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Thread: Advice on reshaping & sharpening an Usuba knife

  1. #11
    Quote Originally Posted by ThEoRy View Post
    They want to see a spine shot.
    Ok, thanks for the help. Here are some spine (& edge) shots:













    So far it kinda looks straight as far as I can say...

  2. #12
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    JBroida's Avatar
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    it does not look straight to me... also, laying a knife flat on something else flat does not always indicate a straight or not straight blade... there are a number of ways something can be not straight. In the second picture you can clearly see the bend that is causing your hole in the middle of your blade. It doesnt seem like it exists along the spine, making it a much more difficult bend to fix.

  3. #13
    Quote Originally Posted by TB_London View Post
    Very briefly, when you heat treat a steel the quench is intended to "lock" the structure. It's the carbon that allows that to happen, and as mild steel has a low C content it doesn't happen. With single sided laminates, there are stresses introduced where the high C steel is only supported on one side. This creates a tendency for the blade to warp/twist. The high C steel is slightly longer post HT than pre, and the mild doesn't really change.
    The grinding will also affect the internal stresses causing the knife to bend/twist as these are released.

    Keeping it straight involves more skill and steps in the process, which costs more money. So cheaper single bevel knives are more prone to being out of straight.

    If you hold your knife by the handle edge up and look down it does it look straight? Try the same spine up?

    If the knife has a bend or twist in it, when you sharpen it you can end up with gaps in the board contact like in your picture. Where Usuba's have an almost flat edge it's more of a problem.
    Thank you, that's a very clear explanation. I guess it is still kind of straight by now... Who knows how it will look after I've tried grinding the gaps out of it.

    It is definitely a problem since the gaps just make it annoying knife to work with: when trying needle cuts for example, the needles aren't completely separated from each other.

    I've took some additional photos from the side of the blade, but I find it hard to take good pictures that show how straight or bent it is.






  4. #14
    That one will be very hard to fix :P Like Jon say second picture really show it all. The main bevel is bend

  5. #15
    If there's a bend, I don't see it, 2nd photo looks pretty straight to me (I think the reflection of the darker wood grain is causing an optical illusion). If it is bent, something that subtle wouldn't be enough to cause the hole. How much have you sharpened it? I suspect you're spending too much time on the middle of the blade.

  6. #16
    Senior Member Brad Gibson's Avatar
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    im having a similar problem sharpening my gesshin uraku kama usuba. ive found a high spot in mine and would like some direction. preferably from jon.
    "A recipe has no soul. You as the cook must bring soul to the recipe." -Thomas Keller

  7. #17
    Hi All, thanks for all the replies. I realize it is very hard to show if it's straight or not.

    I guess JBroida & Maxim refer to the bend shown in this photo:


    My inexperienced eye would say the main bevel/blade is definitely not straight in a sense that the edge has high and low parts as indicated in the first post. If this is caused by a bend of the whole blade in the "left-right direction" is hard for me to say (see cartoon). It is even harder to take a good and clear photo.

    Cartoon: it is definitely not 'up-down-straight', but so far it seems 'left-right-straight' to me:



    I haven't really sharpened it that much, I guess it pretty much arrived like this. I'll try to sharpen/reshape it is little more (after all I purchased this as a practice usuba), and I'll keep you up-to-date.

  8. #18
    i meant this picture.

    Click image for larger version. 

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    you can actually see it bend a bit in 2 places
    And it also show in your scratch patterns on the main bevel

  9. #19
    Ah, ok. I get it now. Yeah, it is noticeable. Hard to see for me, but you're right.

    So basically I guess there isn't anything I can do to fix this type of bended knife, right? I guess flattening it out using a large bench vice would't do the trick? ;-)

  10. #20
    I had couple Usubas with same issues. I have never been successful in fixing it right There will always be a small gab. Specially where there is 2 bends that make it even more tricky.

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