I haven't seen where Jim sharpens to that fine a finish for his rope slicing testing. I thought he used the 300-400 grit mold master stones from Congress Tools on the Edgepro for his test edges. I haven't read all this thread, so maybe I missed it. I don't think edge stability has a relation to sharpening to a finer edge. It's just that the steels with higher edge stability also happen to be easier to sharpen. Verhoeven didn't do his experiments on high carbide steels. That waviness he describes might well have been edge crumbling, even at the angles he used. The way Jim sharpens, I wouldn't expect a difference between the different steels in initial sharpness. Were there to be one, it could also skew the results. It can certainly do so in CATRA testing.
I think it's a misconception that edge stability is a replacement for, or somehow opposes, wear resistance. No one argues that high wear steels wear slower than low wear ones. What is in contention is cutting ability, which higher stability steels can have over high carbide/wear ones. The high wear steel edges are not stable at lower angles, thus they have lower cutting ability, not lower edge holding/wear, unless one takes advantage of the edge crumbling on abrasive, but relatively soft, materials. Some people prefer different attributes, and some applications demand them. Also in contention is the ability to hold a high sharpness edge. Since a lot if the initial sharpness loss is due to rolling and deformation of the edge, the higher stability steels have an advantage here, or at least no disadvantage at thinner geometry. IMO, few people sharpen to a low enough angle or demand so much of their knives that they'll notice the advantages a high edge stability steel can offer.
Testing protocol is at the top of the first page:
Cutting 5/8" Manila rope on a Scale with wood to cut on. The scale was calibrated for the weight of the wood. Making 3 to 4 slicing cuts from back to tip using the least amount of down force needed to get the starting down force. Once that was established 20 cuts were made then down force was tested again and that continued until 20 LBS was reached.
All the knives started at 14 ~ 15 LBS of down force except for M390 because it cuts so aggressively.
Accuracy is to + or - 10 Cuts and + or - 1 LB of down force or 6%. This was verified doing a blind test of blades of unknown hardness until they were tested after. 2 blades of the same hardness and steel, sharpened the same and same model of knife.
RC hardness is + or - 1 RC on the steels that were tested as the standard of RC testing.
All edges were at 30 degrees inclusive and polished to 6000 grit on the Edge Pro, sharpness was tested by slicing TP clean.
Note that all knives were polished to 6000 grit Edge Pro at 15-dps and tested on TP. While he does not measure apex diameter on SEM as above, SEMs of blades sharpened in similar fashion produced 0.2 um edges. It is reasonable to assume that Jim's edges are of similar thickness at the outset, and all knives should have the same level of sharpness. Note the acquisition of "starting downward force" involves making "3 to 4 slicing cuts from back to tip", i.e. the knives are used to cut the medium to acquire the
first measurement... and all measure ~ the same. This tells us that
at this geometry, on this cutting medium, there is no detectable difference in edge stability within those first few cuts, i.e. the edges of the high-wear steels did not crumble away or show any less stability than the low-wear steels at such a low thickness with a 15-dps edge angle.
Cutting stops when 20-lbs is reached, at which point all knives should again have the same apex diameter. I'd love to know what that thickness is. I'd also love to know how high up the bevel the dulling damage extends, as that would provide information on the performance of alternative edge angles. The edges of the low-carbide edge-stable blades deteriorate more quickly than the edges of the high-carbide less edge-stable blades. If the low-carbide blades held a sharper (thinner) edge longer than the high-carbide blades (as their supposedly higher stability would suggest), that advantage was lost
within the 5-lbs increase in applied cutting force. It would be neat to know where that transition occurred or if it was too early to detect by measuring every 20 cuts.
Now, it could be that that the edges of all knives do NOT have the same apex diameter when 20-lbs is reached, that the edges deteriorated
in different ways that advantage the high-carbide steels in this test. For example, the low-carbide blades deteriorated by edge-roll which thickens the apex and thereby reduces cutting ability MUCH faster than edge-chipping. It could also be that the low-carbide edges smoothed down while the high-carbide edges chipped into micro-serrations which, again, feature higher cutting ability. In either case, the high-carbide steels have
higher cutting ability, not lower. Would this be any different at, for example, 10-dps where Verhoeven describes apex
instability (but to a very shallow depth) in low-carbide steels? Perhaps the instability would reach higher up the blade on a high-carbide steel?
Would this be different carving/chopping wood (non abrasive)? Well, neither of those applications requires a very thin (e.g. 0.2 um) apex diameter, so shallow instability is irrelevant. If the low-carbide steel folds over while the high-carbide steel chips away, unless the chipping is
much deeper (i.e. to greater edge thickness), the chipping steel still stays sharper (thinner) longer, but you may never notice if both are "stable" (neither folding nor chipping) at a thickness low enough for the application, e.g. 5 um? If you thin the edge via angle reduction to 10-dps or lower, at what thickness do you lose the strength required for the application? Is it really all that different, performance-wise, between low-carbide and high-carbide steels? If your CPM-M4 blade was NOT compromised by a "burnt" edge, then the difference is truly profound! But I would be surprised.
For cutting very soft non-abrasive materials, e.g. surgery, all that is required is a very fine, thin edge - it doesn't need to be very strong. Both low & high carbide steels can achieve that, but perhaps low-carbide steels will resist rolling noticeably longer than high-carbide steels will resist chipping at the edge of my scalpel or point of my needle? I doubt the advantage of the low-carbide steel.
For cutting very hard or dirty materials, the edge needs to be strong and tough but will still lose its very fine edge quite quickly via denting/rolling or chipping regardless of carbide volume? Again, I doubt the advantage of the low-carbide steel.
I think you are right that few people sharpen their edges to such low angles, but I think the reason is because the cutting advantage offered isn't as high as some purport it to be when weighed against other durability issues. Again, the studies of low-carbide
razor blades demanded angles of ~15-dps to maintain durability.
Cutting ability is enhanced NOT by sharpening to a lower apex angle that reduces durability but by thinning the blade
behind the narrow edge-bevel, i.e. a thinner
primary grind or a back-bevel.
As to the advantages offered by low-carbide steels, I see two which my supersede all others: 1) price to manufacture, 2) ease of both initial grinding and subsequent edge maintenance. If the steel is 10x less and performs as needed for a given application, why pay more if you do not need it? And if the edge blunts/rolls but can be re-aligned or resharpened to the needed level for the application more easily, :thumbup:
