# Blade Flex and Sujis



## mr drinky (May 8, 2011)

I was just reading Stephan Fowler's thread on his new suji (which looks awesome), but there was a comment in there about the (desired) flexibility of suji blades. I didn't want to pollute that thread, so here is my question.

I don't have a suji but will be looking for one come fall, so what are the advantages of one with more flex versus less flex?

For some reason, I have Hung's video in my head where he uses a Misono UX10 suji for a cutting demonstration. Right at the beginning he shows how flexible the blade is by pressing it on the counter. Because of this, I have always thought of sujis as more flexible. Video below.

http://www.youtube.com/watch?v=xwciXwM_5FA

So basically, I am suji ignorant. Anybody have some buying tips?

With that said, in the end I may just go for one of Pierre's or Butch's knives. 

k.


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## Dave Martell (May 9, 2011)

Thin ground knives that are not tall in height and long in length will flex easily, the idea is to not have so much flex that they go where they want, you want them to go where you aim them.


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## Lefty (May 9, 2011)

mr drinky said:


> I was just reading Stephan Fowler's thread on his new suji (which looks awesome), but there was a comment in there about the (desired) flexibility of suji blades. I didn't want to pollute that thread, so here is my question.
> 
> I don't have a suji but will be looking for one come fall, so what are the advantages of one with more flex versus less flex?
> 
> ...


 
I love that video and I know the exact part of it that you are talking about!
When you watch, you can tell he is pushing pretty hard, but Misono stainless (in my experience) can be pretty flexi. I like how my moly gyuto feels because of it's little bit of play and very light feel.
I'll be looking at a 270 suji in the future, and I imagine the flex is far less of a problem than it is with a 300. 
You should ask wildboar how much flex is in his 270 (I believe) suji to see if whipiness is an issue (I doubt it is).


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## tk59 (May 9, 2011)

If the knife is a dedicated slicer, there isn't an advantage for the blade to be particularly thin. For an all-arounder, a bit thinner makes it a lot more friendly, imo. How thin depends on what you're cutting, I suppose but I'd say that as long as the tip area is quite thin, it will perform well. Knives that are very thin near the heel feel odd going through heavy, harder objects.


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## Salty dog (May 9, 2011)

I own two very high end 270 sujis. Watanabe and Masamoto. Niether are very flexible. A little near the tip.


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## Lefty (May 9, 2011)

Salty, do you have a 300 suji? If so, isn't it much more flexible than your 270s?
I just can't recall anyone complainin about a 270 being too whippy, that's all.


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## Salty dog (May 9, 2011)

No 300 sujis.


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## Lefty (May 9, 2011)

Gotcha!
I sure won't ever need a 300, but then again, I'm not a chef.


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## Cadillac J (May 9, 2011)

I've never had any flex issues with my 270(2) or 300 sujis. They might have a little give to them near the tip like Salty said, but I've never had a blade not go where I want in a cut because of this at all.


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## StephanFowler (May 9, 2011)

mr drinky said:


> I was just reading Stephan Fowler's thread on his new suji (which looks awesome), but there was a comment in there about the (desired) flexibility of suji blades. I didn't want to pollute that thread, so here is my question.
> 
> I don't have a suji but will be looking for one come fall, so what are the advantages of one with more flex versus less flex?
> 
> ...


 
I may have given the wrong impression, the blade in that thread is not dead stiff, I can grab the tip with my fingers and flex it a good inch out of straight pretty easily, it's clearly not as flexy as the knife in that video but it will flex if asked. 

it's just designed to be "less" flexy if that makes any sense

Stephan


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## WildBoar (May 9, 2011)

Lefty said:


> You should ask wildboar how much flex is in his 270 (I believe) suji to see if whipiness is an issue (I doubt it is).





StephanFowler said:


> I may have given the wrong impression, the blade in that thread is not dead stiff, I can grab the tip with my fingers and flex it a good inch out of straight pretty easily, it's clearly not as flexy as the knife in that video but it will flex if asked.
> 
> it's just designed to be "less" flexy if that makes any sense
> 
> Stephan


My suji is a 300. I can 'flex' the blade laterally ~ one inch if I push on it hard enough. This has never been an issue while carving, although it's possible it moves a little around bones and I just have not noticed. Frankly until I read this thread, I had not even been curious about it.


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## Lefty (May 9, 2011)

Sounds like it is NOT a problem then


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## NO ChoP! (May 9, 2011)

I have a 300...(Moritaka) zero flex. Yet my 240 does have a little flex.... (I find flex is only good if your going to filet with it)

It seems that when going from a 270 to a 300, it isn't just an extra 30mm added. The entire profile/ geo changes. See Caddy's recent postings comparing his 300 w2 to his new 270 HD. The 300 casts a shadow on the 270.... I found it very interesting.


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## tk59 (May 9, 2011)

Actually, I wonder how much the steel and the HT have to do with flexibility. I recently looked at several laser-types and some flexed a LOT more than others even though the thickness was very similar.

No Chop, I was gonna say that I didn't think Cadillac has a W2 blade but then I realized you meant Hitachi White 2. I was totally shocked at the gyuto-ness of the 300.


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## Kyle (May 9, 2011)

I recently sold my Konosuke 270mm suji because it was too flexy for my needs. I'm still using a 300mm Kanemasa suji as a dedicated BBQ/brisket slicer.


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## Salty dog (May 9, 2011)

Yeah, you don't need much flex with a bbq slicer. I used to do it professionally. Believe it or not a big yanagi works pretty good.


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## mr drinky (May 9, 2011)

tk59 said:


> If the knife is a dedicated slicer, there isn't an advantage for the blade to be particularly thin. For an all-arounder, a bit thinner makes it a lot more friendly, imo. How thin depends on what you're cutting, I suppose but I'd say that as long as the tip area is quite thin, it will perform well. Knives that are very thin near the heel feel odd going through heavy, harder objects.


 
This was sort of what I was thinking. A thinner more flexible one might be a better all-around knife (as long as the flex isn't too much that is), but I would mostly have the knife as a dedicated slicer anyhow. I think I would go with something stiffer. I have a 7.5" Forschner utility knife that is quite flexible and use that when I need some added maneuverability around bones. A dedicated boning knife might be in order at the same time. Maybe Dave will even have his butcher set going by then. 

Btw, did I hear that Misono knives are stamped, or am I wrong on this? I know they run a bit on the softer side at 59 HRC, but do stamped blades allow for more lateral flex? Just a thought. 

k.


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## tk59 (May 9, 2011)

Yes, Misono are not forged. They aren't simply stamped like Forschners are, either. They do taper in both directions. As for the flexibility, I don't know if forging makes a difference...


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## wenus2 (May 9, 2011)

My 300 Harner gives about 1/2" or so at the tip is all, it's perfect for my needs.



tk59 said:


> I was totally shocked at the gyuto-ness of the 300.


I'm with you, when my Butchihiki arrived (after I got over the initial shock of it's beauty) I took a double take for that same reason. I went over and grabbed out my 210 Kono gyuto and sure enough, they matched up almost perfectly for the first several inches. It makes for a great all-arounder if you have room to work the big bastard :chefcut:


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## Cadillac J (May 9, 2011)

wenus2 said:


> My 300 [...] makes for a great all-arounder if you have room to work the big bastard



Hell yeah man. 

Even with how much I'm enjoying my new 270, I still like to grab my 300 now and then. I don't think I'll ever be able to let it go (hopefully, as I've said this many times before...so we'll see in the next year) 
:moonwalk:


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## Lefty (May 9, 2011)

I'm wondering what the real advantage of a 300 over a 270 would be in a home setting. My 240 gyutos provide all the length I need. I know a longer blade allows for a less disturbed/cleaner slice, but so does being careful and knowing where your edge is. Maybe portioning steaks and trimming out roasts with a utility and a short scimitar taught me to be patient and precise.
Is there anywhere that a 300 will really be better than a 270?


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## Kyle (May 9, 2011)

Personally, when I'm slicing large briskets I prefer a long slicer. The 270 wasn't quite right for me.


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## tk59 (May 9, 2011)

I certainly don't need a 300 but if I'm slicing something with a tough exterior, sometimes it takes quite a bit of draw before you get through it. Plus, it's an advantage to be cool, isn't it?


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## WildBoar (May 9, 2011)

My 300 has been good for carving pork roasts (shoulders) and rib roasts. Glad I went with 300 vs 270. Part of me is sad I didn't go for 330! :smile1:


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## Lefty (May 9, 2011)

tk59 said:


> I certainly don't need a 300 but if I'm slicing something with a tough exterior, sometimes it takes quite a bit of draw before you get through it. Plus, it's an advantage to be cool, isn't it?


 
Now I get it! Haha


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## Delbert Ealy (May 11, 2011)

tk59 said:


> Actually, I wonder how much the steel and the HT have to do with flexibility. I recently looked at several laser-types and some flexed a LOT more than others even though the thickness was very similar.
> 
> No Chop, I was gonna say that I didn't think Cadillac has a W2 blade but then I realized you meant Hitachi White 2. I was totally shocked at the gyuto-ness of the 300.




I was talking about this very subject today, and flex has to do with the geometry of the blade, the steel and the heat treat mean almost nothing when it comes to flex. Its all about the geometry, having said that with flex a very small change in the geometry say .1mm or less can produce huge chages in the flex. Flex is not affected by forging either.
Del


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## PierreRodrigue (May 11, 2011)

+1 In the fillet knives I do, some guys want very flexible, some like medium, and some stiff. Essentially, the only difference in the knife is the geometry of the grind, I use the same starting stock, and the HT is the same. Final hardness is within 1 point. You can really affect the flex, with minimal change to the geometry.


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## StephanFowler (May 11, 2011)

Delbert Ealy said:


> I was talking about this very subject today, and flex has to do with the geometry of the blade, the steel and the heat treat mean almost nothing when it comes to flex. Its all about the geometry, having said that with flex a very small change in the geometry say .1mm or less can produce huge chages in the flex. Flex is not affected by forging either.
> Del


 
yep, I had a long long conversation with Kevin Cashen at a hammer in once about the modulus of elasticity and he proposed an "experiment"

I took several bars of 1/8 x 1" 1084 and clamped them horizontal off of a table with 12" hanging off the table. 

one bar was not modified at all, one bar was given a very thorough anneal, one bar was heat treated in oil, one was heat treated in water

a 50Lb weight hung off the end of the bar produced the exact same amount of flex in each and every bar.

so I re did the test, using 5 samples all ht'd together and tempered to the same hardness
one, piece was left in it's original shape, one piece was given a distal taper, one was beveled, one was beveled and tapered, and the last was convex beveled and tapered.

all of them flexed differently - again, the only measurable difference between the 5 samples was the grind


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## WildBoar (May 11, 2011)

Modulus of elasticity (steel property), moment of inertia (i.e., cross-section) and blade length dictate amount of deflection for a given load:

http://www.engineersedge.com/beam_bending/beam_bending9.htm

Haha, don't get to use my structural engineering skilz very often on the knife forums


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## WildBoar (May 11, 2011)

uh oh -- previous post needs moderator approval. I'm guessing theat's due to the link


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## tk59 (May 11, 2011)

WildBoar said:


> uh oh -- previous post needs moderator approval. I'm guessing theat's due to the link


 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!


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## WildBoar (May 11, 2011)

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!


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 :-(


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## tk59 (May 11, 2011)

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 :-(


 
Interesting. I wonder what sorts of posts need Mod approval... Is there a place to look that up?


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## Kentucky Jeff (May 11, 2011)

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...


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## WildBoar (May 11, 2011)

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.


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## mr drinky (May 11, 2011)

Thanks everyone for your experience. I love it when I learn way more than I thought I was going to learn.

k.


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## WildBoar (May 11, 2011)

tk59 said:


> Interesting. I wonder what sorts of posts need Mod approval... Is there a place to look that up?


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


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## mr drinky (May 11, 2011)

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.


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## tk59 (May 11, 2011)

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.
> 
> ...



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.


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## NO ChoP! (May 11, 2011)

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...


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## StephanFowler (May 11, 2011)

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.
> 
> ...


 

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.


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## mhlee (May 11, 2011)

StephanFowler said:


> It's more of the case of accepting flex as a byproduct of another trait that is more important than stiffness.



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.


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## Dave Martell (May 11, 2011)

tk59 said:


> Interesting. I wonder what sorts of posts need Mod approval... Is there a place to look that up?




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.


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## WildBoar (May 11, 2011)

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.


No problem Dave; it's not enough to make me bail and go to some other knife forum :viking:


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## festally (May 11, 2011)

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.
> 
> ...




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.


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## Mattias504 (May 11, 2011)

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.


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## tk59 (May 12, 2011)

Mattias504 said:


> ...It makes for a more versatile knife...


 How so?


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## Mattias504 (May 12, 2011)

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.


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## Cadillac J (May 12, 2011)

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.


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## NO ChoP! (May 12, 2011)

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....


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## EdipisReks (May 12, 2011)

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...


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## tk59 (May 13, 2011)

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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## EdipisReks (May 13, 2011)

tk59 said:


> It definitely takes longer to sharpen a flexible blade just because you really can't put any force on it without deforming the edge.


 
oh, for sure.


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