working with concave grind

[noj]

I know this has been asked before, but perhaps in different ways. I read quite a bit before asking. I am seeking methods for working with concave grinds on double bevel knives. This would include wide bevel with most of the blade road concave (ie concave cross section). It would also include blades ground convex near the edge, but turns concave as one moves up towards the spine (concave in cross section). In both cases, if you put the knife on a flat stone (in order to maintain, polish, or thin), you end up with a long region along the blade where the stone doesn’t touch.

I have seen advise suggesting leaving it alone (perhaps for cutting performance), grinding it flat (possibly a little convex) all at once, or over time as it needs maintenance. Performance in the kitchen is my main goal, but I also enjoy making it look good also. I find working on a fully CONVEX (oops .. said "concave" in original post) blade (or blade road if wide or single bevel) most comfortable. I’d might like to get there before 15 years of maintenance.

Almost every knife I have purchased has this issue, except for something like a Masamoto ks monosteel. Most of mine are San-Mei with reactive core and cladding. I have made attempts to remove it on older and inexpensive knives, but it’s a time consuming and elaborate process. I am seeking to learn more. Comments or questions welcome. Thanks in advance.

 

[user 16756]

JMO though.

 

[JaVa]

I think my view differs from most, but For now just leave it if it's very thin behind the edge and if the concave grind rides high towards the spine.

That concave shape makes it possible for the grind to be super thin behind the edge and go higher than other grind types. Which ads to the performance. So you can keep sharpening it for way more times without sacrificing performance. If you flatten that concave part the performance you seem to prefer will change.

Only when you feel a drop in performance is it time to start thinning. At that point it'll be a little more work to sort it out, but it should take a looong time to get to the point when you need to start thinning.

I know most will tell you to just flatten the concave out because of the amount of work might be coming later. I don't get that at all. I have several gyutos with lovely concave grinds and love those knives for it. I wouldn't want loose what attributes that style brings to the table.

I use mine in busy pro kitchen all the time and even with that much constant use and regular sharpening none of them has yet needed thinning because that grind rides so high they don't seem to start getting thicker behind the edge ever. I don't no when I'll ever reach the point I need to thin them. I have no idea what others do with their knives, how much and often do they use or sharpen them, to suggest that just kill that concave before it's too late.

Only time I would (and have) thinned that concave grind away is if it's wonky and uneven on a new knife. Which makes me think it's probably left there by accident and wasn't meant to be there in the first place or the smith just left it too roughly finished.

 

[JaVa]

...Also, why buy a knife with an intended concave grind if all you want to do is ruin it by getting a rid of that grind?

 

[noj]

...Also, why buy a knife with an intended concave grind if all you want to do is ruin it by getting a rid of that grind?

Why? Most knives bought years back (didn't know), couldn't tell by looking, purchased online, etc.

 

[user 16756]

...Also, why buy a knife with an intended concave grind if all you want to do is ruin it by getting a rid of that grind?

hard to ruin a knife by making it cut better.

I dont like hollow grinds at all in the kitchen (like them a lot for pocket knives though). Some great knives at ground on wheels and as a consequence are hollow. It's a shame but if that's the only way to get a wide bevel from Yoshikazu Tanaka or Kenji Togashi's shop then them's the breaks. I know it's reductive to think in terms of "best" when it comes to grind because there are tradeoffs to everything, but for me the best knives range from slightly convex to very convex, and I have absolutely zero issue nuking the out of the box grind if necessary. if the knife is too valuable for me to do that to or gonna be a pain, I simply wont buy it though, which is why when it comes to certain lines of stainless clad knives, e.g. those from the two I just said, I strongly prefer fully convexed knives from the outset.

also there is no "time to thin". if you sharpen the edge you should raise the shinogi/grind line by the same amount anyway.

 

[Pie]

I know this has been asked before, but perhaps in different ways. I read quite a bit before asking. I am seeking methods for working with concave grinds on double bevel knives. This would include wide bevel with most of the blade road concave (ie concave cross section). It would also include blades ground convex near the edge, but turns concave as one moves up towards the spine (concave in cross section). In both cases, if you put the knife on a flat stone (in order to maintain, polish, or thin), you end up with a long region along the blade where the stone doesn’t touch.

I have seen advise suggesting leaving it alone (perhaps for cutting performance), grinding it flat (possibly a little convex) all at once, or over time as it needs maintenance. Performance in the kitchen is my main goal, but I also enjoy making it look good also. I find working on a fully concave blade (or blade road if wide or single bevel) most comfortable. I’d might like to get there before 15 years of maintenance.

Almost every knife I have purchased has this issue, except for something like a Masamoto ks monosteel. Most of mine are San-Mei with reactive core and cladding. I have made attempts to remove it on older and inexpensive knives, but it’s a time consuming and elaborate process. I am seeking to learn more. Comments or questions welcome. Thanks in advance.

What exactly are you looking for? Like flattening it out, or turning it into a full convex? Coarse stone if you’re crazy, power tools or sandpaper if you’re less crazy. If it’s performance you seek, you could potentially thin it and leave it ugly, or do a full sandpaper refinish. Hollow ground knives are generally pretty thin bte, and take longer to get thick than flat/convex grinds. That doesn’t mean it never needs thinning though.

One way or the other it’s going to be somewhat involved, requiring time and a few steps at least. My experience convexing a concave grind was arduous, so I probably won’t try it again for funsies or if I can help it.

 

[noj]

What exactly are you looking for? Like flattening it out, or turning it into a full convex? Coarse stone if you’re crazy, power tools or sandpaper if you’re less crazy. If it’s performance you seek, you could potentially thin it and leave it ugly, or do a full sandpaper refinish. Hollow ground knives are generally pretty thin bte, and take longer to get thick than flat/convex grinds. That doesn’t mean it never needs thinning though.

One way or the other it’s going to be somewhat involved, requiring time and a few steps at least. My experience convexing a concave grind was arduous, so I probably won’t try it again for funsies or if I can help it.

The knives of interest to me are all supposed to be convex, or flat wide bevel. By supposed to be I mean according to a vendor, maker, or (and not suggesting anything negative) this forum. What I find after I get them is different. It is convex within ~10 mm of the edge. The area above that is often slightly concave. I suspect it's due to how they were made, and not a design feature. It does make and re-finishing, kasumi, polishing work on a stone problematic.

When I say "slightly concave" I have no clear way to quantify that. I have tried grinding low spots on some old knives for practice. It was a lot of work. I don't know if the effort would be comparable. I definitely don't want to damage my better knives. I have no worries about sharpening single or double edge, but I just don't have much experience in this area.

 

[Pie]

The knives of interest to me are all supposed to be convex, or flat wide bevel. By supposed to be I mean according to a vendor, maker, or (and not suggesting anything negative) this forum. What I find after I get them is different. It is convex within ~10 mm of the edge. The area above that is often slightly concave. I suspect it's due to how they were made, and not a design feature. It does make and re-finishing, kasumi, polishing work on a stone problematic.

When I say "slightly concave" I have no clear way to quantify that. I have tried grinding low spots on some old knives for practice. It was a lot of work. I don't know if the effort would be comparable. I definitely don't want to damage my better knives. I have no worries about sharpening single or double edge, but I just don't have much experience in this area.

Ahhh I see what you mean now. It’s unfortunate they’re not all proper convex bevels, one would expect a knife of that caliber to deliver as advertised. Depending on the knife, and the specific case the amount of work could vary. It could be terrible or it could be fairly reasonable. I imagine if it’s a low spot the whole length of the blade it would be
unpleasant.

In terms of potential damage, fixing geometry and lows should theoretically be ok as long as you’re careful, but aesthetics will most likely suffer unless your polishing skills are pretty good.

 

[JaVa]

Yeah, I miss read the original post. The "I find working on a fully concave blade most comfortable." really threw me off and I thought we were talking about knives that were actually designed to have a fully concave grind like S.Tanaka nashiji, which I absolutely love specifically for it's grind (well, steel too actually). Personally in general I really don't jive well with wide bevel knives unless they'r clearly concave.

Seems like this has more to do with the wonky roughly finished category. Munetoshi KU is known for this. Then I would just keep sharpening and thinning like you do with other knives. The problem will correct itself eventually.

Those low spots usually won't have any negative effect on cutting performance. If they do, then just knock off the shoulders by rounding them or get the shoulder line higher.

If it bothers you visually then have closer look at post #2.

 

[TB_London]

Low spots look scruffy when thinning if you leave them.

I used to work them out as leaving bevels looking rough would annoy me. I have found that a bit of stone mud on the end of a cork rubbed over the bevel can blend it all together and have it looking presentable whilst the dips are worked out over time.

if you can keep away from the edge and work some convexity into the bevel as you go all the better.

 

[northside]

...Also, why buy a knife with an intended concave grind if all you want to do is ruin it by getting a rid of that grind?

Are they intended to be concave, though? Many Japanese knives are ground on a water wheel so are concave as a result of the tool used and not so much as a design. Obviously s-grinds and ‘hollow’ grinds are a different story, along with intentional concave grinds like a single bevel yanagi/etc. Just wanted to point out that not all knives are designed to be convex - it may just be convenient or cost effective with the tooling available to the producers.

 

[JaVa]

Are they intended to be concave, though? Many Japanese knives are ground on a water wheel so are concave as a result of the tool used and not so much as a design. Obviously s-grinds and ‘hollow’ grinds are a different story, along with intentional concave grinds like a single bevel yanagi/etc. Just wanted to point out that not all knives are designed to be convex - it may just be convenient or cost effective with the tooling available to the producers.

Well I think I wrote pretty specifically about intended concave grind. I think that means when it was made that way intensionally. As in designed that way. Right?

If you read my previews post I thought I also mentioned what I think if it wasn't intentional?
If it's designed that way and works why change it? If it's a flaw and it bothers you, nothing wrong with fixing it.

The way I see it hollow, concave and S-grind are about the same thing. If a grind is concave it's called a hollow grind and doesn't every hollow grind transitions into an S-grins at some point when it hits the shoulder?

Then there's the Dahlman style S-grind where that S-shape gets emphasized when his convex grind hits the hollow part in the blade face. Almost like a reverse S-grind? Kinda?
Or maybe it's the other way around?

That's the way I perceive it anyway. Could be wrong though?

 

[noj]

Yeah, I miss read the original post.[snip]

You didn't mis-read it, I mis-wrote it! ;-) Sorry about that. Will catch up on the replies.

 

[northside]

Well I think I wrote pretty specifically about intended concave grind. I think that means when it was made that way intensionally. As in designed that way. Right?

If you read my previews post I thought I also mentioned what I think if it wasn't intentional?
If it's designed that way and works why change it? If it's a flaw and it bothers you, nothing wrong with fixing it.

The way I see it hollow, concave and S-grind are about the same thing. If a grind is concave it's called a hollow grind and doesn't every hollow grind transitions into an S-grins at some point when it hits the shoulder?

Then there's the Dahlman style S-grind where that S-shape gets emphasized when his convex grind hits the hollow part in the blade face. Almost like a reverse S-grind? Kinda?
Or maybe it's the other way around?

That's the way I perceive it anyway. Could be wrong though?

Yep - I’m with you on those points. I just think it’s worth pointing out to some that just because a knife comes a certain way out of the box it may not mean much more than it is that way because it was convenient to make it that way.

An s grind is usually done on a much smaller contact wheel than a typical concave grind. An 8 or 10 inch wheel is fairly common for an s-grind whilst a 48 inch radius platen is on the smaller side for a concave grind in a kitchen knife. The same but different.

 

[noj]

Thank you all for your comments. I’d like to ask a closely related question. What knives would you recommend that don’t have "this" issue. Let me be more specific.

* want to be able to practice maintenance, kasumi, polishing without major rework or re-profiling
* prefer flat to convex surfaces(*) so I can work on typical stones
* minimum of hollows to fix
* let’s restrict to double bevel, San-Mei, gyuto or petty
* prefer traditional carbon core steels, Wa handle

Suggestions for brand, and specific model (if it matters) welcome. Don’t consider price (not that I don’t). If this doesn’t make sense, please clarify, and I will re-work the question. Thanks in advance.

--------------------
(*) by surfaces I mean blade road if wide bevel, or entire blade of not

 

[ian]

Are they intended to be concave, though? Many Japanese knives are ground on a water wheel so are concave as a result of the tool used and not so much as a design. Obviously s-grinds and ‘hollow’ grinds are a different story, along with intentional concave grinds like a single bevel yanagi/etc. Just wanted to point out that not all knives are designed to be convex - it may just be convenient or cost effective with the tooling available to the producers.

What exactly is the difference between "intentionally concave" and "concave because it was ground on a water wheel"? Presumably the person grinding it was aware it would come out concave. If by "intentionally concave" you mean "the performance will be better if it's concave than otherwise", that's kind of subjective.

GL finding some convex or flat ground wide bevels, OP. You could also just ask a retailer this question -- shoot someone at the usual places (JKI, JNS, KNS, Carbon, Clean Cut, Strata) a question asking which of their knives has a nice flat or hamaguri wide bevel with uniform geometry that will be easy to polish. I'm sure you'll get some good suggestions.

 

[noj]

What exactly is the difference between "intentionally concave" and "concave because it was ground on a water wheel"? Presumably the person grinding it was aware it would come out concave. If by "intentionally concave" you mean "the performance will be better if it's concave than otherwise", that's kind of subjective.

GL finding some convex or flat ground wide bevels, OP. You could also just ask a retailer this question -- shoot someone at the usual places (JKI, JNS, KNS, Carbon, Clean Cut, Strata) a question asking which of their knives has a nice flat or hamaguri wide bevel with uniform geometry that will be easy to polish. I'm sure you'll get some good suggestions.

Thanks Ian for the GL, and phone call idea (I'll give it a shot).

Other ideas from your (meaning anyone reading this) experience welcome, and of course will not be taken as any sort of "guarantee";-)

 

[JaVa]

What exactly is the difference between "intentionally concave" and "concave because it was ground on a water wheel"? Presumably the person grinding it was aware it would come out concave. If by "intentionally concave" you mean "the performance will be better if it's concave than otherwise", that's kind of subjective.

I think there's a miss use in the terminology and actually the unintentional concave talked about here really means low spots in the grind?

And sure hollow grinds benefits are subjective like every other design feature on a knife. Just like some like thin knives and some thick ones. it's all subjective.

But for me there are several benefits to hollow grind. The knives I like to use the most have that. Like the Tanaka nashiji ginsan. Mine weighs 207g, so it's positioned firmly in the middle weight category. It really has some heft to it. Still it cuts like a laser. That can only be achieved is with hollow grind.

It's a wide bevel and super thin behind the edge. The first 1,5cm in the grind it's basically as thin as any laser I have. So not just behind the edge but it goes a bit higher. After that initial 1,5cm it beefs up pretty fast to pronounced shoulder at 2cm. So I get 1,5cm of laser like performance and then that outward shoulder pops food of the blade. So I get so many benefits that I personally value. That initial laser like glide, but with authority from the weight and topped off with decent food release.

If it were a flat wide bevel, it would be thicker behind the edge. Or to achieve the same thinness it woud have to have even higher grind and then you loose some of that authority from being lighter and less food release. a pure convex grind would just be fatter behind the edge.

For some reason basic flat wide bevels have always seemed kinda lifeless to me. Haven't yet found one that felt as good to me as hollow- or convex grinds. You know, subjectively.

I also have a Wakui with hollow to convex grind and that one is just as nice as the Tanaka if not even better.

 

[JaVa]

Thanks Ian for the GL, and phone call idea (I'll give it a shot).

Other ideas from your (meaning anyone reading this) experience welcome, and of course will not be taken as any sort of "guarantee";-)

Are you looking for a SS, SS clad carbon or full carbon?

 

[noj]

Are you looking for a SS, SS clad carbon or full carbon?

Prefer full carbon, not absolute requirement