10-31-2018, 01:40 PM
Well, I was starting to lean the other way, thinking that you are right about the rounding, and that my conjectures were just a flight of fantasy. But since you're seeing it, I'm now even more curious.
A sharp 90-degree-inclusive edge cuts easily (I've sliced myself on the planed corners of boards often enough), though not deeply. I have a plane blade that's sharpened at 90 (it's a scraper blade), and it gets nice, clean shavings, albeit thin. It never feels that sharp to me, but it cuts like it's sharp, so I think that the "media" used to check sharpness (my fingers, in this case) don't allow much penetration at that edge angle, hence the perceived difference. Might be interesting to test that blade on the BESS tester.
I believe that for any given abrasive/grit, the edge will be toothier as the edge-angle decreases, which would lead to it feeling sharper, and possibly passing some sharpness tests easier, but that wouldn't necessarily impact the BESS score. With the precision and repeatability of your sharpening methods, the only difference I would expect to see there is that you might have to go to a finer grit for the low angle bevels, but that seems opposite to your conclusions, so there must be more to the story.
To your comments about the whole width being abraded at 90 degrees, I've spent some time trying to visualize the differences, and coming up short. When I have one of those boards I'm planing, if I take another shaving I still have a sharp corner, just a thinner board. I have no idea what the apex radius is in that case, but I don't think it changes much. I would expect the same to be true to some extent with abrasives and steel, and my understanding is too weak to speculate on how/where they would differ. One area where I can visualize it being an issue is that I use mostly edge-leading strokes when sharpening, so perhaps the behaviour of the slurry is to dull more obtuse angles more easily, but that doesn't explain your observations, since (I think) your sharpening is all edge-trailing.
I doubt there's any practical consequence to all of this conjecture, but thanks to your message I'll be dreaming about 90-degree edges for the next few nights. And I'll put my scraper blade on the BESS tester next time I sharpen it, which will probably be this weekend.
A sharp 90-degree-inclusive edge cuts easily (I've sliced myself on the planed corners of boards often enough), though not deeply. I have a plane blade that's sharpened at 90 (it's a scraper blade), and it gets nice, clean shavings, albeit thin. It never feels that sharp to me, but it cuts like it's sharp, so I think that the "media" used to check sharpness (my fingers, in this case) don't allow much penetration at that edge angle, hence the perceived difference. Might be interesting to test that blade on the BESS tester.
I believe that for any given abrasive/grit, the edge will be toothier as the edge-angle decreases, which would lead to it feeling sharper, and possibly passing some sharpness tests easier, but that wouldn't necessarily impact the BESS score. With the precision and repeatability of your sharpening methods, the only difference I would expect to see there is that you might have to go to a finer grit for the low angle bevels, but that seems opposite to your conclusions, so there must be more to the story.
To your comments about the whole width being abraded at 90 degrees, I've spent some time trying to visualize the differences, and coming up short. When I have one of those boards I'm planing, if I take another shaving I still have a sharp corner, just a thinner board. I have no idea what the apex radius is in that case, but I don't think it changes much. I would expect the same to be true to some extent with abrasives and steel, and my understanding is too weak to speculate on how/where they would differ. One area where I can visualize it being an issue is that I use mostly edge-leading strokes when sharpening, so perhaps the behaviour of the slurry is to dull more obtuse angles more easily, but that doesn't explain your observations, since (I think) your sharpening is all edge-trailing.
I doubt there's any practical consequence to all of this conjecture, but thanks to your message I'll be dreaming about 90-degree edges for the next few nights. And I'll put my scraper blade on the BESS tester next time I sharpen it, which will probably be this weekend.