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Thread: Cutting comparison between s30v/superblue rough vs refined edge

  1. #1
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    Cutting comparison between s30v/superblue rough vs refined edge

    I made an interesting discovery today about edge finishes. I am well aware that a lower grit, less refined edge can have better cutting ability than a more refined edge. For this reason I tend to finish my high carbide steels at medium grits, but I still like to polish some of my edges (like superblue) just to achieve those "novelty edges" that will grab and break a hanging hair even though they won't perform as well at mundane tasks like cleaning fish.

    Anyway, I have always been under the assumption that the rougher edge would outperform while pulling across material because of the micro serrations but I assumed the polished edge would still outperform in straight push cuts. Well, today I was getting my fishing gear together and I had my yojimbo and sb caly sitting on the table. They are both as sharp as I can get them. The yojimbo finished lightly on the medium rods has tons of bite, and the caly polished on the uf rods will break even my fine hairs in half at the touch. So when I went to cut my 50 lb braided line, I decided to compare the two. The results were not really what I expected.

    I held the line tight against the side of the blade with my thumb and with the other hand I pulled the line straight against the edge. I did the exact same cut numerous times with each knife. What I found was that the hair splitting edge of the caly required me to put 2-3 times as much pressure on the line as the rough finished s30v yojimbo. Now if I had been "pulling" the edge across the line I would have expected this result, but the way I was just putting straight pressure against the edge, I kind of expected the refined edge to push through he braid easier. It did not! It wasn't even close.

    Anyway, nothing scientific, just a real world observation and I just thought the results were interesting. The more I learn, the more I realize there is very little work that I do with a knife that benefits from a refined edge. I still keep a couple of knives polished just because I like whittling hairs and just seeing how fine I can get an edge, but my medium finish edges outperform them in just about every way.

    EDIT: I just went back and performed the same test with 80lb monofilament and got different results. It was very close, but the polished edge cut through the monofilament slightly easier than the medium finish s30v. The results I got on the braid might have been due to how the micro serrations interacted with the microfibers of the braided line? Paging Cliff?? Hehehe
    Last edited by Surfingringo; 04-14-2014 at 03:34 PM.

  2. #2
    Spyderco Forum Registered User 3rdGenRigger's Avatar
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    The differing blade geometries between the two will also affect performance.
    Last edited by 3rdGenRigger; 04-14-2014 at 03:47 PM. Reason: Typo
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    Spyderco Forum Registered User Jazz's Avatar
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    Yep. Cool, and thanks for sharing. I only use polished edges on wood carving knives. Wayne Goddard taught me that in Blade magazine, plus, I noticed they seemed useless on some things, even though hair splitting sharp. I'm not impressed at all by all the "shiny-edged" pics I see. I finish fine with a wee raised edge the last couple strokes, then a light strop to get rid of the wire.
    - best wishes, Jazz.

  4. #4
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    Quote Originally Posted by 3rdGenRigger View Post
    The differing blade geometries between the two will also affect performance.
    Yes, but not in this test since the diameter of the line is smaller than the depth of the edge bevel.

  5. #5
    Spyderco Forum Registered User Donut's Avatar
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    It could be the straight edge applying more pressure against the line than the curved edge. Are you sure you were applying the pressure directly perpendicular to the edge?

    Thanks for sharing the results.

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    I retried the test and got more results. The braid I was originally cutting has been on the reel for almost a year and the fibers are showing some fraying and are generally looser than when new. I tried the test again (being even more precise to make sure I was holding it completely perpendicular) and got the same results. However, I also got out some brand new braid and performed the same test. On the new braid, the fibers are extremely tight and the two knives performed similarly. So it is only on the worn, more loosely woven braid that the rougher edge of the yojimbo far outperforms the caly. Like I said in the op, if I was pulling the edge across the line, this would make perfect sense, but on a straight perpendicular "pushcut" like I am doing I still find the results surprising.

    Ahh, and the sb caly is the 3.5. I like it a lot!

  7. #7
    Spyderco Forum Registered User Holland's Avatar
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    interesting observations
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    Maybe the larger scratches on the coarser Yojimbo edge trapped the loose braid fibers so they couldn't spread out along the edge. If so, maybe the Yojimbo cut the individual fibers sequentially instead of letting them spread out to "gang up" on the polished edge so it had to cut more of them at once? Divide and conquer? This theory would explain why your experience push cutting the monofilament was different, as was the tighter braid of the newer braided line.

  9. #9
    Spyderco Forum Registered User senorsquare's Avatar
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    It would be interesting to try them both with the same coarse edges. That might shed some light on what role difference in geometry is playing.

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    Quote Originally Posted by Bill1170 View Post
    If so, maybe the Yojimbo cut the individual fibers sequentially instead of letting them spread out to "gang up" on the polished edge so it had to cut more of them at once?
    A mono line is cut much the same as wood is cut, it is just a continuous media so if you cut it on a push you would expect a higher polish to produce a lower force. Critical here is that the fine polish on the edge isn't one which is rounded over but actually still very sharp, at a minimum for example does it cut a tomato as soon as you draw it across it or does it slip a little.

    Braided lines are very different as they are not one continuous medium and they are designed to strongly resist abrasion in general. What you have proposed is I believe one of the main critical differences. If you want to see it on a larger scale take a serrated vs plain edge knife to a cut resistant glove and watch what happens.

    I would assume what is happening is similar to :

    -the coarse teeth on the plain edge knife will puncture the braided line directly or indirectly
    -as the line is pushed apart by the puncture there is very high localized pressure around the teeth which produce a cutting action
    -this causes the line to open up and the process can repeat

    This won't happen on a mono line as it will just smear out completely and fill in all the spaces and this high localized pressure isn't created and you would then just end up trying to push basically a saw through a piece of wood by using a very coarse edge on them in a push.

    Quote Originally Posted by Surfingringo View Post

    Anyway, nothing scientific, just a real world observation ...
    Science is made from real world observations in part, there is nothing unscientific about what you did. In general it is impossible to conduct an unscientific observation or experiment, where a body of work tends to move from science is when conclusions are reached which can not be supported from the observations they are based upon.

    For example if you had concluded that in general coarse edges are superior to push cut braided lines then you would be stretching the validity of your observations (as there are other possible influences), however making observations and raising questions, repeating the work to try to understand - that is science.

  11. #11
    Spyderco Forum Registered User dgebler's Avatar
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    Interesting testing and as always great to hear from Cliff on this subject. As a layperson with limited understanding of the science behind the steel I love so much it is always an interesting read for me and for the most part broken down in terms I can understand and appreciate. Here's to real world observations contributing to our collective understanding of knife geometry, steel and the beauty of sharp edges.

  12. #12
    Spyderco Forum Registered User xceptnl's Avatar
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    Quote Originally Posted by Cliff Stamp View Post
    ...Braided lines are very different as they are not one continuous medium and they are designed to strongly resist abrasion in general. What you have proposed is I believe one of the main critical differences. If you want to see it on a larger scale take a serrated vs plain edge knife to a cut resistant glove and watch what happens.
    This is what I was imagining when reading Lance's description. Basically it all comes back to the fact that the edge can be optimized for the intended media. Based on these results, your hair has a diameter less than distance between the peaks of the micro serrations. This essentially negates the micro serrations and the contact area is the same as the more polished edge.
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