Brian,
Excuse me if I'm extremely skeptical about those results.
No apologies needed. Skeptical is good! Good scientific work stands up to peer review. As I've seen quoted on another forum, "One person sharpens another."
... Maybe Cryano is not holding his test samples exactly parallel to the base of the BGA, which is required in order to produce accurate angles. This is a machine that uses a human to hold the work, and is therefor subject to the limits and perceptions of the human. What seems level by eye might not be all that level.
Without doubt, this factor can and does contribute variation in this experiment. However, the goodness of fit for the linear regressions provides strong evidence that the total variation introduced by this factor (in combination with all others) is insignificant.
Or perhaps the introduction of SQUARE stock to a flexible belt massively changes the grinding angle due to the geometry. Testing on blades that already have actual edge bevels would seem to be a more realistic test.
I agree: the geometry of the thick bar stock differs from that of the actual knife edges which have a primary bevel. I believe the important factor here is not the cross-sectional shape of the blade (rectangular for the bar stock vs. triangular for the typical knife), but the thickness of the blade stock at the point of contact with the belt, as this is the only point on the blade's cross-section which determines the amount of belt deflection.
I also agree that testing on blades which have a primary bevel is a more realistic test because it puts the test in a regime of blade stock thickness which is typical of common uses, and in which the offset between setting and results is less significant.
I find it very very hard to believe that WorkSharp would produce a product with enormous errors in it's indicated angle.
As I see it, there are no "errors" in the WorkSharp product; rather, it is remarkably accurate and precise. For thin blade stock, there is no offset at all: dial in 15 dps and you'll get 15 dps.
Even if the error is "only" 50% and a 17 degree per side edge becomes 25.5 degrees per side, that doesn't seem reasonable to me.
Theory proposes, experiment disposes.
I've put forth experimental data which are repeatable, reproducible, self-consistent, and which fit a plausible physical model. To my mind, that forms a reasonable explanation.
Again, we're not debating philosophy here, we're attempting to do science. I'd be delighted if any new data are presented which offer more insight into this phenomenon.
Maybe I'm wrong about all this and the BGA is fundamentally flawed and inaccurate. But I don't think so.
Again, these results do not support the assertion that the BGA is inaccurate; quite the opposite. The BGA is demonstrably accurate and precise.
Whether or not the BGA is flawed is a matter of opinion. In my opinion, the BGA is an excellent tool, capable of producing sharp edges on almost anything quickly and easily. As with all tools, one must understand how it works in order to get the most value from it.
Tony