Can this be fixed? Badly chipped Yu Kurosaki.

[Scubadoo]

So I went to get my Yu Kurosaki 165mm AS Bunka out of the knife draw, and somehow it has developed two nasty chips and two little ones and the heel is knicked. Wife and kids say they have no idea what happened . To be fair the edge is thin as! so I'm suprised it didn't happen sooner!

Question is, can it be fixed at a cost that makes it worthwhile? The knife cost 200€ just over two years ago.

The tip of my Yoshikane petty also got lost a while ago but i managed to grind a gentle curve to the top to meet the cutting edge (used a CBN wheel). Changed the profile a bit but it works fine. Any advice appreciated. I'm a woodworker so pretty handy, and used to sharpening tools but have never ground or thinned a knife.
Cheers
Dave

 

[Delat]

By coincidence I watched this Kurosaki repair video (the first one) the other day as one of those bunkas is on my radar.




And here’s my own experience as a complete noob repairing the edge on my Yoshikane
https://www.kitchenknifeforums.com/threads/yoshikane-skd-folded-edge.53987/#post-820789

 

[Bolek]

Have you tryed to us it as is ?

 

[Matus]

Reprofile (to remove the chips) then regrind (to get a thin edge again). By hand on stones that will be a few hours ...

 

[Scubadoo]

By coincidence I watched this Kurosaki repair video (the first one) the other day as one of those bunkas is on my radar.




And here’s my own experience as a complete noob repairing the edge on my Yoshikane
https://www.kitchenknifeforums.com/threads/yoshikane-skd-folded-edge.53987/#post-820789

Thats great mate, thanks, I'll give it a watch.

 

[Scubadoo]

Have you tryed to us it as is ?

I have, yes. It snags and catches on food. And tea towels. Not a lot of fun to use.

 

[Scubadoo]

Reprofile (to remove the chips) then regrind (to get a thin edge again). By hand on stones that will be a few hours ...

Thanks. Having not done it before, is it likely that I could ruin the knife? It has quite a concave grind. Would you do it on full sized stones or use smaller ones? I have a 6" grinder with a CBN wheel but don't fancy doing that without a jig.

 

[esoo]

If you're on Instagram, Tosho has had a few posting of fixing knives much worse that that.

 

[Matus]

Thanks. Having not done it before, is it likely that I could ruin the knife? It has quite a concave grind. Would you do it on full sized stones or use smaller ones? I have a 6" grinder with a CBN wheel but don't fancy doing that without a jig.

Before I get too smart about it - do look at the links provided, and also google for the blog of Greg (wabocho) as he has detailed articles to several different knfie restorations.

With that said - don't worry about the concavity - the only reason it is there is, because it is the simplest and cheapest grind to be made on a large grinding wheel. It would be gone sooner or later as no user has the possibility to follow it when thinning the knife. I would recommend to 'first 'design' how the new profile should look, draw it on the blade and grind the steel off. Then in the second step have a closer look how is the blade thick on the new edge and then go to town on a coarse (but not too soft) stone and don't let too much mud to build up as you will otherwise be removing steel all around the place. If the knife is really thin it may not need to have quite as much steel removed - but that will also depend on what kind of new grind you want to put on it (flat or gently convexed).

 

[Scubadoo]

Before I get too smart about it - do look at the links provided, and also google for the blog of Greg (wabocho) as he has detailed articles to several different knfie restorations.
.

Thanks Matus, I've had a look at the wabocho website but it's pretty hard to find the right threads on the blog. But i'll keep looking.

And thanks for the guidance. I'll do some research and decide if i want to have a go at it.

 

[Scubadoo]

If you're on Instagram, Tosho has had a few posting of fixing knives much worse that that.

Thanks, have followed and will have a look from some relevant posts.

 

[esoo]

Thanks, have followed and will have a look from some relevant posts.

I'm on my work machine right now, so difficult for me to find the post, but they had a Kono Madeii that came in with huge chips in it. The fixing videos I thought were good - not straight diy instruction, but had some points about how they kept the shape of the knife.

 

[inferno]

So I went to get my Yu Kurosaki 165mm AS Bunka out of the knife draw, and somehow it has developed two nasty chips and two little ones and the heel is knicked. Wife and kids say they have no idea what happened . To be fair the edge is thin as! so I'm suprised it didn't happen sooner!

Question is, can it be fixed at a cost that makes it worthwhile? The knife cost 200€ just over two years ago.

View attachment 131408

The tip of my Yoshikane petty also got lost a while ago but i managed to grind a gentle curve to the top to meet the cutting edge (used a CBN wheel). Changed the profile a bit but it works fine. Any advice appreciated. I'm a woodworker so pretty handy, and used to sharpening tools but have never ground or thinned a knife.
Cheers
Dave

lol those are minor chips.

i chopped up a few beer cans with my kurosaki and it got a 5x5mm chip.
removed it with an atoma 400 in about 2 minutes. then 1h on the glass 500 to thin it out and make it good again.

 

[Scubadoo]

lol those are minor chips.

i chopped up a few beer cans with my kurosaki and it got a 5x5mm chip.
removed it with an atoma 400 in about 2 minutes. then 1h on the glass 500 to thin it out and make it good again.

Ha ha! Well that's good to know! I have Shapton ceramic stones, i think 300, 2000 and 6000 and a set of dia-sharp diamond plates. Also have a flat granite plate that i used with sandpaper for handplanes and such.
Will have to have a go after some research.
Cheers
Dave

 

[inferno]

go 80 or 120 grit sandpaper for the chips and keeping the profile looking as it does now. paint it on so you know how much to remove. and where.
use the paper DRY!

then when thats done you can flip the knife on its bevel and start thinning out that bevel again. i would probably go sandpaper first then revert to your coarsest stone when you see you are close to getting an actual edge on there again.

learning by doing!!

just do it.

its a 0,5-1,5h project at most.

 

[Scubadoo]

Thanks for the encouragement. I decided to have a go. I've restored plenty of old hand planes and chisels but then i'm generally using a honing jig for the irons.

I actually took the bulk of it off with a CBN wheel on my 6" grinder then fine tuned with an Atomi 400 grit Diamond stone. wish i'd had something coarser but it was OK. Then i did my best to thin the blade behind the edge by resting the grind on the stones and working on it for about an hour. It was a bit tricky due to the concave grind and there are some marks or discolouration left behind. The profile is probably flatter than before but I don't think that will be an issue. I thinned using my three Shapton ceramic stones then gave it a quick buff on a polishing wheel before putting an edge on it. Pretty pleased with how it came out and it was a good learning exercise.

I suppose i could have spent some time with flexible sanding pads or sand paper in the hand to even out the scratches but at the end of the day that won't make it cut any better!

The second photo is after the grinding wheel and the third is the finished knife.

Thanks everyone!

 

[phoka]

It looks very nice, great job!

 

[drsmp]

From your photos looks like you need to thin more above the edge ? A choil shot would be helpful

 

[drsmp]

Here’s my Fujin AS 210 for a reference

 

[Dhoff]

go 80 or 120 grit sandpaper for the chips and keeping the profile looking as it does now. paint it on so you know how much to remove. and where.
use the paper DRY!

then when thats done you can flip the knife on its bevel and start thinning out that bevel again. i would probably go sandpaper first then revert to your coarsest stone when you see you are close to getting an actual edge on there again.

learning by doing!!

just do it.

its a 0,5-1,5h project at most.

wHat is the benefit of using the sand paper dry contra wet?

 

[Scubadoo]

I think you're probably right, it could do with some more thinning at the heel. What do you think?
I found it hard to thin with the concave grind.

 

[inferno]

wHat is the benefit of using the sand paper dry contra wet?

it lasts 10 times longer.

 

[Jason183]

I think you're probably right, it could do with some more thinning at the heel. What do you think?
I found it hard to thin with the concave grind.
View attachment 131612

You don’t really need to thin if there’s still some concavity unless you have giant wheel grinder(For concave sharpening). Just keep using the knife and sharpening the edge only until the the concave grind becomes flat, then it’s time to thin, cutting feel probably won’t be the same after it becomes flat grind, but will be more robust.

 

[Scubadoo]

I actually took it back to the stones for an hour and worked on it some more. It's a pretty flat grind now with a bit of convex to it. And the scratches are much more uniform now.
That was a fun learning experience!