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Overgrind Into The Edge

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Dave Martell

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I just stumbled upon an old picture that I shot of a brand new knife that came in for sharpening years ago. I began sharpening the knife but a problem quickly arose that got worse and worse. I think this image clearly shows the irreparable condition of a blade overgrind....


 

Andrew H

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Nice picture, thanks!
 

Dave Martell

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I forgot to mention that this was one of the first knives that I got burnt on trying to fix the overgrind. Yeah there's nothing like buying someone a new knife all because someone else screwed the pooch.
:angry2:
 

GlassEye

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Thanks for the image and explanation. My CCK looks like this in a few spots, it is getting annoying.
 

Dave Martell

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Thanks for the image and explanation. My CCK looks like this in a few spots, it is getting annoying.

You might get lucky and see it disappear as you sharpen over time. I say that because CCK's have hammer marks near the edge more so than overgrinds. Still though, an errant hammer blow can show the same irreparable condition too, you never know.
 

Don Nguyen

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Is there any way to check for this? How much does it affect the performance?
 

memorael

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Hey Dave, in order to "fix" this couldn't you just thin the knife a lot? in the case of the knife being a mono steel? That is however totally changing the knife but its the only thing that comes to mind in order to "fix" it.
 

l r harner

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wqas ging to say i woudl jsut grind it thinner till it was again even
 

Lefty

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Or shorten the blade, from edge to spine, until you're past the overgrind. In the case of the CCK, the blade height would allow this more readily, of course.
 

Dave Martell

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I tried the thinning method here because it looked straight forward but as I approached the edge bevel the hole opened up huge and the edge started to disappear thus I got screwed. On the surface that method seems like the way to go but 9 out of 10 times it doesn't work unless you can figure out a way to keep the belt from touching the overground section while doing the thinning to the rest of the knife. I realize that this is hard to accept but when you see it first hand it can't be denied.
 

Lefty

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Makes sense to me, Dave. :D
 

mikemac

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...And the CCK is a $40 +/- mass produced rustic blade from a developing nation....rational expectations and all.


You might get lucky and see it disappear as you sharpen over time. I say that because CCK's have hammer marks near the edge more so than overgrinds. Still though, an errant hammer blow can show the same irreparable condition too, you never know.
 

memorael

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O I get it, its hard to grind everything except the hole... damn hope I don't get a lemon ever.
 

Sarge

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For you Dave it probably isn't worth the time and effort but if at home someone were to thin by hand on stones, wouldn't it be possible to avoid creating a massive hole?
 

heirkb

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For you Dave it probably isn't worth the time and effort but if at home someone were to thin by hand on stones, wouldn't it be possible to avoid creating a massive hole?
That's what I was wondering. Thinning on something like a diamond plate perhaps.
 

Dave Martell

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For you Dave it probably isn't worth the time and effort but if at home someone were to thin by hand on stones, wouldn't it be possible to avoid creating a massive hole?

That's possible, I'll never say never
 

TB_London

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I keep thinking about this, for simplicity assuming a 50/50 grind and a 50/50 edge, if the hole doesn't go past the centre of the thickness of the blade, would you still be able to have an unaffected edge, other than it being thinner behind that part? I thought the problems came when the hole crossed the centre of the blade and interfered with the edge.
 

Eamon Burke

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I keep thinking about this, for simplicity assuming a 50/50 grind and a 50/50 edge, if the hole doesn't go past the centre of the thickness of the blade, would you still be able to have an unaffected edge, other than it being thinner behind that part? I thought the problems came when the hole crossed the centre of the blade and interfered with the edge.
If it does that, your knife is SOL forever.

You can sharpen a knife like this, but it's tedious, and the bevel will always look wavy at the shoulder and it will be weaker there because it's thinner. Plus if you put it on a honing rod, your hole pops right back up.
 

StephanFowler

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I keep thinking about this, for simplicity assuming a 50/50 grind and a 50/50 edge, if the hole doesn't go past the centre of the thickness of the blade, would you still be able to have an unaffected edge, other than it being thinner behind that part? I thought the problems came when the hole crossed the centre of the blade and interfered with the edge.
The problem is moreso that when you sharpen the knife normally you will end up with an area of the blade that doesn't contact the board, and without correction it will just get worse and worse
 

TB_London

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it will be weaker there because it's thinner.
Agreed, but if the remediation is thinning the blade to a uniform thinness, the weakness shouldn't be a concern-or you'd be weakening the whole edge?

I'm trying to see why the edge won't make board contact if the steel that actually forms the edge is still present. So long as you are using stones that won't follow the hole and make it deeper, in the way that a belt will, in my head you should still be able to get even board contact, the same ad if you thinned away the steel to remove the overgrind. Unless the overgrind has removed your 'edge forming steel'
 

Eamon Burke

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So long as you are using stones that won't follow the hole and make it deeper, in the way that a belt will, in my head you should still be able to get even board contact, the same ad if you thinned away the steel to remove the overgrind. Unless the overgrind has removed your 'edge forming steel'

That would be true if your sharpening technique is solid, your stones are dead flat, and abrasives are larger than the overgrind. This means use of a honing rod, aggressive strops, even the wear and tear of normal use will just make the hole show right back up. It will be a constant source of frustration. Also, the burr you will build up trying to get down to that edge will be a honker, and then you use it and it chips out/wears down, and then you have the hole again and have to grind off the entire blade to meet it again.

Also, to fix it properly, you'd need to abrade the ENTIRE knife evenly, or else you'd end up creating a new grind problem somewhere on the knife.

One of the reasons to buy a really good quality hand made knife is that there ARE guys making knives without any sort of overgrind at all--and they are a BREEZE to sharpen. Makes life a lot easier.

You aren't wrong, it's just that the management of such an issue is so frustrating it's like having a car that is permanently misaligned.
 

Lefty

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If you ask me, the only real way to solve this problem is by taking the blade, treating it as a sheet of (whatever type of steel), creating a new profile that is higher up the blade than the hole reaches, and starting anew. Essentially, taking a gyuto and making a short suji, or a cleaver and making a nakiri.
 

Andrew H

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If you ask me, the only real way to solve this problem is by taking the blade, treating it as a sheet of (whatever type of steel), creating a new profile that is higher up the blade than the hole reaches, and starting anew. Essentially, taking a gyuto and making a short suji, or a cleaver and making a nakiri.
The amount of work required to do that kind of change would be huge.
 

Lefty

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Nothing a tile saw with a good blade/water-cooled angle grinder and a bench sander can't handle. :)
 

Andrew H

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Nothing a tile saw with a good blade/water-cooled angle grinder and a bench sander can't handle. :)
And quite a bit of skill to make anything more than a knife shaped object.
 

EdipisReks

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One of the reasons to buy a really good quality hand made knife is that there ARE guys making knives without any sort of overgrind at all--and they are a BREEZE to sharpen. Makes life a lot easier.
i've now handled three Shigefusas, and none have this issue, so i think you are right. ;)
 

stevenStefano

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I've only ever seen this on one of my knives and it is near the heel anyway so it doesn't bother me too much to be honest
 

TB_London

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Sorry if I'm coming across as argumentative, I'm just trying to get my head around it as it seems in practicality over grinds cause more issues than I can attribute conceptually. Plus I'm so used to writing technical reports my writing style can be a bit to the point.

This means use of a honing rod, ........, will just make the hole show right back up.
As the honing rod is running along the bevel which is flat, I would have thought it wouldn't follow the hole, as it is in the blade face?

Also, the burr you will build up trying to get down to that edge will be a honker
I don't follow why I'd make a bigger burr, conceptually if I sharpen as normal I'd still hit the edge all along in the same way as if the over grind wasn't there. The bevel won't look even, but it will be.


I think I'll make up some mock blades out of wood tomorrow and try to help explain my rationale. They may make the issues stand out clearer as well

Cheers for the answers so far, guess I've been lucky in that over grinds haven't really been an issue on any of my knives yet.
 

Dave Martell

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Here's some more fun overgrind pictures to take a look at. This was a new knife that the customer used but NEVER sharpened. This is the Moritaka Effect! :lol2:

To be fair to Moritaka this was a long time ago and it is the worst one I've ever seen. Still though, it does show the typical Moritaka effect that they still do today, although they do it on a much smaller & harder to see scale than this.

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