As I mentioned in the thread about my YouTube videos, I'd recently noticed something unexpected on my two Spyderco PM2's in CPM-M4 (yes, I bought both the BladeHQ and Knifeworks dealer exclusives): I'd shaped the edge bevel on one of them using a King 1000 and then set an apex microbevel using Spyderco M rods, and I quite liked the balance of push-cutting sharpness and slicing aggression I got, so I decided to replicate the finish on the other one.
I shaped the edge bevel of the other one using my Sigma Power Select II 1000 and then again set an apex microbevel using my Spyderco M rods. Imagine my surprise when the apex on the second knife turned out significantly finer (more push cutting sharpness, less slicing aggression) than the first, even though both blades had identical steels and virtually identical geometries.
The first thing I did was examine both edges under my USB microscope, and it was apparent that the edge bevel that had been shaped on the King 1000 showed a much more directional (i.e. vertical up and down) scratch pattern than the edge bevel that had been shaped on the SPS-II 1000, which showed a much more randomized scratch pattern.
I also double checked that the difference hadn't just been an aberration by cutting off the apex that I had just set on the second knife which I'd used the SPS-II 1000 on and re-shaped the edge bevel on the King 1000, and again applied an apex microbevel using my Spyderco M rods. This time, I obtained very similar balance of push cutting sharpness and slicing aggression to the first knife, and under my USB microscope, the scratch pattern on the edge bevel appeared similarly directional to the first knife.
I had an intuition as to what had caused the difference, and I decided to investigate it further by taking one of my Calton Cutlery 1095 neckers and shaping the edge bevel on it on both the King 1000 and SPS-II 1000, while altering how much of a slurry was on the stone when I started.
In all cases I flattened the waterstone immediately prior to use, and only varied whether I deliberately raised a thick mud, only did enough work to flatten the stone, or rinsed off the slurr left from flattening prior to use. In all cases my passes were made with complete heel to toe back and forth passes using low force.
Also note that all microscopic images are taken with a USB microscope with 50x optical and 4x digital zoom, at max combined zoom.
The first image is of the edge bevel as shaped on the King 1000 with a moderate amount of slurry on the stone. By moderate I mean the amount of slurry created by flattening the stone without working extra to deliberately create a thick layer of mud on the stone.
As you can see, even with a moderate slurry present, the King 1000 still creates a fairly directional scratch pattern.
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The second image is of the edge bevel as shaped on the Sigma Power Select II 1000 with a moderate amount of slurry on the stone from flattening.
By contrast, the scratch pattern here shows significantly less directionality and appears to have been much more affected by three-body abrasion.
I believe that this difference, which was even more pronounced on the two Spyderco PM2's in M4, explains why the one with the edge bevel shaped on the King 1000 showed more slicing aggression and less push cutting sharpness than the one with he edge bevel shaped on the SPS-II 1000.
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This third image shows the edge bevel as shaped on the SPS-II 1000, however in this case all slurry was rinsed off the stone prior to use.
As you can see, in this case the SPS-II 1000 produced a similarly directional scratch pattern to that which had been produced by the King 1000 above.
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This fourth image shows the edge bevel as shaped on the King 1000, however in this case I deliberate raised a thick mud on the stone well in excess to that I normally create when flattening my waterstones prior to use.
This time the King 1000 produced a much less directional scratch pattern than previously, and obviously shows much more evidence of three-body abrasion from the slurry on the stone.
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This final image shows the edge bevel as shaped on the King 1000, however this time I rinsed off any slurry present.
As expected, we see a very directional scratch pattern when the stone is used without a significant slurry.
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What was most interesting to me was that the King 1000 showed much less difference in the scratch pattern produced between no slurry and a moderate slurry than the Sigma Power Select II 1000 did. Only when a very thick mud was deliberately created on the King 1000 did it begin to produce a similar extent of three-body abrasion.
I have a conjecture as to why this is the case, based on information we already have about these two stones. We already know that the King 1000 uses aluminum oxide abrasive and a resin binder, while the SPS-II stones use much harder silicon carbide abrasive and have almost no binder:
This leads me to think that the slurry produced by the SPS-II stone contains a much higher density of abrasive particles, and those abrasive particles will be less likely to break down, leading to the slurry produced by the SPS-II 1000 to be more abrasive and induce much more three-body abrasion per volume of slurry than the slurry produced by the King 1000. Or at least, that's the best theory I can come up with to fit the available evidence.
It also serves as a great example of just how much the behaviour of waterstones can change based on how they are used. Just varying the amount of slurry created on the stone prior to use was able to create large differences in the scratch pattern obtained.
I shaped the edge bevel of the other one using my Sigma Power Select II 1000 and then again set an apex microbevel using my Spyderco M rods. Imagine my surprise when the apex on the second knife turned out significantly finer (more push cutting sharpness, less slicing aggression) than the first, even though both blades had identical steels and virtually identical geometries.
The first thing I did was examine both edges under my USB microscope, and it was apparent that the edge bevel that had been shaped on the King 1000 showed a much more directional (i.e. vertical up and down) scratch pattern than the edge bevel that had been shaped on the SPS-II 1000, which showed a much more randomized scratch pattern.
I also double checked that the difference hadn't just been an aberration by cutting off the apex that I had just set on the second knife which I'd used the SPS-II 1000 on and re-shaped the edge bevel on the King 1000, and again applied an apex microbevel using my Spyderco M rods. This time, I obtained very similar balance of push cutting sharpness and slicing aggression to the first knife, and under my USB microscope, the scratch pattern on the edge bevel appeared similarly directional to the first knife.
I had an intuition as to what had caused the difference, and I decided to investigate it further by taking one of my Calton Cutlery 1095 neckers and shaping the edge bevel on it on both the King 1000 and SPS-II 1000, while altering how much of a slurry was on the stone when I started.
In all cases I flattened the waterstone immediately prior to use, and only varied whether I deliberately raised a thick mud, only did enough work to flatten the stone, or rinsed off the slurr left from flattening prior to use. In all cases my passes were made with complete heel to toe back and forth passes using low force.
Also note that all microscopic images are taken with a USB microscope with 50x optical and 4x digital zoom, at max combined zoom.
The first image is of the edge bevel as shaped on the King 1000 with a moderate amount of slurry on the stone. By moderate I mean the amount of slurry created by flattening the stone without working extra to deliberately create a thick layer of mud on the stone.
As you can see, even with a moderate slurry present, the King 1000 still creates a fairly directional scratch pattern.
The second image is of the edge bevel as shaped on the Sigma Power Select II 1000 with a moderate amount of slurry on the stone from flattening.
By contrast, the scratch pattern here shows significantly less directionality and appears to have been much more affected by three-body abrasion.
I believe that this difference, which was even more pronounced on the two Spyderco PM2's in M4, explains why the one with the edge bevel shaped on the King 1000 showed more slicing aggression and less push cutting sharpness than the one with he edge bevel shaped on the SPS-II 1000.
This third image shows the edge bevel as shaped on the SPS-II 1000, however in this case all slurry was rinsed off the stone prior to use.
As you can see, in this case the SPS-II 1000 produced a similarly directional scratch pattern to that which had been produced by the King 1000 above.
This fourth image shows the edge bevel as shaped on the King 1000, however in this case I deliberate raised a thick mud on the stone well in excess to that I normally create when flattening my waterstones prior to use.
This time the King 1000 produced a much less directional scratch pattern than previously, and obviously shows much more evidence of three-body abrasion from the slurry on the stone.
This final image shows the edge bevel as shaped on the King 1000, however this time I rinsed off any slurry present.
As expected, we see a very directional scratch pattern when the stone is used without a significant slurry.
What was most interesting to me was that the King 1000 showed much less difference in the scratch pattern produced between no slurry and a moderate slurry than the Sigma Power Select II 1000 did. Only when a very thick mud was deliberately created on the King 1000 did it begin to produce a similar extent of three-body abrasion.
I have a conjecture as to why this is the case, based on information we already have about these two stones. We already know that the King 1000 uses aluminum oxide abrasive and a resin binder, while the SPS-II stones use much harder silicon carbide abrasive and have almost no binder:
This leads me to think that the slurry produced by the SPS-II stone contains a much higher density of abrasive particles, and those abrasive particles will be less likely to break down, leading to the slurry produced by the SPS-II 1000 to be more abrasive and induce much more three-body abrasion per volume of slurry than the slurry produced by the King 1000. Or at least, that's the best theory I can come up with to fit the available evidence.
It also serves as a great example of just how much the behaviour of waterstones can change based on how they are used. Just varying the amount of slurry created on the stone prior to use was able to create large differences in the scratch pattern obtained.