07-27-2020, 07:35 PM
Great image! Thanks for posting it and reviving this thread. Once you know what to look for and understand what the image shows a rolled edge is obvious. That is a excellent example.
I know many folks who are not sharpeners think that edges dull due to abrasion, like the edge is worn away. Unless the edge is used to cut abrasive material such as sandpaper, we know that edges dull because they roll. Your image shows shows that rolling clearly.
It makes sense to think that harder steel like HRC 60+ would be more resistant to rolling, but EOU SET testing demonstrated that hard steel rolls just as much. Additionally hard steel has the downsides of being harder to sharpen and more prone to chipping. There is a reason why the major knife manufactures like Henckel, etc., generally use steel in the HRC 56 - 58 range.
From everything I've seen, our super sharp edges are so thin they roll regardless of steel hardness as show in that image. I like to explain it as the bulldozer and egg syndrome. A bulldozer lowered onto an egg will crush it. Same for a dozen eggs even they should be able to support 12X more weight. Slightly harder steel just can't compensate for the forces involved with everyday knife use.
Want to see something cool? Use the corner of a razor blade or Exacto blade and slide it up the side of the bevel and push the bottom of the roll up and over the edge. Then take a microscope image of it. It will show very clearly how that roll is bent over metal. It's strange, but you can actually push that roll up. It's actually pretty wimpy and thin.
Mr. Cyrano, that's a nice image. What microscope did you get? What magnification? Bright-field or dark-field lighting? I notice there are not any rainbow reflections so often seen with microscopy of steel. Did you use a polarizer?
I know many folks who are not sharpeners think that edges dull due to abrasion, like the edge is worn away. Unless the edge is used to cut abrasive material such as sandpaper, we know that edges dull because they roll. Your image shows shows that rolling clearly.
It makes sense to think that harder steel like HRC 60+ would be more resistant to rolling, but EOU SET testing demonstrated that hard steel rolls just as much. Additionally hard steel has the downsides of being harder to sharpen and more prone to chipping. There is a reason why the major knife manufactures like Henckel, etc., generally use steel in the HRC 56 - 58 range.
From everything I've seen, our super sharp edges are so thin they roll regardless of steel hardness as show in that image. I like to explain it as the bulldozer and egg syndrome. A bulldozer lowered onto an egg will crush it. Same for a dozen eggs even they should be able to support 12X more weight. Slightly harder steel just can't compensate for the forces involved with everyday knife use.
Want to see something cool? Use the corner of a razor blade or Exacto blade and slide it up the side of the bevel and push the bottom of the roll up and over the edge. Then take a microscope image of it. It will show very clearly how that roll is bent over metal. It's strange, but you can actually push that roll up. It's actually pretty wimpy and thin.
Mr. Cyrano, that's a nice image. What microscope did you get? What magnification? Bright-field or dark-field lighting? I notice there are not any rainbow reflections so often seen with microscopy of steel. Did you use a polarizer?