarser edge might have with its teeth is simply negated. I've tried three different types of rope, manila, nylon and something else, synthetic, etc. Anyway, the result was that polished, extremely sharp edge still sliced better than the coarse one, initially and that's the key point.One thing that was obvious and expected, was increased rate of the edge degradation compared to the original coarse edge. Although, to commend the CPM 10V steel I have to say it could still do hair splitting trick even after 100" of cardboard, which is pretty harsh abrasive. After that I've proceeded with cardboard, again and testing the rope cutting with slicing motion after every 200 or so inches of cardboard. Eventually, my tests were aborted due to lack of test medium. All the cardboard I had was reduced to less than 1" squares and I didn't want to torture myself with it.
Later that day and following 4 weeks I just continued to use this knife w/o sharpening. The only maintenance it received was steeling. Although I'm a very big proponent of steeling with a smooth steel, I was rather suspicious of its benefits on the knives with Rockwell hardness of 64 or higher, simply because, the steeling rod itself was hardened to 63HRC. Basically, the steeling rod is "softer" than the knife. Perhaps smooth ceramic is a better choice in this case, or a borosilicate rod, if you manage to find one. Anyway, few days later, I've noticed that slicing performance now was worse than the initial rough edge. Bear in mind I'm a software engineer, not a pro chef or a trapper, thus I didn't use it few hours a day, just whatever cutting I've happened to do, and I wasn't using slicing motions at all times either. It took some time till the edge degraded so much that I took notice of the degradation.
In retrospect, I can tell why it took long time to notice the edge degradation. Phil Wilson knives are exceptionally high performance cutters, and significant part of that very high cutting performance is the thin blade, with very small behind the edge thickness. Combine that with high strength steel, and even with relatively dull edge the knife can still outcut majority of the factory knives, because blades are thicker and behind the edge thickness is several times of that's on Phil's knives. That made push cutting tests on cardboard rather meaningless, the knife would cut for a very long time, edge degradation wasn't abrupt, and even though the aggressive bite of the edge was gone, thin piece of high hardness metal would still separate cardboard. On one hand, cutting was still pretty easy, but when determining coarse vs. polished edge, then forces for each type of the edge should be compared using appropriate cutting type. I.e. slicing for coarse edges and push cutting for polished edges.
Unfortunately I didn't use any force gauge initially, probably I should've done it. I'd detect changes a lot sooner, as the human hand and senses are not exactly the high precision instruments. At least no at the levels required for this sort of testing.