pros and cons of the convex grind

RescueRiley

RescueRiley

Joined
Mar 22, 2006
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I've heard alot pf people talk about thier preferences for a complex grind on a psk I was wondering why...I'm currently in the VERY early stages of designing my own knife and would like to be well informed on different grinds before I settle on one...was interested in learning a little more about this.. Thanks.
 
Hey Double R...

Not sure if there are any cons to a convex grind..

I'm still getting use to them myself..Only ones I have are on my moras,,and a couple Fallknivens...

They sharpen up like frigging Crazy though....

I'm not expert on knife grinds,,so I'll let someone with more experience tell you the ins and outs of them..

ttyle

Eric
O/ST
 
the sharpest grind you can put on a knife is the hollow grind, but it's also the weakest. inversely the convex is the strongest and least sharp. still, a convex grind on thin enough stock will give you a resilient edge that is quite sharp and resists binding. build it with well treated, quality steel and you've got a keeper.

also some find it relevant that as you sharpen a flat knife you gradually move back toward the spine and get a thicker edge. convex sharpening supposedly keeps the edge consistent. i don't quite buy any part of that one.
 
Before I start blabbin', let me just say I'm a student of this stuff, not an expert. My opinions are based on my own experience and I could be totally wrong.

Convex grinds... it depends on how you how you define one, and how it's applied. To many folks, simply feathering back the original edge a bit makes it "convex." This is true, sort of, since you no longer have a V at the edge, more like the thin end of an appleseed. On the other hand, a full convex grind makes a full, smooth sweep from edge to spine. If you really wanted to, you could say a piece of roundstock has a convex grind, but that would be silly.

The first example may hold its edge a little longer, it may not. I have noticed this in my knives, but I can't quantify it. They held an edge pretty good beforehand.

It may cut more smoothly, this seems reasonable to me and has been my experience. No hard, crisp angle to catch on. A hollow grind cuts even more smoothly, for the same reason, less drag. Until you hit the flat of the blade.

Sharpness won't increase unless you decrease the angle you sharpen at and/or increase the polish of the edge bevels. I don't care what style of grind it is.

With a full convex grind, the advantages are more pronounced. But only if the blade is wide and thick enough. I think drag/binding is the biggest factor at play here, as Magnum22 said. That's not much of an issue on a Mora. On a 1-1/2 wide, 5/16" thick Bowie, it definitely can be an issue. There is a maker here who also regrinds (usually large) production knives to a full convex, and his customers rave about the increase in performance.

Magnum22 said:
also some find it relevant that as you sharpen a flat knife you gradually move back toward the spine and get a thicker edge. convex sharpening supposedly keeps the edge consistent. i don't quite buy any part of that one.
Click to expand...

I disagree, sort of... of course you can keep the cutting performance more consistant with a convex grind, if you're really keeping that same sweep/arc as you get into the thicker part of the knife. If you sharpen normally, that edge (which is more obtuse than the blade grind) will get wider and wider. Draw a 40 degree angle (pretty standard sharpening angle) on a scrap of paper, and cross it where it's 1/8" apart. Doesn't look so sharp now, eh? ;)

But I don't quite buy it either, because if you have to sharpen that far into the blade of your knife for it to make a difference, you either use it a HECK of a lot or the heat-treat is way, way off.

I like convex grinds, full and partial. I put them on the knives I like best and use most, and they perform better. Especially the big ones, they certainly chop and split wood better. But it's not a magic bullet by any means.

The cons are, you will scuff up the finish on your knife.
 
There is always confusion when talking about convex grinds. Do you mean convex grind/edge or do you mean just convex edge? You can put a convex edge on any grind. Alot of makers do flat grinds with convex edges. A hollow grind can have a convex edge. I think most of the talk is more about convexing the edge on a knife more so then the actual grind. To compare a hollow grind with a convex grind is like comparing apples and oranges. They are complete opposites but both can have convex edges. Alot depends on what the knife is going to be used for. I only do convex grinds/edges. I always ask what the knife will be used for. If it is strickly going to be for slicing and finer work I recommend thinner stock like 1/8". The mid section of a convex grind is thicker then a flat or hollow so it will move material better but will take a little more effort because of the added resistance. It is also stronger because of this. A convexed edge is easy to sharpen. I use a EZE-Lap rod sharpener and a flat two sided sharpener. I hold the knife in my weak hand and sharpen from heel to point going away from the edge rolling off the edge. Then I strop on my jeans. With a little practice, you'll be surprised how easy it can be.
Scott
 
No cons whatsoever. Its the strongest. It tends to not stick. And IMO, once you're used to it, its the easiest to maintain.

Also, when learning to make, its a pretty easy one to learn to grind.
 
I like it on some of my knifes (covex edge), but I find that on s normal v grind would give you slightly sharper edge, but with the bigger knifes, I find convex to be a better compramise btw sharpness and durability.
 
In my experience, convex edges tend to hold up better, and my 3 or 4 sharpest knives all have convex edges on them. :D
Saying a convex edge will not get as sharp I think is deceiving. Convex will never be as thin as a V bevel, and many have stated that as a sharpness issue.
Anyone that has not tried out a good convex edge should. For me, convex is the way to go, but I know it isn't for everybody.

David
 
Scott,
I know what convex edges and grinds are, and know how to sharpen them, but one thing I keep hearing doesn't make sense to me:
What makes a convex edge easier to sharpen than a flat edge? There is more motion involved to get a consistent curve, and more steps as well if you sharpen flat, and then convex it by changing the angle and/or stropping it. Is it simply because you don't have to be as precise as you do with a flat edge, or am I missing something.
 
I think that at least for cutting ability it is really the thinness of the edge that makes the difference in the cutting whether it is flat ground, scandi or convex.

I believe a thin convex is really no more durable than a thin any other grind and a thick convex is no different than a thick V grind or scand grind on a thick blade.

I do think that a convex is slightly easier to sharpen because the way most folks sharpen them the angle is not so much an issue.
 
I should clarify...
I have some very thin convexed edges as well, but what i meant was at an equal angle, a convex edge will never be quite as thin as a V bevel...
Just the geometry of it. However, that geometry is why that kind of edge is soo good for slicing and chopping. It pushes the cut material out of the way, and the material doesn't bind on the blade.
I would go for the convex every time.

David
 
simms65 said:
I should clarify...
I have some very thin convexed edges as well, but what i meant was at an equal angle, a convex edge will never be quite as thin as a V bevel...
Just the geometry of it. However, that geometry is why that kind of edge is soo good for slicing and chopping. It pushes the cut material out of the way, and the material doesn't bind on the blade.
I would go for the convex every time.

David
Click to expand...

I'm with you now:thumbup: :D
 
Jamesh Bond said:
Scott,
I know what convex edges and grinds are, and know how to sharpen them, but one thing I keep hearing doesn't make sense to me:
What makes a convex edge easier to sharpen than a flat edge? There is more motion involved to get a consistent curve, and more steps as well if you sharpen flat, and then convex it by changing the angle and/or stropping it. Is it simply because you don't have to be as precise as you do with a flat edge, or am I missing something.
Click to expand...

HD, made a good point. the angle is not as much of an issue as with a V-edge. That's why you don't need to be worried about a consistant angle like a V-edge. You can't go too steep sharpening a convex edge because you will blunt it. You can sharpen a convex edge on a flat stone but it takes more practice learning to roll the edge as you sharpen down the blade. I've found doing it holding in your hand, it's easier to roll off the edge. It's tough to explain. So much easier to show someone. I think they cut better because there are no sharp angles (abrupt stops) like a v-bevel has. Same thing as a hollow grind where the grind stops half way up the blade. A high hollow grind IMO is a better slicer but it's a weaker grind because it's much thinner across the mid section (less material there).
Scott
 
I tend to favor v grinds simply because I've been doing them for years, I've got my method, and I'm pretty good with them. I tend to dull convex edges when I sharpen them.

Having said that, I've had several knives from Scott and he put a convex edge and grind on them, and they did last a good long time. I suspect if I could spend a half an hour with him, I could probably sharpen convex also. There's something to be said for a good demo. There's also something to be said for only needing to carry sandpaper in the woods for sharpening also, I can see where this would be really handy.
 
I think the really important thing is to realize that talking about different grind without measurements it completely useless. Really the relevant measurements are edge angle, thickness behind the edge, spine thickness and primary edgebevel angle.

If you were running a flat grind from spin to edge with no edgebevel (zero edge) you would indeed have an edge angle that is smaller than you can achieve with a convex grind, you can only get below that angle with a hollow grind to zero edge or by reducing the spine thickness. It will be obvious if you draw this out on paper.

However, in most cases an edgebevel is applied in which case a convex blade may very well be thinner and have a smaller edge angle than a V-grind: Case and point, most manufacturers run a V-grind (lets say a full flat) with an edge grind around 20 deg. per side. BRKT runs their knives with a convex grind with a terminal angle (angle of the very edge) of about 13 deg. per side.....much, much thinner than most V-grinds. So you have to be careful that you compare similar geometries.

RRiley: I think you first have to make up your mind, what you want to use your knife for and pick appropriate "measurements". Not only blade-length, -height and stock thickness, but also how thick you think the edge should be and how acute. Once you have decided on the basic geometry, you can strengthen the edge without adding much thickness by mirobeveling, or convexing. If you expect significant binding in your applications convexing will reduce binding. If you want to further thin the thickness behind the edge you can hollow grind it without reducing the strength of the very edge.

I think the easiest way is to draw a very much enlarged model that is proportionally correct on a piece of paper and play around with the different geometries. Most of these things should become very apparent.
 
Scott, a couple more questions, please:
When you use an EZ Lap sharpener to do your convex ground blades, are you just touching the cutting edge? If so, doesn't this have the same effect as with flat ground blades and edges (the edge getiing progressively thicker over the life of the knife)? Also, how long does it take you to strop a coarse edge, like one left by a diamond EZ Lap, on your jeans? I just convexed my first two blades today (partial convexes, edge area), and after finishing with the 1000 grit paper, I STILL had to strop better than 50 times a side on my loaded leather!!
Can you elaborate a bit more for a confused man? Sorry, please, and thank you!!
 
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