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Effect of the Kangaroo Tail Strop on Sharpness

Discussion in 'Maintenance, Tinkering & Embellishment' started by wootzblade, Jun 8, 2019.

  1. wootzblade


    Feb 24, 2014
    Our recent video covers all known effects of stropping: de-oxidation, re-aligning, burnishing and wire-edge removal (we call it "de-wiring").

    It's a commonplace that a bare leather strop, i.e. the strop by itself without honing compounds, can improve sharpness of mainstream stainless steel and carbon knives.
    What really amazes me is the improved sharpness of premium wear-resistant blades. In addition to the CPM S35VN shown in the video I've tested other high vanadium steels, and every time see improved sharpness after as little as 6-10 strokes on the plain kangaroo tail strop, but never as much as on the S35VN knife.
    In my Knife Deburring book the S35VN steel is classed as "positive burr"; on these steels stropping can burnish a razor-sharp strip of steel over its vanadium-carbides at the apex.

    My interpretation of what we see in this video, in the order of appearance:
    #1 s/s Victorinox SWIBO - stropping removed oxidation from the edge, yielding 20 BESS improvement in sharpness - this is typical of an edge that is not rolled and is cleanly deburred.
    #2 s/s Fury - this used knife had a rolled edge, the stropping has aligned the edge, improving sharpness by near 2 times.
    #3 CPM S35VN - stropping burnished a razor-sharp strip of steel over its vanadium-carbides at the apex.
    #4 Carbon Japanese knife - the knife had a wire edge, that was removed by high-angle stropping, resulting in the dramatic improvement of sharpness.

    Sharpness Chart >>
    Last edited: Jun 8, 2019
  2. j_d


    Jan 14, 2006
    This was a very nice objective test.
    Any thoughts on 3v?
    Any thoughts on using cow leather glue do a board instead of kangaroo tail?
    Last edited: Jun 9, 2019
  3. wade7575


    Apr 3, 2013
    I'm not sure if you seen Kangaroo tail leather versus other leathers but Kangaroo tail is bumpy,I got a bunch of Kangaroo leather one time and the guy threw in some tail leather.

    I'm thinking the bumpiness must be what's having the affect.

  4. j_d


    Jan 14, 2006
    I have not seen it. Regrettably there is a shortage of kangaroos to hunt in Ohio. Thanks for the info. It makes me wonder if ray or shark skin would work too.
    Getting older likes this.
  5. wade7575


    Apr 3, 2013
    You can get Kangaroo leather off ebay fairly cheap.

  6. wootzblade


    Feb 24, 2014
    "Positive burr" knife steels we strop on a hanging strop, while "negative burr" on a firm strop.
    For example, s/s mainstream knives benefit from a higher-angle stropping, and we finish sharpening them on the hanging strop.
    On the other hand, well hardened higher-end steels are better finished on a firm strop, e.g. glued to a wooden block.

    Can only say that it was a somewhat unexpected finding even to myself how well the roo tail improves sharpness.
    I've been using horse strops, and 've seen them improving the edge by 20 BESS, and since 20 BESS is half of the edge apex width of a disposable shaving razor, it was about the edge keenness rather than sharpness.
    But when I see 100s of BESS improvement, it is significant, and those who sharpen knives themselves and also have the same sharpness tester seem to appreciate that.
    Eli Chaps and j_d like this.
  7. j_d


    Jan 14, 2006
    Thank you for the excellent post. I now have that sharpness tester and some tail leather on my list of things I'd like to own.
  8. wootzblade


    Feb 24, 2014
    I'd say that the takeaway for areas with the shortage of kangaroos is not to neglect bare leather hanging strops in knife sharpening.
    In our workshop, it has proved extremely beneficial as the finishing step in deburring mainstream knives, stainless steel and carbon.
    The hanging strop takes the knife edge to a new level of keenness, unattainable by edge-leading deburring, and where the firm strop can form a wire or foil edge, the hanging strop will not.
    Last edited: Jun 10, 2019
  9. wootzblade


    Feb 24, 2014
    BTW, did you know, that only a percentage of kangaroos have a tail long enough to cut out a single 50-60 cm hanging strop?
    It takes a whole kangaroo to harvest a single tail strop, and not every roo is good for that.
    A licensed roo shooter skins 40 kangaroos a day, yielding only under 10 tail strips long enough to make a hanging strop.

    Kangaroo tail is different to the kangaroo skin; knives stropped on the kangaroo tail stay sharp for longer than those stropped on its skin. This is sort of a factual knowledge in Australia; my explanation is that the edge gets deburred better on the tail leather, but whatever may the explanation be, their tail leather makes better strops for fact.
  10. Wowbagger

    Wowbagger Basic Member Basic Member

    Sep 20, 2015
    I keep being curious about all this high tech stropping business. I've already spent a great deal of time using low tech stropping (rough side up and or diamond on maple) and have written that off completely as a waste of time. I get better (more useful) edges FASTER off the best quality water stones.

    That said with the S____V(N) steels I have found that the very last thing I want is to burnish steel out in front of the vanadium carbides. Sure it cuts, curls, whittles hair. Big deal. That is easily done with a low hardness, plain carbon or low alloy steel like Case SS, CV or SAK. Whittles hair all day in both directions.

    Why I don't like the uncut carbides with burnished steel around them is as soon as I take say an S110V blade to some challenging material such as dusty rubber coated cloth or solid hard rubber the edge distorts and the actually useful cutting ability plummets within a day. In comparison the same steel sharpened with diamonds and refined and debured only on stones (in a jig) to 8,000 DMT Aligner lasts at the same work, done for short periods nearly every day, for weeks.

    My experience is the Plain High Carbon Steel benefits from stropping more than the sophisticated alloys.
    Again this is cutting not single hairs but as a work knife.
    Mr.Wizard and HeavyHanded like this.
  11. Wowbagger

    Wowbagger Basic Member Basic Member

    Sep 20, 2015
    Thank you . Once I woke up and realized the strop belt wasn't going to be glued down I wrote it off.
    I go out of my way to keep my stones flat and avoid the lumpiness of leather only to be shown leather with a bumpy curved surface (kangaroo).

    The very best hard working edges I have produced, used to cut very hard and often silica contaminated hard woods, have been the edges that I got the most accurately flat beveled / accurate edge geometry (not rounded over from hand sharpening, sloppy jig use or . . . stropping. Seriously I want an edge that is a line (of almost infinite thinness) but a line rather than a wavy thing. That was mostly with A2 steel which wasn't particularly hard or high alloy.

    I'm not going to be found stropping my M4, M390, or CTS-XHP on a curved belt.
    So part of why the tail is great is it is full of grit from being dragged on the ground by the animal ? Or what ? Wouldn't it be preferable to use a cleaner material and add more symmetrically graded grit to that ?
    Motega likes this.
  12. Wowbagger

    Wowbagger Basic Member Basic Member

    Sep 20, 2015
    + 1
    It was very effective considering the leather had no additional abrasive added.
    I'll keep that in mind.
    Still addicted to stones and jigs.
    Who knows what the future holds for my sharpening adventures . . . just when I'm ever so slightly tipping toward Wicked Edge you show this ! :eek:
    :mad: But I want to buy more . . . expensive gear :mad:
  13. wootzblade


    Feb 24, 2014
    Kangaroos are cuties, I would never be able to shoot one. But let's forget about them for a moment.
    Do not see this video as kangaroo-specific. My intention was to get some insight into hanging strop effects on the edge.

    The hanging strop is different to a firm strop, and you can see this difference with horse and cow strops as well, though to a lesser degree. While firm stropping can form a wire/foil edge on the apex, the hanging strop will not.

    Hanging strop is for use mainly with mainstream knives and straight raizors (which are also of mainstream steel).
    Where, for whatever reason, you hone mainstream knives on firm strops, you will get better edge by finishing the stropping on a hanging strop.

    With mainstream knife steels, the hanging strop prevents the wire edge, and if it is already there can eliminate it.
    With wear-resistant "supersteels", if the wire edge is on the apex, the hanging strop can turn it into a firm structural continuation of the apex steel matrix - at least this is how I interpret what I see on the sharpness tester. And this strip of steel matrix over the wear-resistant carbides at the apex is denser and stronger than anything we see in mainstream steels - we have many reliable indications of that.
    Last edited: Jun 11, 2019
    Eli Chaps likes this.
  14. CasePeanut

    CasePeanut Gold Member Gold Member

    May 25, 2018
    I wonder if there is a similar difference between (the much more widely available) smooth cow hide vs. rough hide. I've been playing with a homemade stropping block made from the rough side of a leather belt with 0.1m diamond paste. Despite the bumpy surface it appears to be deburring fairly evenly across the entire blade using high angle passes. Sadly I don't have a BESS tester to measure the difference.
  15. wootzblade


    Feb 24, 2014
    CasePeanut, that's how we see it as well, the rough side is for deburring.
    I believe the video and my comments to it partially address when to use the rough side of the leather strop - we go for it when see signs of a wire edge on a sharpened knife, and when a used edge is rolled - in these cases the rough side is very beneficial and improves SHARPNESS.
    The smooth side is for improving KEENNESS of the edge, de-oxidation and fine realigning of the edge.
    CasePeanut likes this.
  16. Ocelot85


    Feb 1, 2012
    This is just speculation, I'm not at all familiar with Kangaroo's being from the USA myself but could the tail provide a better strop because of micro-abrasives / dirt / dust embedded in the hide? It would essentially act as a fine stropping compound. It looks like their tails drag on the ground fairly often, I imagine a lot of fine grit would get worked into the hide.
  17. brando555


    Sep 26, 2018
    I'm curious about this tail leather now. I've got a couple edge pro strops with roo leather, but it is super smooth.
  18. wootzblade


    Feb 24, 2014
    Yes, the kangaroo skin is smooth, while the tail has a palpable cross-texture; the difference is the same as between the human skin and sole. The older the animal, the more pronounced is that texture; the roo puts its weight on the tail all the time, I guess that might be the reason.

    Its stropping effect might work along the principle of the HeavyHanded's Washboard Sharpening System

    Last edited: Sep 10, 2019
    brando555 likes this.
  19. cudgee

    cudgee Gold Member Gold Member

    May 13, 2019
    I have never seen the washboard system before. Very interesting, what is your opinion of this system?
  20. wade7575


    Apr 3, 2013
    If you look at the second picture in the ebay listing and however your mouse's hand over the picture to zoom in,you will be able to see that it's the outside of the tail and look at the texture of the leather.



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