Have you straightened knives before?

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What straightening work have you done before?

  • Straightened double bevel clad knives

    Votes: 40 83.3%

  • Straightened single bevels

    Votes: 18 37.5%

  • Straightened deba

    Votes: 10 20.8%

  • Performed uradashi for edge contact

    Votes: 11 22.9%

  • Removed twists

    Votes: 17 35.4%

  • Straightened honyaki or hard monosteel

    Votes: 12 25.0%

  • Ground an new ura

    Votes: 7 14.6%

  • Checked the edge and spine for straightness

    Votes: 43 89.6%

  • Checked the geometry for consistency and asymmetry

    Votes: 42 87.5%

  • Cracked blades or broke them

    Votes: 18 37.5%
  • Total voters
    48
R

refcast

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Since I've bought secondhand knives from Japan, I've been regularly straightening and making basic knife repairs. I wondered who else has had experience looking for edge and spine straightness, and geometry consistency, whether makers, hobbyists or users.

For me, straightening deba is really hard. Haven't done hard monosteel yet -- only 60hrc monosteel via chisel hammer, and a honyaki soft tang, but not the hard steel itself or soft steel above the hamon.

I've cracked an usuba edge, a tf gyuto edge, an ajikiri in the blade hollow, snapped a couple deba tip off, snapped a yanagi tip off.

I can kinda tell when steels aren't tempered enough and can't take bending or hammering now haha.

How do you guys remove twists? I've been using a carbide chisel hammer for that in double bevels and single bevels.

This is a follow up from some Japan proxy questions I had been trying to answer. Which is, yeah knives can be cheaper from the auction, but they can be malformed or unusable in odd, odd ways that take awhile to fix, or not if the knife somehow is good, which is very rare in my purchases

I try to check edge recurves too, I have a flat plate for that as well as ura contact and straightness of the edge from heel to tip. I do it by eye now, looking at the knife from the tip, moving it left to right
 
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I hope this thread grows, it'll be a valuable learning resource for anyone doing long term maintenance on their knives.

I had to trial and error through so many low spots, high spots, edge warps, bad grinds, accordion edges, the horror of it all.
 
More_Gyutos said:
That’s really interesting, care to share the maker?
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Yanick - haven’t had multiple new examples from Milan sadly but with as much stone work as he puts in I have a hard time seeing them coming less than straight. Clad knives move over time, that’s just part of it, not a flaw. Though I’ve gotten many knives with enough bend to be called a flaw. Only would be an issue mostly after repeat sharpenings, when thinning is needed, or for polishing.
 
Isn’t uradashi a woodworking tool thing? Plane geometry is beefy and forgiving, I don’t see it working on a knife tbh.
 
Lurkernomore said:
Isn’t uradashi a woodworking tool thing? Plane geometry is beefy and forgiving, I don’t see it working on a knife tbh.
Click to expand...
Works pretty well on single-bevels and I’ve used it on low bevels too. Would be my first way to “correct” this as I don’t think it’s coming out with a bending stick given the size and location. And I wouldn’t really call it uradashi, but there is more info out there on uradashi and the process is pretty similar in theory. Metate hammers and the general principles applied to saw straightening are also useful for thin knives.
 
You might be surprised just how little force is needed to hammer a knife straight... Don't be (overly) scared, get your cold forging on and get that edge straight!

Hammering is much preferable to a stick for propeller twists too
 
A propeller twist I’d address with a chisel I guess, though I haven’t yet done it. I only use sticks so I can’t fix warp.
About the uradashi thing: assuming a bevel without low spots and a low spot in the urasuki, wouldn’t hammering down the bevel to make contact create a low spot in the bevel? Then when you grind out the low spot on the bevel you lose blade height and again grind into the low spot on the back which is still there. What I’m saying is that it seems to me that it’s only a very temporary fix and only regrinding the back would fix the actual root issue.
 
Lurkernomore said:
A propeller twist I’d address with a chisel I guess, though I haven’t yet done it. I only use sticks so I can’t fix warp.
About the uradashi thing: assuming a bevel without low spots and a low spot in the urasuki, wouldn’t hammering down the bevel to make contact create a low spot in the bevel? Then when you grind out the low spot on the bevel you lose blade height and again grind into the low spot on the back which is still there. What I’m saying is that it seems to me that it’s only a very temporary fix and only regrinding the back would fix the actual root issue.
Click to expand...
If by low spot you mean overgrind, then yes, tapping for edge contact or straightness is a temporary fix and doesn’t resolve the root problem long term. I’m not claiming you can fix an overgrind with a hammer. But you must definitely can correct small bends, warps, twists with a hammer. This specifically seems to be a low spot on one side with a matching high spot on the other side and slight wave to the edge. A great candidate for this treatment rather than feverishly grinding away at a high spot on one side and a low spot on the other side.
 
ethompson said:
If by low spot you mean overgrind, then yes, tapping for edge contact or straightness is a temporary fix and doesn’t resolve the root problem long term. I’m not claiming you can fix an overgrind with a hammer. But you must definitely can correct small bends, warps, twists with a hammer. This specifically seems to be a low spot on one side with a matching high spot on the other side and slight wave to the edge. A great candidate for this treatment rather than feverishly grinding away at a high spot on one side and a low spot on the other side.
Click to expand...
I’ll also add that if I had a choice between an ura that makes full clean contact and having to correct with additional hammering overtime vs trying to regrind an ura that was overground, butting a bevel on the ura side, or having an ura that couldn’t be contacted I’ll take the effort of using hammering to create a functional knife each time. But agree, it’s a bandaid not a solution.
 
refcast said:
Since I've bought secondhand knives from Japan, I've been regularly straightening and making basic knife repairs. I wondered who else has had experience looking for edge and spine straightness, and geometry consistency, whether makers, hobbyists or users.

For me, straightening deba is really hard. Haven't done hard monosteel yet -- only 60hrc monosteel via chisel hammer, and a honyaki soft tang, but not the hard steel itself or soft steel above the hamon.

I've cracked an usuba edge, a tf gyuto edge, an ajikiri in the blade hollow, snapped a couple deba tip off, snapped a yanagi tip off.

I can kinda tell when steels aren't tempered enough and can't take bending or hammering now haha.

How do you guys remove twists? I've been using a carbide chisel hammer for that in double bevels and single bevels.

This is a follow up from some Japan proxy questions I had been trying to answer. Which is, yeah knives can be cheaper from the auction, but they can be malformed or unusable in odd, odd ways that take awhile to fix, or not if the knife somehow is good, which is very rare in my purchases

I try to check edge recurves too, I have a flat plate for that as well as ura contact and straightness of the edge from heel to tip. I do it by eye now, looking at the knife from the tip, moving it left to right
Click to expand...
Exactly what carbide chisel hammer are you using? I’ve been looking for one.

Straightening knives is a slightly nerve wrecking exercise for me. A mix of fear I’m gonna break the knife and having a hard time seeing if it’s actually warped / twisted or straight already.
 
Lurkernomore said:
A propeller twist I’d address with a chisel I guess, though I haven’t yet done it. I only use sticks so I can’t fix warp.
About the uradashi thing: assuming a bevel without low spots and a low spot in the urasuki, wouldn’t hammering down the bevel to make contact create a low spot in the bevel? Then when you grind out the low spot on the bevel you lose blade height and again grind into the low spot on the back which is still there. What I’m saying is that it seems to me that it’s only a very temporary fix and only regrinding the back would fix the actual root issue.
Click to expand...

I was trying to think of how to explain it, but many single bevel knives have convexing and a microbevel. So even if make a low spot in that place, or hammer marks, I have convexing I can thin to remove the marks, or even the grind again. Grinding uraoshi again on a waterwheel -- I don't have a water wheel, so it's simply because it's not practical for me to address the ura work that way, or with small coarse stones. Removing more hard steel makes the knife more prone to bends, too, so I keep that in mind. Hammering goes together with water wheels in forming the urasuki an even uraoshi. The splitting action of the carbide chisel hammer is kind of hard to explain, but like how an axe wedges in wood and splits the wood apart, the chisel hsmmer splits iron or steel apart at the surface, and forces the rest of the knife to move in those directions.
 
@Genghis_F

Shindo is a thin clad knife, a peen hammer and two pieces of wood should work. Space the pieces of wood to accommodate the hammer blow and movement of the knife. I'll draw something up. But a twist is like a diagonal bend. Hammer not near the edge but on the blade face -- hammer blows near thin edges can tear them like paper lol.

Carbide hammer totally works too. Different mechanism of unbending though. The regular hammer and carbide hammer will have the knife facing different sides to work. Carbide hammer -- the knife should look like a valley, the carbide chisel will split the surface iron apart and spread it, like a thick knife pushes food apart. Regular hammer -- knife should look like a hill to pound down, areas immediately next to the twist are supported by wood, under it is the gap between the pieces of wood. Wood are similar height.

But carefully check progress as you go -- hammers, or copper hammers, or so on those marr the blade face less
 
refcast said:
@Genghis_F

Shindo is a thin clad knife, a peen hammer and two pieces of wood should work. Space the pieces of wood to accommodate the hammer blow and movement of the knife. I'll draw something up. But a twist is like a diagonal bend. Hammer not near the edge but on the blade face -- hammer blows near thin edges can tear them like paper lol.

Carbide hammer totally works too. Different mechanism of unbending though. The regular hammer and carbide hammer will have the knife facing different sides to work. Carbide hammer -- the knife should look like a valley, the carbide chisel will split the surface iron apart and spread it, like a thick knife pushes food apart. Regular hammer -- knife should look like a hill to pound down, areas immediately next to the twist are supported by wood, under it is the gap between the pieces of wood. Wood are similar height.

But carefully check progress as you go -- hammers, or copper hammers, or so on those marr the blade face less
Click to expand...
Thanks!
Sounds like regular hammer may be more forgiving of a noob
 
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