Is convexity overrated?

[jacobwilder5]

I’m in the middle of a project that calls for some serious thinning and I’ve been worried about losing the slight convex grind that it has.

It got me thinking about how important that really is? I kind of understand the science behind why convex helps cutting performance but is it really that impactful vs. other common grinds like flat or concave? Outside of thinness behind the edge, are there other things more important to consider?

Being somewhat of a novice I’m interested in hearing what folks have to say about the topic and their experience.

 

[user 16756]

Every truly flat ground blade Ive used for cutting food has had MAJOR stiction.

 

[ReiHamono]

You want it for strength above all, but with that said I flatten everything perfectly at 120 grit then I start to focus on the steel more around 1-2k to bring in a slight convex grind

If you don’t want stuff to stick with a thinned edge polish with coarser stone until desired effect is achieved

 

[instantramen]

I once ground a Kochi to a flat grind, and it became a laser with lots of stickage but simply ghosted through food. My Mazaki on the other hand still has its convexity, and while it doesn't fall through food as effortlessly as the flat ground Kochi did, the cutting action is more buttery and there's something satisfying about how it shoulders food out of the way. Food still sticks, but less so and easier to brush off.

So in my limited experience: convex is more about smooth, velvety cutting feel while flat is perhaps easier to thin/maintain. A more experienced sharpener may not notice the difference in maintenance though and focus more on replicating that cutting feel by preserving the convex. If you're after food release, consider a Takeda

 

[Tethien]

I’ve thinned my knives mostly flat and I thin them a bit more near the edge so it’s slightly convex but still polishes like it’s totally flat, I’ve had some pretty good results on food release on some knives and at worst the food release is ok, only some foods have sticking issues but even convex knives have some trouble with it. I’ve had great results with performance too, all of the knives I’ve thinned preform at yoshikane level or better. My top performer is leagues above a regular sld yoshikane it’s insane, it’s also doesn’t feel that chippy for how insanely well it preforms

 

[fatboylim]

Hollow grind is great for lazering through tough vegetables like Winter squash and sweet potato. But it sacrifices good release.

Convex grind is great for gliding through food with better food release. It can still work OK on tougher vegetables but really shines on everything else.

 

[ThirdJewel]

.

 

[Choppin]

Most of my knives have convex geometry and when thinning I usually try to maintain that.

I don’t find it too hard to do so, I’d say give it a try. At least it should be an interesting challenge.

Jon’s videos can help. There is one on single bevel hamaguri sharpening, I sort of use the same technique on double bevels. Here is a text explanation: On single bevel sharpening- Hamaguri and Beta Togi

 

[JayS20]

Every truly flat ground blade Ive used for cutting food has had MAJOR stiction.

Stiction or stickage/sticking?

Hollow grind is great for lazering through tough vegetables like Winter squash and sweet potato. But it sacrifices good release.

You mean concave. Hollow can help with smoother cutting but also lead to better food release depending on execution.

A good convex grind is hard to produce. Have experienced that with many makers. To hit the sweet spot of good FR and smooth cutting experience isn't an easy task.

Convex grinds help with FR and also with sticking. You need a force which pushes the produce away from the blade. A thick blade does that but you lose an easy cutting performance and will still have problems with stickage. Often times convexity will be introduced slightly above the edge to have that effect and it definitely helps. But you are quickly getting into too thick territory. If you sharpen free hand there is a good chance you will add some convexity. Unless you sharpen with a pressure and angle guided system you won't sharpen the edge completely flat.
Overall convexity is definitely not overrated, even with special grinds like Hooks, hollows... you need to introduce some to get the best performance but rarely any makers accomplish really good convexity especially when it stands on its own.

 

[Benuser]

I use after thinning a SP2k — an aggressive 3k — to find where when edge leading any resistance remains starting almost flat and giving only one light stroke and looking for the next one. It allows to eliminate the last traces of facetting. After this the very edge is likely to need some touching-up as debris were moved into its direction.

 

[captaincaed]

Some oldies but goodies

 

[ethompson]

Not underrated at all. Two of the most beloved makers on here - Kato & Kippington - are known for their convex work. Anyone who's used a kippington can tell you just how good convex can be. Tasteful convexity lets you get the most out of any knife IMO. Even on low wide-bevel knives where it may not seem like it can do much it'll let you control shinogi placement and geometry behind the edge separately.

 

[captaincaed]

Dan Bidingers true talent is convex grinding, in my mind. The Bgrind rocks, but it needs a good convex base grind behind it to work well. And it does.

Mario was known for it back in the day too. I’m sad I never tried one.

 

[nakiriknaifuwaifu]

You want it for strength above all, but with that said I flatten everything perfectly at 120 grit then I start to focus on the steel more around 1-2k to bring in a slight convex grind

If you don’t want stuff to stick with a thinned edge polish with coarser stone until desired effect is achieved

Flattening completely, then reconvexing to lose more height, and then recommending moving to coarser grits to limit stiction on a mostly flat bladeroad is a confusing recommendation.

Convex ftw.

Granted, there are some cases where convexity isn't as advantageous - Takedas take well to a flat/scandi grind, petties with small blade roads have little real estate for sticking and stacking, etc. - but for the vast majority of chef knives - especially those with wider bevels covering 50% of the height of the blade - it is helpful to have a complex bevel if you wish to have a balance between cutting performance, drag/stiction, and food release. Convexity allows you to determine the particular balance and from an aesthetic point of view it allows you to vary the shinogi height and geometry bte independently. Edit: forum large hand man @ethompson has already said this

 

[stringer]

+1 for convex

Strength plus precision.

Flat grinds suck.

Food release yada yada.

And an s grind doesn't work without the convex bit.

The thread title makes me cringe every time it gets bumped.

Can we consider this one asked and answered yet?

 

[jacobwilder5]

Can we consider this one asked and answered yet?

Haha yes.

In short:
Convex = GOOD. Flat = BAD. Convexity NOT overrated.

Thanks all, I learned a lot on this thread.

 

[stringer]

Haha yes.

In short:
Convex = GOOD. Flat = BAD. Convexity NOT overrated.

Thanks all, I learned a lot on this thread.

You have done the community a great service. Next time someone asks we have an easy thread to point them to. Might need to make it a sticky

 

[fortheloveofmoar]

I guess the next question is how can you sharpen convex on a stone? If something is flat how do you make it convex?

 

[captaincaed]

Consider yourself schooled

Works on double bevels just as well.

 

[Choppin]

Consider yourself schooled

Works on double bevels just as well.

That works well, it’s what I [try to] do

 

[ReiHamono]

That’s what happens when ideology meets reality.

The overwhelming majority of people sharpening their own knives don’t have the desire to take this any further than either a micro bevel and/or a flat and thinned bevel.

Hell, most people with knives refuse to sharpen themselves, polishing is even worse

 

[superworrier]

IMO convexity is overrated and people are kind of chasing buzzwords. Example is that Birgersson is well-loved even though it has a concave grind but at the same time people **** on Takefu knives for having hollow grinds. Obviously, the grinds are different, but probably most people might dismiss Birgersson off the type of grind if there weren't so many good reports.

 

[HumbleHomeCook]

IMO convexity is overrated and people are kind of chasing buzzwords. Example is that Birgersson is well-loved even though it has a concave grind but at the same time people **** on Takefu knives for having hollow grinds. Obviously, the grinds are different, but probably most people might dismiss Birgersson off the type of grind if there weren't so many good reports.

As you know, people go gaga over different knives and makers for different reasons well beyond grind and in some cases even true performance.

Honest question, how are you differentiating between concave and hollow? The depth of the grind or the height? I mean a hollow grind is concave... Sorry if I misunderstood.

 

[superworrier]

As you know, people go gaga over different knives and makers for different reasons well beyond grind and in some cases even true performance.

Honest question, how are you differentiating between concave and hollow? The depth of the grind or the height? I mean a hollow grind is concave... Sorry if I misunderstood.

They’re the same to me

 

[HumbleHomeCook]

They’re the same to me

Okay me too.

 

[Delat]

IMO convexity is overrated and people are kind of chasing buzzwords. Example is that Birgersson is well-loved even though it has a concave grind but at the same time people **** on Takefu knives for having hollow grinds. Obviously, the grinds are different, but probably most people might dismiss Birgersson off the type of grind if there weren't so many good reports.

I really liked my Yu Kurosaki, although I don't think I ever checked to see if it was hollow or convex. I think the TKV knives are generally very good performers especially at their price point.

Maybe I'm just a phiistine, but I don't generally bother to inspect the grind of my knives to see if they're convex or concave. I just try them and see how they cut. If I'm happy it goes into the rotation, if it wedges then at that point I'll take a closer look to see if I want to tackle the thinning or not.

I think it was a solid year that I thought my Yoshikane was concave just because I saw some posts saying they were. When I finally checked I was shocked to see that it was actually convex

 

[captaincaed]

The distinction is high and low bevels. Low bevels can tolerate flat or concave grind. High bevels suck that way.

 

[Barmoley]

Okay me too.

They are the same to everyone or they should be, same thing.

 

[ACHiPo]

The distinction is high and low bevels. Low bevels can tolerate flat or concave grind. High bevels suck that way.

Can you clarify what you mean by high and low bevels? It seems a convex grind is (or could be) a series of microbevels, with the primary blade road being at a lower angle than the subsequent bevel(s) closer to the edge. I'm trying to understand how that translates to high or low bevel.

Thanks.

 

[jedy617]

I really liked my Yu Kurosaki, although I don't think I ever checked to see if it was hollow or convex. I think the TKV knives are generally very good performers especially at their price point.

Maybe I'm just a phiistine, but I don't generally bother to inspect the grind of my knives to see if they're convex or concave. I just try them and see how they cut. If I'm happy it goes into the rotation, if it wedges then at that point I'll take a closer look to see if I want to tackle the thinning or not.

I think it was a solid year that I thought my Yoshikane was concave just because I saw some posts saying they were. When I finally checked I was shocked to see that it was actually convex

Me too. I don't fuss too much, I either like something or I don't and move it along. Hollow ground cuts great...it's just not something you want if you are into polishing.