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Repairing Kitchen Knives

Below is copied a post I just did on KKF outlining how to repair kitchen knives. The basics of the method are largely the same whether you're dealing with chipping, tipping, or restoring the profile of a knife that has been over-sharpened in some way (usually the result of bad use of a honing rod or steel).

If you're a pro you can do this kind of thing with belts, but hopefully I'm going to show it's not to tricky to do on stones either. So hopefully might be helpful for anyone who hasn't done it before.

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This is a knife someone bought from me a while back, and sometime later their better half (allegedly) tried to use it to break down a chicken. Which tends not to sit very well with thin Japanese grinds and hard Hitatchi steels.

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That's some pretty gnarly chipping. It's gone pretty much up to the beginning of the core steel and we're going to lose both some height and length in sorting it.

First things first is to visualise what you want to do. Sketch the outline of the knife on a piece of paper so you can draw on top how you might want the finished profile to look. I usually prefer to lose more length from a knife than height, as it'll require less significant thinning and rectifying of the geometry afterwards, but you'll need to do a bit of both and where you draw those lines is up to you. Note that if you're repairing a knife that has been 'tipped' you can (and should probably) remove at least some of the material from the spine of the knife in order to try to match the original profile.

TBH I don't always do a sketch like this, but it takes no time at all and is very useful to compare against as you work, so might as well.

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Now let's think about stones. As you can see from the previous picture - I'm going to have to remove a considerable amount of hardened steel just to repair the profile of the knife, before I even get to thinning the main bevel, so I'm going to need something pretty coarse. Vitrified Silicon Carbide or Aluminium Oxide stones are your friend here, the kind of thing that gets sold by Norton under the brand names Crystolon and India. These stones do not dish readily, they cut fast, and we're going to be using a lot of pressure and probably a relatively high angle. You could use a low-grit waterstone but a vitrified stone will smoke them for speed, won't wear the stone excessively and you'll be less likely to dig in. Plus they're very cheap and usually come as Coarse and Fine combis which is going to be handy, the JIS equivalent of a SiC Coarse and Fine might be something like 140 and 320 Grit.

That's the only stone I'd really recommend something particular, after that you can get creative. We're going to need to do some considerable thinning of the knife, so if possible trying to use as many coarser stones as you have early on is a good idea for removing scratch patterns. I don't have mine with me atm but something like a Shapton Glass 500, which also isn't very dishy, would be a great stone to jump to after the SiC / AlOx, and then begin whatever kind of sharpening / polishing progression you want. I don't have any of my normal polishing stones with me either so I'm getting a bit creative here, we'll see how it pans out (I'm writing this as I go along).

L to R: Norton India Coarse and Fine, Washita, Turkish Oilstone, Gwespyr, Moughton Whetstone, Glanrafon, Blue Tam O'Shanter. A rainbow selection!

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So there are a couple ways to skin this cat... You could 'breadknife' it; sawing into the stone at 90 degrees with pressure to remove the chips until you've got the profile matching the sketch you did, and then start on thinning. Or you can 'sharpen' it into shape, with the knife at an angle, and using a more normal sharpening motion. I tend to prefer the latter as it's a slightly more delicate operation though I don't do it at the kind of angle you'd normally sharpen at, more like 45 degrees. This makes it quicker to get the chips removed, but still means you'll need to do some thinning after though not as much as if you 'bread-knifed', you can pick wherever along the angle spectrum you want. You could, I suppose, do the thinning simultaneously; with a 'zero-bevel' - laid flat against the stone - and then build the edge and convexity in after, but it strikes me as a slightly odd way of doing repair work.

After about 10 mins with reasonable pressure I've got here.

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And obviously you can check it against your sketch as you're working. I didn't in this instance because I've done this kind of thing a bit before, so it was nice to see at the end that I'm pretty much spot on, and not actually lost a huge amount of length. You can see how the 'shinogi' line where the main bevel starts has been moved up in accordance with where we've removed metal at the edge - particularly toward the tip of the knife. This allows you maintain proper geometry of the main bevel when thinning. On a 'Tosa' style knife like this it might not be aesthetically ideal because you start revealing some hammer forging marks, but if people are going to smack their knives through chicken bones and then send to me to repair, they will get what they're given!*

From here it's basically just thinning, resetting the edge, and polishing if you want, and this part will take considerably longer to do well. Just to be clear - 'thinning' is kinda like sharpening but at a more acute angle than you would sharpen the edge of the knife at - you're basically rebuilding the main bevel of the knife. The easiest way do do it initially is to have the bevel laid flat against the stone, applying pressure just below the shinogi line for the majority of the thinning. And then toward the end gradually moving the pressure down toward the edge to get convexity if you want it. At least that's how I do it but it's kind of self-taught, there are probably a load of other ways, so anybody else please chime in with thoughts or other suggestions.

For most of it I'm using the fine side of the Norton India because the scratches will be shallower than the coarse side, and then the Washista. It's ideal to have quite a hard stone(s) here, as they don't dish and allow more precision and control. If I wasn't concerned about the look of the knife afterwards then I could do the whole repair, thinning and sharpening on these two stones. But I'm going to use a Turkish after; because they're quite friable with a bit of practice they can actually be fantastic polishing stones, removing scratches from previous leaving a completely even haze on the cladding. It's pretty messy though! Before going onto an all-British polishing and sharpening progression. As I said above, normally I might do something like Shapton Glass 500, King 800, King 1200, then a couple of Jnats. Pick your own fun!

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And here's the end result... I'm not massively thrilled with the polish tbh, and I'm going to blame my tools for that; I could've done with a King stone to get some early scratches out, and these stones are probably a little too hard to do convex polishing particularly easily (that's a guess - I don't do much convex polishing generally, so tbh probably as much my own shortcomings). I might try going over it again before giving back if I'm bored at some point.

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I am quite happy with the profile and geometry though; I've got some nice convexity which gradates nicely from being thicker at the heel, as you can see from my cr*ppy effort at a choil shot, to pretty thin at the tip. And hopefully will make it a bit more robust so this kind of thing is less likely to happen in the future.

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I put the final edge on with the Tam O'Shanter, which is a superb knife sharpening stone when used with mud, somewhere around 6k, but with lots of bite and teeth. Goes through carrots like a champ, and effortlessly through a napkin.

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And a final lick of oil on the handle, as it is I think one of my nicer ones:

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* TBF it actually belongs to the brother of a good friend, and I'm doing it for free. He was going to take it to one of those mobile sharpening people, who 9 times in 10 will completely f*** up something like this by trying to do it all on belts in 45 seconds flat. So I basically insisted he send to me instead.

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As I say - there are many options in the cat-skinning game, that's just how I do it. And it seems to work for me, so hopefully someone else might find it useful.
 

OldSaw

The wife's investment
Thanks for sharing. Your posts and PM’s have really helped me to improve my knife sharpening game. I even bought a piece of crap paring knife for my wife yesterday because hers went missing and I felt confident that I could make it work. (Plus I didn’t want her using my good ones.)
 
Thanks for sharing. Your posts and PM’s have really helped me to improve my knife sharpening game. I even bought a piece of crap paring knife for my wife yesterday because hers went missing and I felt confident that I could make it work. (Plus I didn’t want her using my good ones.)


Ah cheers! Always nice to hear when my (somewhat niche) area of expertise is helpful for others :).
 
I'm going to attempt a similar repair this week! Smaller chips, and I'm not going to try to redo the tip, but it'll still be a good project!

Biggest chip & its neighbors:
IMG_20220322_193047568.jpg


Broken tip:
IMG_20220322_193119143.jpg


I got it sharp enough with the chips, and the owner clearly doesn't care, but I want to at least try to sharpen them out.

King 300 is arriving Thursday :)
 
I'm going to attempt a similar repair this week! Smaller chips, and I'm not going to try to redo the tip, but it'll still be a good project!

Biggest chip & its neighbors:
View attachment 1428013

Broken tip:
View attachment 1428014

I got it sharp enough with the chips, and the owner clearly doesn't care, but I want to at least try to sharpen them out.

King 300 is arriving Thursday :)
For tip repair you can remove some metal off the spine of the tip. It will change the profile of the edge less. If the spine was rounded out and polished it can take some elbow grease to get it looking like it was. Most people don't care about that as much. They just want a tip. Good luck with it!
 
The stone arrived early!

Here are some after shots:

IMG_20220323_192736916.jpg


IMG_20220323_192744183.jpg


I obviously didn't repair the tip. It's still not perfect, but it is in much better shape than when I started!

I have until Sunday; I may give it another go. There's one tiiiiiiiny chip that I can't see, but I feel it with my fingernail. I know that'll come out easily enough.

@cotedupy outlining and sketching a plan before the repair was a really helpful idea, thanks for that!

@ChefJohnBoy-ardee I'm still not ready to try tip repair. The spine idea is a pretty good one though. I may ask to borrow this knife again down the line and try it.
 

FarmerTan

"Self appointed king of Arkoland"
The stone arrived early!

Here are some after shots:

View attachment 1428483

View attachment 1428485

I obviously didn't repair the tip. It's still not perfect, but it is in much better shape than when I started!

I have until Sunday; I may give it another go. There's one tiiiiiiiny chip that I can't see, but I feel it with my fingernail. I know that'll come out easily enough.

@cotedupy outlining and sketching a plan before the repair was a really helpful idea, thanks for that!

@ChefJohnBoy-ardee I'm still not ready to try tip repair. The spine idea is a pretty good one though. I may ask to borrow this knife again down the line and try it.
The difference is already amazing my friend. Good work!
 
For tip repair you can remove some metal off the spine of the tip. It will change the profile of the edge less. If the spine was rounded out and polished it can take some elbow grease to get it looking like it was. Most people don't care about that as much. They just want a tip. Good luck with it!
Great "tip"! Thanks. I've got a large crapola stainless kitchen knife from the supermarket that I put out when guests are staying for extended periods here and I'm not there. Most recently, the knife was dropped by someone who stayed here (hence, my placing my beloved carbon steel knives under lock and key when I'm not there) and the tip is toast. I resharpened the edge but didn't want to reshape the tip for the reason you mention--radically changing the profile of the edge.
 
That first repair got my confidence up! No pics, but I got the chips out of a trio of Pampered Chef knives (one coated green, two "forged German steel") and a Japanese pocket knife my buddy uses as a box cutter.

Of the four knives, that Pampered Chef santoku was a real bear. Beyond the chips there were perpendicular cracks in the edge. I read something about overstressed steel, and just kept removing metal until I got past them. That knife in particular was still annoying to sharpen! It didn't seem to want to let go of the burr on one side! It might have been me, Idk, but I got it sharp enough.

My aunt who owns the knife uses a pull-through sharpener. My guess is that all the cracks and chips in her knives were caused by the edge skipping across the angled sharpening device.

This is pretty fun stuff!
 
The stone arrived early!

Here are some after shots:

View attachment 1428483

View attachment 1428485

I obviously didn't repair the tip. It's still not perfect, but it is in much better shape than when I started!

I have until Sunday; I may give it another go. There's one tiiiiiiiny chip that I can't see, but I feel it with my fingernail. I know that'll come out easily enough.

@cotedupy outlining and sketching a plan before the repair was a really helpful idea, thanks for that!

@ChefJohnBoy-ardee I'm still not ready to try tip repair. The spine idea is a pretty good one though. I may ask to borrow this knife again down the line and try it.


Nice work!

If you do go after the tipping at some point - John's suggestion above is a good one. Taking all or almost all of the material off the spine is a very easy way to do it, as the steel is softer and you don't have to re-do the main bevel grind.

I tend to do more 50:50, in order to mimic the original profile as exactly as I can, but it's a much longer and trickier process. And in terms of actual use - it doesn't really make much difference one way or the other.
 
I had no idea the steel is softer on the [email protected]! I just saw how thick it was, and how much I'd have to remove to make it pointy, and decided against it.

Ah well, there are always more knives :)
Depends on how the knife was made, was it forged or drop forged... That Pampered Chef knife is probably german stamped and milled down in China. Usually pretty hard, hence the chipping. Usually really thick behind the edge needing lots of regular thinning and heavy. Am I close? It is the same way with most Mercer knives finding their way into commercial kitchens instead of Dexters.

On an unrelated note but semi related, I finally made time for a few knives to hit the stones. My butchery knives, a Chef Works boning knife, Konosuke Sujihiki and a name that I don't remember Yanagiba that I got from Blue Mountain; plus my Dao Vuo Cleaver and Spyderco Delica 4. I didn't get to my gyuto that needs heavily thinned, my deba or pettys.

The Suji barely needed any work. The yanagiba felt dull but sharpened quick. I was surprised by this. I remember single beveled knives needing more time. Maybe because the grind was all mucked up at the factory (probably why it was $30).

The cleaver took an edge quick and I was able to get it flatter on left side to make it better for a right handed person. It has since slayed a massive amount of vegetables.

The boning knife was borked. I don't know how I've been breaking down as much as I have with it and not crying more.

Oddly enough sharpness on a knife effects how they cut proteins. I broke down 200# of salmon for an event after working on my knives and they felt dull when trying to skin the sides.

Went onto do 170# of NY Strips. They went through those like a hot knife through room temperature butter. If I would have been breaking down beef tenderloins I would have been cussing because the knives would have been too sharp and cut through the silver skin instead of peeling it. Chef life problems...

No pictures. No one in my kitchen has time for that.
 
Depends on how the knife was made, was it forged or drop forged... That Pampered Chef knife is probably german stamped and milled down in China. Usually pretty hard, hence the chipping. Usually really thick behind the edge needing lots of regular thinning and heavy. Am I close?

Spot on. Pretty heavy for its size. My aunt actually gave me one of the same knives many years ago. It was great out of the box, but I couldn't figure out how to use a honing steel on it. I ended up trying it in a few different pull-through sharpeners, and one electric, and it just wouldn't hold an edge. I didn't know a dang thing about sharpening then. I still don't, but I also didn't ;)

It was what I thought of as "my first decent knife." It's funny how that bar keeps moving...
 

Tirvine

ancient grey sweatophile
That first repair got my confidence up! No pics, but I got the chips out of a trio of Pampered Chef knives (one coated green, two "forged German steel") and a Japanese pocket knife my buddy uses as a box cutter.

Of the four knives, that Pampered Chef santoku was a real bear. Beyond the chips there were perpendicular cracks in the edge. I read something about overstressed steel, and just kept removing metal until I got past them. That knife in particular was still annoying to sharpen! It didn't seem to want to let go of the burr on one side! It might have been me, Idk, but I got it sharp enough.

My aunt who owns the knife uses a pull-through sharpener. My guess is that all the cracks and chips in her knives were caused by the edge skipping across the angled sharpening device.

This is pretty fun stuff!
My hazy memory of a pull through sharpener was that it was excellent for soft tomatoes. That slightly ragged fresh edge really grabbed and cut soft tomatoes well. Of course my big Chef's knife (10" carbon Sab bought in the '60s), sharpened and polished on water stones, does a decent job with soft tomatoes too (understatement).
 

Tirvine

ancient grey sweatophile
Its fun to look at how others do things but then you did it the way I would do it. Cinderblocks can work if you don't have a hard coarse stone but that may be the redneck in me coming out. *Thumbs up!*
Rednecks usually figure things out pretty darned well. This one learned how to hone a razor on the rolled edge of a sink when he was sixteen.
 
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