In fact the use of CATRA data on a knife is itself biased if the results are going to be used to infer human performance. This again will have people like Thomas ranting but there are trivial example that show this to be true which are just based in math. There are knives made out of materials which can run on a CATRA testor for a day (yes, full day) and show NO DEGREDATION.
To be clear, the knives show no loss of edge at all. Now would that mean you would immediately jump and start screaming how you found the ultimate blade material. Yes, if you were a machine then you would be really excited but you are not and there is a huge difference in how a person uses a knife and a machine and the CATRA machine ignores this and thus the data set is baised by defintion if you make that inference.
Very interesting, informative and entertaining debate... I have to agree with Cliff that the ultimate test is what happens when a person uses a knife.
Please let me clear up a misconception, which I tried to address earlier. Apparently it didn't take.
The test we have performed is
not a CATRA Edge Retention Test. This was a deliberate choice on our part. The CATRA ERT uses cutting performance in a very stiff medium to measure sharpness, and uses a medium with embedded abrasive (silica) to wear the blade. As Cliff noted earlier, the hardness of an abrasive medium is very significant when looking at sharpening knives of different metallurgy, because the hardness of the abrasive relative to the hardness of the carbides in the blade is very important.
As an example of this, please look at the the following photos:
This is a scanning electron microscope image of a Talonite blade sharpened according to our test sharpening procedure. Notice that the final microbevel is approximately 20 microns wide (20 microns is about 0.0005 inches). You can see the presence of the carbides in the alloy, because they're slightly raised compared to the matrix. But the carbides have been ground to the edge geometry, and this blade is shaving sharp.
This is an SEM image of a Talonite blade after a CATRA ERT test. Note that the original sharp edge geometry is gone, and that the edge is rounded and has protruding carbides. This edge won't shave, and when handled feels dull. But because the carbides protrude from the edge, the blade continues to cut the CATRA media Results like this convinced us that the CATRA ERT test is not a good test for observing how long a knife stays sharp when used in cutting the kind of less-rigid materials that are usually used with hunting knives.
Therefore, we developed our own edge retention test
We wanted a test that would measure sharpness by measuring the amount of force required to cut into a flexible medium. Fortunately for us, CATRA makes just such a piece of test equipment, the Razor Edge Sharpness Tester
(CATRA REST Tester). This test performs a push cut on a flexible silicone medium and measures the maximum force required to initiate a cut. I believe it's a significantly better measure of sharpness than the cutting ability in the CATRA ERT, but you can feel free to disagree. Nevertheless, it's what we chose.
We also wanted to use a typical biological material to wear the blade. Rather than using sand-impregnated paper (which is the CATRA ERT test media), we chose to use hemp rope. The hemp rope should be softer than all of the materials in the edge region of the knife, and thus the effects of variable hardness in the edge should be minimized. We wanted to be fair, and to see how the sharp edge geometry fared in wear tests.
Therefore, we made a machine that is similar to a CATRA ERT machine, but uses 1" hemp, rather than CATRA wear media.
There are two possible metrics for how much wear was occurring on the blade: the number of strokes and the total media cut. Therefore, we measured both.
The test procedure is straightforward. We measure the REST sharpness, then cut the rope for 20 or 40 strokes, then measure the REST sharpness again.
There are at least two significant differences in the results of this test compared to the CATRA ERT test. First, we don't have sharpness data for every stroke. We only have sharpness data when we stop cutting rope and go measure the sharpness. We've done this, because we want to measure the user experience, not the machine experience.
Second, the media is significantly less abrasive than the CATRA media, so that wear occurs much more slowly. We stop the test when the blade stops shaving, which is still in the "early blunting" region of the ERT test that Cliff refers to. We do this on purpose. We want to see when the knife stops being sharp, not when it's so dull you can't stand it anymore. We tried to model the effect on a user who wants to keep his knife so sharp it'll pop hair off your arm.
Because this is a different test than the CATRA ERT test, there is no reason for ERT analysis methods to be applied. That's why we didn't do it the same way Clilff has done it. But we're happy to make data available for others to analyze any way they see fit.
But when you use the data, you need to understand that 20 strokes in our test is much less wear than 20 strokes in a CATRA ERT test.
I hope this is helpful in explaining our testing methodology. It's different from CATRA ERT for a reason, and the reason is
not to make FFD2 blades look better; it's to try to better measure the user experience.
Thanks,
Carl
There you go trollin' again Bill.
