What is good practise to straighten single bevels?

[natto]

A Tojiro white two 165mm usuba came with a nice and flat ura. Only 2-3cm of the tip bent to the right. The hira is concave from handle to tip, shinogi is a round bevel.

Trying to bend the tip to ura level, the middle of the knife gave in. The Ura became concave. Ups. So far bending works to get out major bends. Two sraightening sticks might help to position the force. No idea wether that might be more precise than the three dovels method.

The only way I know to do precise straightenig, is hammering the concave jigane. Of course this only works in one direction. I would like somthing similar precise to adjust the other direction. So far I am bending the ura to a slight concave and start hammering. Reading the forums there is not much more about straigtening than bending.
Have a look:

You see learnig by doing. A proper hammer and anvil would leave less damage. But I am beyond looks. So far I get the knife reasonable straight. With a more precise technique "to convex" the ura i might get it dead flat.

@JBroida mentioned hammering and chisel hammers. Thank you Jon. Have I missed something in the straightening process?

 

[big D]

If Jon doesn't have anything you can check out Carter, He did a YouTube on straightening with both stick and hammer.

 

[natto]

Thank you. But I didnt find Carter straightening single bevels.

 

[Lurkernomore]

Well, do you have one of these guys?
You can make them yourself as well.

https://item.rakuten.co.jp/sakai-fukui/4941019062176/
Use the rear most slot for bending stuff close to the tip and the diagonal slot for general work around the middle of the blade. Bending this close to the tip sometimes causes the knife to slip out of the stick, so one has to be careful. Yanagiba will lose their tip but usuba are mostly ok even if you do sketchy stuff. The stick needs to be taped up before use, so it doesn’t scratch up the knife.

 

[refcast]

Yayy, someone else who wants to straighten knives!

If you have two pieces of wood or metal, and place them with a space between them, that's how some bends can be be hammered the other way.

It's not absolutely forbidden to hammer on the hard steel. The Kiya Hamono book I had for sale, but ended up donating -- Shigefusa, Iizuka-san, he actually does hammer the hard steel to bend it back for single bevels. The book said he knew it was liable to break though

I myself encountered a similar problem, so I have a bending stick, with another on order. . .

 

[ethompson]

Most important thing with straightening single bevels is to identify a warp (2 axis) vs bend (one axis). A warp typically requires a hammer to tap out. Bending can usually be done with a stick. Just make small adjustments and check often. Recently got into this myself and found practice and patience are the key. A stick with many sized slots is very helpful.

For tapping out, I use funate hammers with the pointy end fully polished out and then tape over the area I’ll be tapping. Seems to help minimize the scarring to some degree.

 

[refcast]

I've been meaning to get a funate hammer, but I have a blacksmith's hammer with a flat face and a peening face (shaped like a "-" sign face).

The worst bends I've seen were on an usuba I had -- that one cracked at the edge from a bending stick. And a chinese cleaver which had warps and bends. . . . man, that one was tough. The choil shot was bent, the spine shot was bent, ugh.

 

[mengwong]

Speaking of usuba defects… what would folks call this? A low spot? The sharpie marks aren’t going anywhere…



Is that what @JBroida was talking about here?

The concave part of the blade road is a function of how the knives are made. Often, they go from a wheel to a buffer and are finished with minimal stone contact, so the low spot in the center of the blade road remains.

 

[ethompson]

Yeah, that’s a low spot. Not so much a defect as just a product of how they’re ground on big wheels. Will come out over time.

 

[natto]

Speaking of usuba defects… what would folks call this? A low spot? The sharpie marks aren’t going anywhere…

Is your knife bent? How is the ura at the lows pot?

 

[natto]

Yayy, someone else who wants to straighten knives!

If you have two pieces of wood or metal, and place them with a space between them, that's how some bends can be be hammered the other way.

I'll check how precise I can do that. Got a warped piece of wood which might do it. This way I could avoid to hammer the hagane.

It's not absolutely forbidden to hammer on the hard steel. The Kiya Hamono book I had for sale, but ended up donating -- Shigefusa, Iizuka-san, he actually does hammer the hard steel to bend it back for single bevels. The book said he knew it was liable to break though

Is this about hammering the concave to convex with light taps? Or is this about using a hammer with more weight, to bend a convex to concave, like above?

So far I am hammering the concave jigane with the small side of the hammer and repeated light taps. Works precise like a charm. A large hammer lying on my lap as anvil. And this is how I got this ugly hammer marks. Its not easy to place the knife at the sweet spot in the right angle and hammer precise.

 

[Blank Blades.]

Hmmm.

 

[deltaplex]

You can use a punch (nail punch) and a hammer as well, I've found that to be more precise than using the peen side, and I've had success with just some sheet steel stacked as a stand in for the anvil. I don't know what you've got lying around, but those would be a pretty big improvement over the peen and extra hammer you have been doing.

 

[natto]

Most important thing with straightening single bevels is to identify a warp (2 axis) vs bend (one axis). A warp typically requires a hammer to tap out. Bending can usually be done with a stick. Just make small adjustments and check often. Recently got into this myself and found practice and patience are the key. A stick with many sized slots is very helpful.

For tapping out, I use funate hammers with the pointy end fully polished out and then tape over the area I’ll be tapping. Seems to help minimize the scarring to some degree.

Good point. What is the diameter of the pointy end, and which weight do use?

 

[natto]

You can use a punch (nail punch) and a hammer as well, I've found that to be more precise than using the peen side, and I've had success with just some sheet steel stacked as a stand in for the anvil. I don't know what you've got lying around, but those would be a pretty big improvement over the peen and extra hammer you have been doing.

More precise is music in my ears. I would like to make a punch nail with a handle, some different straightening hammers. What should the shape of the tip look like?

My hammer used as anvil is about 2000g. At the moment I am thinking of how to mount the hammer at a convenient height. The ura touches the convex hammer face. Hitting that point moves metal.

Stacking steel sheets is funny. Got two sheets left, about 3 to 4mm wide, put on brick. A short try feels different than a solid mass backing the hammer blow. But a worn nail punch freehand left some marks. The knife staying put is definitely an improvement

 

[ethompson]

Good point. What is the diameter of the pointy end, and which weight do use?

I have two that I use for this. The first is very light, about 175g with a 3-5mm head on he pointed side. The second is larger, about 750g with a 8-10mm point

 

[deltaplex]

More precise is music in my ears. I would like to make a punch nail with a handle, some different straightening hammers. What should the shape of the tip look like?

My hammer used as anvil is about 2000g. At the moment I am thinking of how to mount the hammer at a convenient height. The ura touches the convex hammer face. Hitting that point moves metal.

Stacking steel sheets is funny. Got two sheets left, about 3 to 4mm wide, put on brick. A short try feels different than a solid mass backing the hammer blow. But a worn nail punch freehand left some marks. The knife staying put is definitely an improvement

I think the one I use for it is ~ 3-4mm in diameter. I may have a larger diameter one in my great grandfather's tool chest, but I haven't needed one larger than the 3-4 mm one. I think I stacked 4 sheets of 1/4" on my portable workbench last time as the base, but if you find that the 2 Kg hammer face gives better "spring" (or however you want to describe it's effect) then I'd probably just clamp it/vice it in place.

 

[ethompson]

https://www.bladeforums.com/threads/straightening-hammer-jts-design.1729208/post-19756986
You don't need an anvil by the way. Here is a link to Harbeer, @HSC /// Knives , demonstrating straightening on a stump. The video I've seen of Carter using a chisel hammer to do the same was also on a stump.

 

[natto]

There are some different ways working. I need some time to check.

Thank you

 

[mengwong]

Is your knife bent? How is the ura at the lows pot?

The uraoshi narrows at a point that’s offset from the low spot. It’s probably fine. Just to the left of the dark part of the reflection.



(Just spent an hour on 220 and another hour through to 8k… turns out people in the household looking to chop supplement tablets in half will unerringly choose the Usuba. So now I have a convex edge



Sorry to fork the thread, everyone.

 

[natto]

The uraoshi narrows at a point that’s offset from the low spot. It’s probably fine.

Uneven bevels like on your first picture can indicacte warps and bends. I thought of checking geometry and straightening if needed. But after grinding the ura flat, there is not much room left for further straightening.

The wide grinding marks indicate convexity ground off. Small indicates concavity, barely touched. The wide mark at the spine might correspond to the low spot at the bevel.

JBroida's comment was about a slight concave left on the bevel. That should be similar concave from heel to tip. But that is from grinding wheels, not related to bends.