# Advice on reshaping & sharpening an Usuba knife



## BramM (Oct 14, 2013)

Hi All,

I've recently bought a (cheap) _usuba_ knife to practice some new techniques. I've got 2 question.

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Unfortunately I noticed the edge of the knife isn't straight: when the edge is placed on a flat surface some parts of the blade touch the table whereas other parts don't. This can clearly be seen in the following photo:







I guess I can just try to 'reshape' the edge (starting with a rough whetstone), but I expect this is going to be a pretty hard job. Is there a good 'standard' technique for this or does somebody has some good advice for me? 

--

Next to this, I have another related question: when sharpening the _usuba_ I place the entire 'blade path' (_kiriba_) on the whetstone when sharpening the front side. As I understood (correct me if I'm wrong), this (see cartoon below) is the way to sharpen a single bevel knife:






A problem arising from using this techniques seems to be that I introduce scratches on the 'blade path'/_kiriba_-part as pointed out by the red arrow in the photo below. I find these scratches unappealing, and would like to learn to sharpen a knife without scratching it in this way. 




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So my second questions is: can this usuba be sharpened without introducing these scratches or should these scratches be removed by polishing after sharpening? Or is this (cheap) usuba possibly just of low-quality and will these stains/scratches not appear when I sharpen an expensive usuba in the same way? :scratchhead:

thanks in advice!


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## TB_London (Oct 14, 2013)

The coarse scratches are removed by using finer abrasives which leave finer scratches. Have you checked the knife is straight? In my experience Cheaper usuba a are often slightly out of straight, which introduces waviness in the edge when sharpening.
Watch Jon from JKIs videos on YouTube for a primer on single bevel sharpening


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## Zwiefel (Oct 14, 2013)

BramM said:


> Unfortunately I noticed the edge of the knife isn't straight: when the edge is placed on a flat surface some parts of the blade touch the table whereas other parts don't. This can clearly be seen in the following photo:



I think the section toward the "tip" of the usuba usually isn't in the same line as the rest of the edge, so this seems normal to me. The gap towards the heel/choil of the edge isn't right though.

HTH,
Z


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## ThEoRy (Oct 14, 2013)

You have to sharpen it that way in order to maintain the knife's proper geometry as you remove steel and the edge rises up towards the spine. In addition when you sharpen the blade road you apply pressure directly over the shinogi line, then you sharpen while applying pressure directly over the lamination line, then you blend the two together. This creates a compound bevel called a hamaguriba which translates to clamshell due to it's shape. Finally you uraoshi sharpen which means to push the back side because you are only to apply slight pressure on the push so as to keep the ura even around the blade since pulling backwards naturally adds a downward force. As far as the scratches, you have to get some decent stones which leave that misty or kasumi look when finished. I use the gesshin 400- king 800- gesshin aoto on the blade road to achieve this then I finish the hagane and ura up to the rika 5k.


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## BramM (Oct 14, 2013)

TB_London said:


> The coarse scratches are removed by using finer abrasives which leave finer scratches. Have you checked the knife is straight? In my experience Cheaper usuba a are often slightly out of straight, which introduces waviness in the edge when sharpening.
> Watch Jon from JKIs videos on YouTube for a primer on single bevel sharpening



Thanks for the advice! The highest grid stone I have is a 3k, but I'm gonna see what I can do. What do you mean exactly with if the knife is straight? Does the first photo in my post not answer that question?


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## BramM (Oct 14, 2013)

Zwiefel said:


> I think the section toward the "tip" of the usuba usually isn't in the same line as the rest of the edge, so this seems normal to me. The gap towards the heel/choil of the edge isn't right though.
> 
> HTH,
> Z



Thanks; that is great information!


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## BramM (Oct 14, 2013)

ThEoRy said:


> You have to sharpen it that way in order to maintain the knife's proper geometry as you remove steel and the edge rises up towards the spine. In addition when you sharpen the blade road you apply pressure directly over the shinogi line, then you sharpen while applying pressure directly over the lamination line, then you blend the two together. This creates a compound bevel called a hamaguriba which translates to clamshell due to it's shape. Finally you uraoshi sharpen which means to push the back side because you are only to apply slight pressure on the push so as to keep the ura even around the blade since pulling backwards naturally adds a downward force. As far as the scratches, you have to get some decent stones which leave that misty or kasumi look when finished. I use the gesshin 400- king 800- gesshin aoto on the blade road to achieve this then I finish the hagane and ura up to the rika 5k.



OK. Thanks. I will get back to you later.. after I've read some more background info


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## JBroida (Oct 14, 2013)

is your blade straight (left to right)?


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## ThEoRy (Oct 14, 2013)

They want to see a spine shot.


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## TB_London (Oct 15, 2013)

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.


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## BramM (Oct 15, 2013)

ThEoRy said:


> 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...


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## JBroida (Oct 15, 2013)

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.


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## BramM (Oct 15, 2013)

TB_London said:


> 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.
> ...



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.


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## maxim (Oct 15, 2013)

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


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## spaceconvoy (Oct 15, 2013)

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.


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## Brad Gibson (Oct 15, 2013)

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.


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## BramM (Oct 15, 2013)

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.


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## maxim (Oct 15, 2013)

i meant this picture.




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


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## BramM (Oct 15, 2013)

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? ;-)


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## maxim (Oct 15, 2013)

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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## JBroida (Oct 15, 2013)

it can usually be fixed, but its hard... when i do this it takes A LOT of time


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## BramM (Oct 15, 2013)

I've spend the last 2 hours trying all kind of things using a coarse grit stone and I don't think it has improved. After a while I thought I noticed some improvement, but when I went to a finer grit stone, this turned out to be an illusion and the knife is now back to it bended shape. I guess I found the perfect excuse to buy a better knife in the future ;-)


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## JBroida (Oct 15, 2013)

warping problems can not be fixed on stones... stones actually make the problems worse most of the time


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## stevenStefano (Oct 15, 2013)

I had a knife like that and it just couldn't be fixed. That's why everyone says not be cheap when it comes to usubas


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## Dave Martell (Oct 15, 2013)

Even duct tape won't fix that mess.


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