05-31-2017, 09:57 PM
I was wondering why I was not seeing more of a correlation between an increasing aggressive and toothy edge when I sharpen with a significantly coarser belt abrasive. My guess was that is was due to the fact that I apply very light knife to belt pressure when I sharpen. I really don’t push against the belt hard at all, and generally see little or no belt deflection using medium weight belt.
Of course a toothy edge is directly related to the depth of bevel scratching caused by the abrasive. It only stands to reason more pressure would cause the abrasive to more deeply penetrate the steel, and that light pressure would have less penetration. This obviously results in more metal removal with more pressure than with less.
I sharpened the blade using a 120 grit almost new SiC belt applying light pressure like I usually do and produced a dandy burr:
Then I removed the burr:
Even though I was not concerned about how sharp the blade was the PT50B was just sitting there so why not? Approximately in 1/3 increments along the blade from handle to tip the sharpness readings were:
210
225
205
That seemed a bit dull from what I’m use to seeing so I gave it about 10 strops on my jeans across my thigh just to remove any crud that might still be on the edge. Then I measured sharpness again:
170
170
190
Well, huh. I wonder what that means?
Then I sharpened again, this time applying considerably more pressure on the belt and then performed an apparently sloppy job of burr removal. I could not see or feel a burr so I figured I was good to go, but as you, dear reader , will soon see, that was a most spurious assumption. The two images are the same, just different lighting:
Now here’s the freaky part. It demonstrates not only the importance of complete burr removal but additionally just how deceptive a burr can be. Furthermore, it illuminates how the combination of both a sharpness tester and a microscope complement and verify the empirical data provided by the other. Even with all that obvious burr crud piled up on the edge of the blade, the sharpness readings were:
160
180
160
A bit of a head scratcher, eh?
Here’s the direct comparison. You can observe how increasing pressure produces more frequent and deeper scratches:
As always with my tests, take from it what you will. This was just one test and is neither extensive or conclusive. Hope you found it interesting.
Of course a toothy edge is directly related to the depth of bevel scratching caused by the abrasive. It only stands to reason more pressure would cause the abrasive to more deeply penetrate the steel, and that light pressure would have less penetration. This obviously results in more metal removal with more pressure than with less.
I sharpened the blade using a 120 grit almost new SiC belt applying light pressure like I usually do and produced a dandy burr:
Then I removed the burr:
Even though I was not concerned about how sharp the blade was the PT50B was just sitting there so why not? Approximately in 1/3 increments along the blade from handle to tip the sharpness readings were:
210
225
205
That seemed a bit dull from what I’m use to seeing so I gave it about 10 strops on my jeans across my thigh just to remove any crud that might still be on the edge. Then I measured sharpness again:
170
170
190
Well, huh. I wonder what that means?
Then I sharpened again, this time applying considerably more pressure on the belt and then performed an apparently sloppy job of burr removal. I could not see or feel a burr so I figured I was good to go, but as you, dear reader , will soon see, that was a most spurious assumption. The two images are the same, just different lighting:
Now here’s the freaky part. It demonstrates not only the importance of complete burr removal but additionally just how deceptive a burr can be. Furthermore, it illuminates how the combination of both a sharpness tester and a microscope complement and verify the empirical data provided by the other. Even with all that obvious burr crud piled up on the edge of the blade, the sharpness readings were:
160
180
160
A bit of a head scratcher, eh?
Here’s the direct comparison. You can observe how increasing pressure produces more frequent and deeper scratches:
As always with my tests, take from it what you will. This was just one test and is neither extensive or conclusive. Hope you found it interesting.