Blade Flex and Sujis

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WildBoar said:
uh oh -- previous post needs moderator approval. I'm guessing theat's due to the link :(
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HUH?

Thanks for the info! It's something I'd never be able to answer by myself. Thanks for performing and sharing your experiments, Stephen. I love that!
 
tk59 said:
HUH?

Thanks for the info! It's something I'd never be able to answer by myself. Thanks for performing and sharing your experiments, Stephen. I love that!
Click to expand...
Sorry -- that was a reference to a post I had just made. It initially showed on my screen as pending, requiring moderator approval. Looks like it went into the ether now :-(
 
WildBoar said:
Sorry -- that was a reference to a post I had just made. It initially showed on my screen as pending, requiring moderator approval. Looks like it went into the ether now :-(
Click to expand...

Interesting. I wonder what sorts of posts need Mod approval... Is there a place to look that up?
 
Why would you desire flexibilty in a Suji (or any knife)?

I used to think flexibilty was a good quality in a boning/filet knife. Since I started using Japanese knives I no longer think that. The Deba and the Yani are the traditional Japanese Fish knives...no flex there.

There's no knife cut I'm aware of that requires the abilty to flex the blade.

I'm open to other views though...
 
Deflection is dictated by modulus of elasticity (which is a property of the steel), moment of intertia (which is dependent on the cross-section geometry), the length of the blade and the amount of the load.

Here is the formula for deflection assuming the load is at the end of the blade, which is the worst case (I tried pasting a link to this, but the forum software would not allow the post): deflection = (W*L^3)/(3*E*I)

W = load
L = length (of blade)
E = modulus of elasticity
I = moment of inertia

The modulus of elasticity is normally derived from a stress vs strain curve, so it is a true material property based on physical testing.
 
tk59 said:
Interesting. I wonder what sorts of posts need Mod approval... Is there a place to look that up?
Click to expand...
here is the site/ page; you'll have to piece it together:

dubdubdub dot engineersedge dot com forward slash beam_bending forward slash beam_bending9 dot htm
 
Wildboar, I had a post sent to moderation with a link once. Dave said it is just something wonky in the system and happens every now and then.

k.
 
Kentucky Jeff said:
Why would you desire flexibilty in a Suji (or any knife)?

I used to think flexibilty was a good quality in a boning/filet knife. Since I started using Japanese knives I no longer think that. The Deba and the Yani are the traditional Japanese Fish knives...no flex there.

There's no knife cut I'm aware of that requires the abilty to flex the blade.

I'm open to other views though...
Click to expand...

The ability to flex gives you an idea of how well the material will resist deformation. In use, flex is a problem but if you like thin, it's nice to have an idea of how thin you can make it without getting too much flex while cutting.
 
I think the depth of the deba blade makes for better hand clearance than a shallow filet knife; hence no flex needed; and the thickness creates the needed pressure to break the skin from the flesh. The flex of a filet helps to get the blade flat to the board without scraping your knuckles; also it creates pressure between the flesh and skin.

As a child I watched my grandfather, uncles and father filet millions of fish. A flexible filet was the standard; used on the face of a huge chopped down tree trunk...
 
Kentucky Jeff said:
Why would you desire flexibilty in a Suji (or any knife)?

I used to think flexibilty was a good quality in a boning/filet knife. Since I started using Japanese knives I no longer think that. The Deba and the Yani are the traditional Japanese Fish knives...no flex there.

There's no knife cut I'm aware of that requires the abilty to flex the blade.

I'm open to other views though...
Click to expand...


not to be picky about technicalities but "flexibility" is the ability to be bent repeatedly without injury or damage.

that I would think is a very desirable trait for a kitchen knife, no?

I think what you are asking is why you would want a knife to flex easily, and in general I would think the consensus is that you don't. however, you DO want a very thin knife to allow for ease of cuts and sharpening, the thinner the blade the more easily it will flex

It's more of the case of accepting flex as a byproduct of another trait that is more important than stiffness.
 
StephanFowler said:
It's more of the case of accepting flex as a byproduct of another trait that is more important than stiffness.
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Personally, I value stiffness more than many other qualities in a knife (could be because I'm not a very good sharpener), but, that's a great way to explain it Stephan.
 
tk59 said:
Interesting. I wonder what sorts of posts need Mod approval... Is there a place to look that up?
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We're experiencing a problem with posts made under the General category that includes links in the text being sent to the moderation que. It's an intermittent problem though, across different user groups, a very difficult thing to pin down. Sorry for the aggravation.
 
Dave Martell said:
We're experiencing a problem with posts made under the General category that includes links in the text being sent to the moderation que. It's an intermittent problem though, across different user groups, a very difficult thing to pin down. Sorry for the aggravation.
Click to expand...
No problem Dave; it's not enough to make me bail and go to some other knife forum :viking:
 
Kentucky Jeff said:
Why would you desire flexibilty in a Suji (or any knife)?

I used to think flexibilty was a good quality in a boning/filet knife. Since I started using Japanese knives I no longer think that. The Deba and the Yani are the traditional Japanese Fish knives...no flex there.

There's no knife cut I'm aware of that requires the abilty to flex the blade.

I'm open to other views though...
Click to expand...


I’m able to follow contours (peel an apple with less waste) using a paring knife that has a thin, flexible blade. The ones with better blades are often thicker and stiffer don’t follow curves as well. I also do a better job skinning a fish with a flexible fillet knife cause I’m able to feel the difference between flesh and skin…with a yanagiba, I often cut through the skin without knowing.
 
I have used different types of sujis for all kinds of different tasks. A stiff one has its place and a flexible one does, too. I really prefer thinner and somewhat flexible sujis for almost everything. I had a Hattori FH suji that was stiff and great for portioning ribeyes and things that require a stiffer blade.

I have to again agree with Stephan and say that flexibility is something desirable in a kitchen knife. All of my favorite knives, ie, nenox, konosuke, kikuichimonji, have some flex and some a lot. It makes for a more versatile knife IMO.

As far as sharpening goes, it does take adjustment to really learn how to sharpen a knife that is flexible. I was terrible at it for a while but worked it out. Just takes time and different positioning.
 
Well, I think that a semi flexible suji can be used for more delicate tasks than a robust one. As far as sushi bar work goes, my Konosuke is great for just about everything. I really could get by just using it alone. Everything from filleting fish to getting thin thin slices of avocado. And for general prep, a flexible knife is really good for cleaning out peppers.

Also with suji's as most knives, the thinner the knife is, you tend to have more flex. To me, all of these things go hand in hand with performance. When the Hattori needed to be sharpened, you could feel it big time. The Konosuke, on the other hand would go on for much longer after the edge was dulled simply due to geometry and thinness.
 
I like the little bit of flex that my sujihikis and petty have. Although it mostly just a by-product of the blades thinness, it seems to add to the feeling of nimbleness. Guys who aren't into anorexic knives probably don't view flex as a positive characteristic, I wouldn't think.

Then again, my Takeda kiritsuke has a good amount of flex to it, while my old Takeda gyuto was stiff as a board...and I liked both of them.
 
I think when using the word flex it implies that it will come back to its original shape once released. I will tell you my Takeda 240mm gyuto will bend, and stay bent. I wouldn't call that flex; just strange bendability....
 
It doesn't bother me that my Opinel pocket knife bends instead of flexes, but I wouldn't be crazy about a knife as expensive as a Takesa doing it...
 
It definitely takes longer to sharpen a flexible blade just because you really can't put any force on it without deforming the edge.
 
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