Pros & Cons: Convex vs. Concave vs. Flat vs. Multi Bevel

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wacki

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Sep 12, 2009
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Just like the title says. What's the pros & cons of Convex vs. Concave vs. Flat vs. Multi Bevel?
 
This is a huge can of worms. It all has to do with slicing performance vs. chopping performance vs. edge strength and more. A lot of what I've read here is as much myth as it is science. I buy the knives that I like and I don't worry so much about the type of edge.
 
bdmicarta said:
This is a huge can of worms. It all has to do with slicing performance vs. chopping performance vs. edge strength and more. A lot of what I've read here is as much myth as it is science. I buy the knives that I like and I don't worry so much about the type of edge.
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What this guy said. If its cutting performance chisel grind is what your looking for.
 
Robert,

Every time the subject of chisel grind comes up, posters are about 95% negative. It seems you are pro chisel grind. Care to elaborate?
 
Hollow Grind FTW!!!!!!

:D

You'll be hard pressed to find a better slicer than one of Dozier's wicked deep hollow grinds. For me, my favorite is the flat grind/saber grind. I think they are sexy, and they know it.

Moose
 
Just got into trying the multi-bevel/micro=bevel.

It's a very interesting idea, and I'm liking the results. Especially after a light strop.
 
wacki said:
Just like the title says. What's the pros & cons of Convex vs. Concave vs. Flat vs. Multi Bevel?
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Pros and cons for what? Shallow cutting? Deep cutting? Edge retention? Ease of sharpening?

Your threads tend toward asking questions that are so broadly posed that they are unanswerable.
 
wacki said:
Just like the title says. What's the pros & cons of Convex vs. Concave vs. Flat vs. Multi Bevel?
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Good luck in your quest. Eventually you will learn its something you will need to experience for yourself to understand. Getting others opinions on the subject will never give you the answers you are looking for.
 
seelow123 said:
Yeah go chisel grinds woo!

It's nice to see people still appreciate them.
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Chiselgrinds make s me think of the planersteel in Grandpa's old woodplaner, made out of hardwood.
The steel has a chiselgrind and an adjustable plate on top of the steel, to adjust the angle of breaking away the curls.
Softwood means low angle and hardwood means increased angle for effective planing.
It's like an adjustable convex edge depending on the density of the wood.

Regards

Mikael
 
IMO, the answer should depend on your intended use (like ALWAYS). One of the reasons I hate one-sentence questions with little to no description of why it's being asked, what the intended use is, etc.

Convex is great for choppers, to my mind. Puts more metal behind the cutting edge, and the geometry functions like a wedge to split the material, but with relatively minimal friction, due to the geometry.

Concave is good for slicers. Again, the geometry keeps the material from binding against the blade, while you have less material behind the edge, which generally tends to be good for slicing.

I'm not quite sure if there's any mechanical advantage to a flat grind for any particular use. I think of them as a compromise between concave and convex grinds. You don't get the mechanical advantage of the curve, but you do get a middle ground of metal behind the edge. So they'll be more slicy than a convex, and more choppy than a concave, at least to my mind. And, like Moose, I think they're just sexier.

As marcinek pointed out, the more information YOU provide US, the more helpful OUR responses will be to YOU. More description in the OP = good.
 
There are two ways at looking at your question, already in the answers you'll see what I mean. I think better terminology would have helped as some answers seem to be going at it from the final bevel point of view and others from the main grind point of view. I'm pretty sure you mean the latter as getting a concave final bevel would be an interesting and probably fruitless attempt. The confusion likely stems from the "multi-bevel" part of your question as sharpening gurus will tout the benefits in certain instances of micro bevels. Please excuse the very basic drawing, it'll just help with visualizing what I'm about to waffle on about!
bevels.jpg

This shows a micro bevel at the edge, also technically a mutli-bevel, but I'll be referring to the main grind.

As was mentioned, it all depends on what you're cutting and how. For example:

Large kitchen knives for vegetable prep, an understated, full height convex is your friend.
General day to day utility in a folder/small fixed blade - honestly a Moo point, you'll likely never notice the difference but I'd lean towards hollow and full flat.
Choppers (I mean competition grade wood-whacker types) convex again, basically a crossbreed between knife and axe for obvious reasons.

As far as multi-bevel grinds like Loveless' duplex grind, it all depends. If it makes sense to you instantaneously and you can see why it was done, it'll probably suit you. Some makers, do multi-bevels just for the aesthetic value. Multiple bevels are likely to add drag when slicing and/or force you to only use a short section of the blade at any one time. To get the faceted look, their thicknesses need to vary and on a couple knives I've seen it cause the grind with the lowest height to be very, very chunky and for all intents and purposes useless.

I'll give a few broad pros and cons but you need to realize there are so many determining factors in each category eg:

Hollow grinds
A hollow grind achieved with a small diameter wheel will perform very differently from a hollow grind from a large diameter wheel.

Same thing but in the reverse for convex grinds (closer to flat will slice better than closer to an axe)

Multi bevels - are they all the same type? one hollow and one flat/convex or any imaginable combination?

All of the grinds will be affected by their height. The higher the grind height, the "slicier" it will be. Simple physics here, thinner profiles will part material easier than thicker profiles.

So for a couple broad strokes:
Hollow grinds
One of the easiest grinds to achieve, thus why factory knives often sport them :)
When cutting, the first bit of the blade entering the material is one of the thinnest so for shallow cuts they are fantastic. As the blade moves deeper, the accelerating curves of the grind cause binding. For a real world example, go cut a potato with a classic hollow grind, easy at first but requiring more effort the deeper you cut.
As I said, on a daily basis the average Joe won't notice this, all depends what you're cutting...
Grind height is a factor, Dozier grinds were brought up for good reason ;)
Sharpening is pretty easy as on a properly ground blade there is quite a bit of thin area that will be very easy to touch up.

Flat grinds
I like flat grinds, they part material really well, they're both thin behind the edge and retain a lot of strength as less material is removed when compared to hollow grinds. They are harder to achieve as when grinding by hand, even a slight shift of pressure can completely ruin it. Machines can give you consistant results but I make my stuff by hand so my opinions are based on my experience.
Sharpening's pretty easy but the additional steel means it likely thickens faster than a hollow.

Convex grinds
Also very hard to do and very much dictated by the intended end use. I like paper thin convex grinds on my gyutos but you need a lot more meat on a chopper. if not done right they wedge like hell, sharpening is a point of contention as some feel that stropping will remove material over the whole surface maintaining a sharp edge but to my mind, their "life" is short as after a few good sharpens you're going to be in some pretty thick steel. You could have it re-ground by a maker or even attempt it yourself but at some point it will likely need a touch up.

Multi bevels
Too big a can of worms for me to even attempt :D Far too many factors! In general, probably more gimmick than real-world but there are some out there that make sense. Broadly speaking, you can apply the same pros and cons I've listed depending on what grinds are used but you have to add in the probable friction caused in the transition zones.

Hope this helps!

Gazza
 
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jnichols2 said:
Robert,

Every time the subject of chisel grind comes up, posters are about 95% negative. It seems you are pro chisel grind. Care to elaborate?
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A far sharper angle on the cutting edge + less surface area on the cutting edge = slice thru shit with ease. Take a needle and push it into your friend. Sure he will feel it and it will go in easily. Take a nail and push this into your friend. Not so easy in fact may take some stabbing motion for penatration. Thinner is better and please don't really stab your friends
 
As my cutting and sharpening skills evolve the performance of my knives change. I've found that flat scandi, convex scandi, full convex, convex with secondary convex, flat with secondary convex, and flat with secondary flat are all good for different reasons and no so good for others. Multi grinds and hollow grinds were weeded out of my decision process very early on due to maintenance issues and cutting performance.

Everyone has different skills and demands they place on their knives, which translates into preferences for everything including material, size, ergonomics, and geometry. What may seem obvious today seems silly tomorrow. I personally find a lot of people I know starting out with a taste for hard use knives with thick stock and obtuse bevels and gravitating toward thinner stock with more carefully considered material and ergonomics. I also find a lot of people gravitating toward shorter blades as they learn how to cut stuff. The only person I currently know who thinks bigger is better is my 14 year old nephew, but even he will admit he doesn't need anything more than a simple Mora.

I know I digressed, but ultimately I think YOU are your own best answer and you should get a couple knives with a range of differences and go field test them in whatever way is applicable to you. Take your time, as sometimes it takes weeks or longer to discover that convex grinds sharpen easily on rocks and microbevels aren't always a sign of a maker's inability to properly apply an edge (although sometimes this is indeed the case).
 
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