Best BESS score by edge angle

[wootz]

This is for people who use our software Grinding Angle Setter for Tormek and also have the BESS sharpness tester.

You must have noticed that a 20 dps and 15 dps edge never scores on the sharpness tester as well as the 12 dps, let alone 10 dps edge, despite showing the same keenness in the hanging hair test.
Many a man on this forum put true razor edge on the knives, so can you confirm my observations that the razor sharp edge will score:

10 dps edge near 50 BESS;
12 dps edge 50-70 BESS;
15 dps edge 70-90 BESS; and
20 dps edge near 110-150 BESS.

I am looking for confirmation from others of this "best score by edge angle" pattern.

[John_B]

Is it possible that the difference in force needed to cut the test medium is due to the extra force needed for the wedge to penetrate the medium? It would be interesting to look under a microscope at the test medium that the blade has just contacted but not cut through. Better yet would be a using a very high speed camera to see what is happening.

[Sharpco]

Actual angle was 17.5 degrees.(Target angle was 16 dps.)

Sharpening & honing with Tormek(FVB & Software) and finishing with Jende kangaroo leather strop & Jende diamond emulsion 0.25micron.

Tester was PT50A.

[Ken S]

Wootz,

The logic of your post is or should be self evident. I would not expect a cleaver to cut as easily as a paring knife or a cold chisel to cut as easily as a thin paring chisel. On the other hand, neither of these delicate tools will survive long against bone or metal.

The tool and edge angle must match the work.

Ken

[John_B]

I think the dilemma we have is that as good as it is the BESS device measures cutting force for a push cut. SHARPCO has a good video on how to apply a measured force to reduce this variable. We use this push cut force score to correlate it to sharpness. Sharpness is actually how perfectly the edge apex is formed. As we see in the many SEM photographs the apex is not as perfect as imagined. Much of Wootz's excellent work centers around achieving as near perfect an apex angle as possible.

An ax can be sharpened to a razors edge even though the cutting force is greater on a push cut due to the higher angle and more material behind the apex. We also see this when comparing an old European knife to a Japanese knife of the same era. The European knives were typically sharpened between 20° and 25° DPS while Japanese knives were mostly single edges at 15°. Both knives could be sharpened to a razor sharpness, however, the Japanese knife appeared sharper as much less force was needed to make a slice with the thinner blade. As the blades we sharpen get closer and closer to having the perfect apex I think the limits of the BESS measurement method may be reached. I see no reason why identical 12° DPS and 20° DPS knifes apexes cannot be equally as sharp.