Straightening a Cleaver

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loganrah

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So I just got a new Fujiwara Teruyasu Chinese cleaver and there is a very slight bend in the blade. The bend is what I would describe as parallel to the spine, so the spine and edge are perfectly straight but there is a slight concavity on the right hand side of the knife and slight convexity on the left hand side. It is berely perceptible to the eye but you can just about see the bend if looking down the length from the choil or `tip' end. It is a very small amount, the spine is 3mm at thickest and the bend does not cause the edge to bend `past this' if that makes sense, i.e. the edge is within the boundary defined by thinking of the knife as 3mm thick all over. So the bend cannot be more than a 1.5mm in total over 110mm of height from spine to edge. The knife is san mai with stainless on the outside (don't know what kind) and white #1 on the inside.

The bend is small enough that it doesn't seem to affect cutting performance or cause missed aim (with such a large knife you've got to watch the edge when doing detailed work anyway) However, as I guess most people here are, I'm a little obsessive about this sort of thing and it is annoying me enough to want to try fixing it.

But I have no idea if this is possible or safe to try. My guess would be that the best thing to do would be to get a strong vice, preferable larger than the size of the blade, and simply clamp the knife with some wood on the outside to protect it. Leaving it clamped fairly tight for a reasonable amount of time and perhaps slowly tightening further as/if the bend is decreased?

I'd rather not try anything that requires heating the knife above normal usage temperatures since I'm not confident about my ability to avoid over heating it (and FT heat treat is one of the things that they are praised for so I really don't want to ruin it). The bend is not a bad enough problem to take any serious risk of breaking the knife or reducing the quality of its edge.

Anyway, please share your ideas about whether this is possible to fix, and what might be the best method of doing so with as little risk as possible.

Mods: I figured this fitted better in this forum than the main one but please move it if you think it should go somewhere else.
 

inzite

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So I just got a new Fujiwara Teruyasu Chinese cleaver and there is a very slight bend in the blade. The bend is what I would describe as parallel to the spine, so the spine and edge are perfectly straight but there is a slight concavity on the right hand side of the knife and slight convexity on the left hand side. It is berely perceptible to the eye but you can just about see the bend if looking down the length from the choil or `tip' end. It is a very small amount, the spine is 3mm at thickest and the bend does not cause the edge to bend `past this' if that makes sense, i.e. the edge is within the boundary defined by thinking of the knife as 3mm thick all over. So the bend cannot be more than a 1.5mm in total over 110mm of height from spine to edge. The knife is san mai with stainless on the outside (don't know what kind) and white #1 on the inside.

The bend is small enough that it doesn't seem to affect cutting performance or cause missed aim (with such a large knife you've got to watch the edge when doing detailed work anyway) However, as I guess most people here are, I'm a little obsessive about this sort of thing and it is annoying me enough to want to try fixing it.

But I have no idea if this is possible or safe to try. My guess would be that the best thing to do would be to get a strong vice, preferable larger than the size of the blade, and simply clamp the knife with some wood on the outside to protect it. Leaving it clamped fairly tight for a reasonable amount of time and perhaps slowly tightening further as/if the bend is decreased?

I'd rather not try anything that requires heating the knife above normal usage temperatures since I'm not confident about my ability to avoid over heating it (and FT heat treat is one of the things that they are praised for so I really don't want to ruin it). The bend is not a bad enough problem to take any serious risk of breaking the knife or reducing the quality of its edge.

Anyway, please share your ideas about whether this is possible to fix, and what might be the best method of doing so with as little risk as possible.

Mods: I figured this fitted better in this forum than the main one but please move it if you think it should go somewhere else.
i would suggest raising it as an issue to tf first, very reasonable to deal with imo.
 

malexthekid

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Don't want to question your ability to gauge this, but is it a bend or is it just asymmetric and the edge is off centre?
 

Chicagohawkie

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I can tell you from experience, having had over a half dozen TF knives in the past. There is no perfect TF knive! Most are going to have an issue here and there. Some may be fixable and some not, I always just let it slide for the most part. Also, TF will pretty much ignore you if you have issue, or if you paid via paypal direct from him If you file a grievance he will be forced to respond. If you bought from reseller you can just return, but this sounds like a custom order? It’s hard to tell without seeing a picture to recommend a solution, anyway you can post one?
 

loganrah

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Couple of photos. Sorry about the quality, hard shot to do with a phone camera.

You can see how the ruler touches the knife at the spine and near to the edge but not in the centre.





I'm aware that TFs knives are rustic (to say the least) and I do not consider this to be a concern that warrants a return. The knife's functionality is unaffected and I am otherwise very happy with it. Only a knife collector or obsessive like me would care about or even notice this (I wouldn't have if I hadn't been measuring it for a saya).
 

Chicagohawkie

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Aghhhh. Nice cleaver. In the TF world I would say that falls within acceptable limits. Perhaps some of the knife makers here could provide a suggestion to reverse the bend?
 

inzite

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its not too bad imo, i still think tf would do something about it. TF is pretty good customer service for me so far.
 

chinacats

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I believe that is from grinding on a big round stone (wheel). JMO
 

loganrah

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I believe that is from grinding on a big round stone (wheel). JMO
I couldn't get a good picture of the other side but it has a matching convexity which definitely indicates bending.
 

malexthekid

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It could also just be from tbe forge... damn hard to get a piece of steel that big dead flat with hammer and fire.... is it consistent along the length of the blade?
 

unprofessional_chef

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I'm not recommending you hit the cleaver with a hammer. It's tough to fix if it's in the middle of the blade. Shame the cleaver made it through quality control esp from a Japan knife maker.

[video=youtube;nvhMaYERbT4]https://www.youtube.com/watch?v=nvhMaYERbT4[/video]

[video=youtube;Ot8L2yxW-xQ]https://www.youtube.com/watch?v=Ot8L2yxW-xQ[/video]
 

tripleq

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Very common issue you have there and very easy to fix. Get yourself a non-marring rubber mallet, lay the cleaver (blade) on a flat wooden surface and tap it till it is flat. If you don't have a mallet you can use a regular hammer with a hard rubber bench block or similar to protect the cleaver from the hammer.
 

milkbaby

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If the cutting edge is straight and the cleaver performs well, I personally wouldn't bother doing anything. I'm not sure about san mai since the soft cladding acts differently from the hardened core steel, but hammering on monosteel can also change left to right curvature depending on the stresses in the steel. It's one way of correcting for post-heat treat warp. But with san mai construction, I bet the amount of soft cladding tends to bend and stay bent. The issue that would bother me in trying to correct some things is that you can over correct or cause some other distortion, then you start chasing that and cause another issue, etcetera. Not saying it's not fixable, just to me it wouldn't be worth it and would bother me less than screwing it up more LOL.
 

Drosophil

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There is cosmetic warping and there is warping that affects performance (i.e. when there is a horrible bend in the edge). I have two Munetoshis with spines that look like sine waves near the tip, but the edges are impeccable all the way. They both perform beautifully and are a joy to sharpen.
 

HRC_64

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I'd probably vote to just leave it alone and use it unless it affects performance.

Its seems possible it may induce some kind of steering. Maybe try cutting something that may reveal such a flaw.?

The benefits of finding a cutting flaw is that you have a test to see if you FIX is actually working. Without some kind of testable flaw/fix scenario you are at risk of chasing your tail on the cosmetic stuff and creating more problems, IMHO.

Good luck, either way.
 

loganrah

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I'd probably vote to just leave it alone and use it unless it affects performance.

Its seems possible it may induce some kind of steering. Maybe try cutting something that may reveal such a flaw.?

The benefits of finding a cutting flaw is that you have a test to see if you FIX is actually working. Without some kind of testable flaw/fix scenario you are at risk of chasing your tail on the cosmetic stuff and creating more problems, IMHO.

Good luck, either way.
Thanks everyone, seems like I should probably just leave it alone, definitely don't want to make anything worse.

The only possible performance impact I have detected so far, and I'm not sure about it, was a slight amount of wedging in very thick sweet potato (wedging occurring only when cutting through about a 4 inch diameter piece). This is so minor, and not something I work with very often anyway, that I don't think it really matters. And the knife may well have wedged in a piece that thick and solid without the bend anyway.
 

inzite

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Thanks everyone, seems like I should probably just leave it alone, definitely don't want to make anything worse.

The only possible performance impact I have detected so far, and I'm not sure about it, was a slight amount of wedging in very thick sweet potato (wedging occurring only when cutting through about a 4 inch diameter piece). This is so minor, and not something I work with very often anyway, that I don't think it really matters. And the knife may well have wedged in a piece that thick and solid without the bend anyway.
most likely, 4 inch diameter is pretty beefier, i would imagine 99% of knives wedging or slowing down into a halt.
 

Drosophil

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most likely, 4 inch diameter is pretty beefier, i would imagine 99% of knives wedging or slowing down into a halt.
+1 That happens even with the thinnest of lasers in chunky sweet potatoes
 

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