Here's a good link with useful information about convex grinds:
http://home.nycap.rr.com/sosak/convex.htm
http://home.nycap.rr.com/sosak/convex.htm
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Convex and V Grind Questions
- Thread starter C Bryant
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I like a nice fine convex for pretty much everything. It's got good cutting power, bites deep, and keeps on cutting even when a casual stroke with the thumb suggests it is now blunt. I like the way cut material flows across in a way unmatched by other blades I have / have had.
Same as hollowdweller, convex edges are much easier for me to maintain.
Kinda similar to hollowdweller again; The worst for me is a V grind with a coated blade. Although I'm speaking specifically in terms of the edge as opposed to the grind here, the SRK I bought for my brother is a good example. That had little cutting power. His method of remedy was to sharpen it up on a really rough stone, in accordance with some ill conceived notion of micro sawing. Had he let me strip the black crap off and convex the edge to a fine finish even that lumpen SRK would have cut pretty well. I've seen others that have done it so I'm certain of that.
There is also too much emphasis put on shaving sharp. Just because a knife doesn't stay shaving sharp doesn't mean it won't cut.
I totally agree with what Scott said here too. I blatantly took the piss with a comment of cheese wire sharp on this forum before in recognition of the preoccupation with; shaving sharp, razor sharp, scalpel sharp, cuts like a laser, cuts like a light saber, cuts like ...pick your own clusterfvck epithet... I don't get any of that. Knives are tools designed to perform a specific range of tasks [hopefully], and being a razor blade isn't usually one of those tasks. True, it is a nice demonstration of ability to be able to easily bring a knife up to the point at which hair will pop, but it tells you very little about how well a blade will function at what it was designed to do. As above, a convex will usually keep on cutting at the tasks it was designed to do long after the ability to pop hair is gone. Yet, and especially if you finish to a very high grit, the performance will level out there and keep on doing what it was meant to do long after alternatives have fallen off the graph. That's my take on it anyway.
Jerry Hossom makes some interesting observations of the quirks of the convex below. Although to be clear, some of the angles he is on about are far from what I'd consider having cutting power. I would reject a knife ground in such a way. But it is informative to see what he is observing at the extremes:
Yeah, it can become an addiction.
There is another side effect of this process as well. It's inflicted on us through the understanding (maybe discovery without understanding) that what we thought we knew about sharp and sharpening and even steel becomes a little less certain.
By taking an edge down to ridiculously sharp, which you can readily do this way because removing metal and reshaping edges is easy, you gain a better understanding (or confusion without understanding) of the qualities of steel. Everything becomes exagerated when the edge is too thin. You can see the effects of even small impacts on the edge. If you thin the edge in small steps with different steels you can gain a sense of their properties and capacity to handle the tasks they're asked to perform. You will see that some steels will take a much finer edge than other steels (the wire edge I mentioned above will simply drop off the edge of some steels before others, leaving some less sharp than those which "might" have a finer grain stucture). You can see how a "toothy" edge holds up compared with a polished edge. Some steels will crack on impact, some will deform, even though both may be at the same hardness. (That one challenges our understanding of what Rc hardness is and what it may or may not measure.)
You can see that by simply convexing the last millimeter or so of that edge allows it to cut as well or better than a flat or nearly flat beveled edge and is less prone to the effects you previously observed. That it's more robust is not surprising; that it cuts better. Some will say, "of course, axes have convex edges and cut through hard wood very easily," I'm not talking about a 5# axe head moving at 100mph; I'm talking about a steak knife. Even then, I've seen a "properly" sharpened machete outchop a hatchet with a well sharpened 2# head, both moving at similar speeds.
You then discover that convex edges cut when by conventional wisdom they shouldn't. I'm almost reluctant to bring this up because the flat bevel folks will use it as clear evidence that I'm as crazy as they thought I was.
When you sharpen on a slack belt, you can make the belt deflect so that the final edge angle is very steep, maybe 40-50 degrees. And yes that creates an included edge angle of 80-100 degrees. If you put that angle on a flat bevel it won't cut anything, yet the convex edge cuts very well, and will continue to cut long after a flat bevel at a shallower angle has become completely dull.
You'll find that a polished convex edge at a final angle far exceeding anything you thought was useable will cut well and will still be cutting well longer than you ever imagined.
I have some thoughts about why this is, but I'd rather not share those because someone might send the people with the wrap around jackets and padded cells after me. The point is that if you care to look at this carefully, you will see things about sharp, sharpening and steel that will themselves become an addiction - it will drive you nuts. Why the hell does this thing works like it does?
The final included angle of the edge on the machete that easily sliced through 2" sapplings and still shaved was 100+ degrees. Shaved at 100+ degrees? Go figure.
Hossom - 09-21-06 05:20.20
In conclusion, for the way I use knives, the convex does everything best.
Same as hollowdweller, convex edges are much easier for me to maintain.
Kinda similar to hollowdweller again; The worst for me is a V grind with a coated blade. Although I'm speaking specifically in terms of the edge as opposed to the grind here, the SRK I bought for my brother is a good example. That had little cutting power. His method of remedy was to sharpen it up on a really rough stone, in accordance with some ill conceived notion of micro sawing. Had he let me strip the black crap off and convex the edge to a fine finish even that lumpen SRK would have cut pretty well. I've seen others that have done it so I'm certain of that.
There is also too much emphasis put on shaving sharp. Just because a knife doesn't stay shaving sharp doesn't mean it won't cut.
I totally agree with what Scott said here too. I blatantly took the piss with a comment of cheese wire sharp on this forum before in recognition of the preoccupation with; shaving sharp, razor sharp, scalpel sharp, cuts like a laser, cuts like a light saber, cuts like ...pick your own clusterfvck epithet... I don't get any of that. Knives are tools designed to perform a specific range of tasks [hopefully], and being a razor blade isn't usually one of those tasks. True, it is a nice demonstration of ability to be able to easily bring a knife up to the point at which hair will pop, but it tells you very little about how well a blade will function at what it was designed to do. As above, a convex will usually keep on cutting at the tasks it was designed to do long after the ability to pop hair is gone. Yet, and especially if you finish to a very high grit, the performance will level out there and keep on doing what it was meant to do long after alternatives have fallen off the graph. That's my take on it anyway.
Jerry Hossom makes some interesting observations of the quirks of the convex below. Although to be clear, some of the angles he is on about are far from what I'd consider having cutting power. I would reject a knife ground in such a way. But it is informative to see what he is observing at the extremes:
Yeah, it can become an addiction.
There is another side effect of this process as well. It's inflicted on us through the understanding (maybe discovery without understanding) that what we thought we knew about sharp and sharpening and even steel becomes a little less certain.
By taking an edge down to ridiculously sharp, which you can readily do this way because removing metal and reshaping edges is easy, you gain a better understanding (or confusion without understanding) of the qualities of steel. Everything becomes exagerated when the edge is too thin. You can see the effects of even small impacts on the edge. If you thin the edge in small steps with different steels you can gain a sense of their properties and capacity to handle the tasks they're asked to perform. You will see that some steels will take a much finer edge than other steels (the wire edge I mentioned above will simply drop off the edge of some steels before others, leaving some less sharp than those which "might" have a finer grain stucture). You can see how a "toothy" edge holds up compared with a polished edge. Some steels will crack on impact, some will deform, even though both may be at the same hardness. (That one challenges our understanding of what Rc hardness is and what it may or may not measure.)
You can see that by simply convexing the last millimeter or so of that edge allows it to cut as well or better than a flat or nearly flat beveled edge and is less prone to the effects you previously observed. That it's more robust is not surprising; that it cuts better. Some will say, "of course, axes have convex edges and cut through hard wood very easily," I'm not talking about a 5# axe head moving at 100mph; I'm talking about a steak knife. Even then, I've seen a "properly" sharpened machete outchop a hatchet with a well sharpened 2# head, both moving at similar speeds.
You then discover that convex edges cut when by conventional wisdom they shouldn't. I'm almost reluctant to bring this up because the flat bevel folks will use it as clear evidence that I'm as crazy as they thought I was.
When you sharpen on a slack belt, you can make the belt deflect so that the final edge angle is very steep, maybe 40-50 degrees. And yes that creates an included edge angle of 80-100 degrees. If you put that angle on a flat bevel it won't cut anything, yet the convex edge cuts very well, and will continue to cut long after a flat bevel at a shallower angle has become completely dull.
You'll find that a polished convex edge at a final angle far exceeding anything you thought was useable will cut well and will still be cutting well longer than you ever imagined.
I have some thoughts about why this is, but I'd rather not share those because someone might send the people with the wrap around jackets and padded cells after me. The point is that if you care to look at this carefully, you will see things about sharp, sharpening and steel that will themselves become an addiction - it will drive you nuts. Why the hell does this thing works like it does?
The final included angle of the edge on the machete that easily sliced through 2" sapplings and still shaved was 100+ degrees. Shaved at 100+ degrees? Go figure.
Hossom - 09-21-06 05:20.20
In conclusion, for the way I use knives, the convex does everything best.
Last edited:
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.......One of the weird things I have seen on some blades lately is a really nice full convex grind to the BLADE, ending in a steep V grind at the edgeTalk about a tease!.......
Yes, that one is a killer. Some I have handled are basically ground like a cold chisel. You can beat the snot out of it, but it won't make smooth cuts in wood, especially if you're doing much more than shaving a thin curl off. I have wondered if some makers feel this is necessary becasue someone is going to try cross-baton seasoned hardwood with dirt and grit in the bark and then complain publicly when "the edge didn't hold up."
I am glad someone of some significant merit stepped up and said that.:thumbup:
If you're only using your knife to shave with - OK. If your barber batons a few sticks and makes some fuzzies with his razor before giving you a shave, you'd mess yourself. Then too, in reference to the ones HD mentioned above, those obtuse secondary bevels can be made shaving sharp but are pretty worthless for working wood. I have edges you can actually touch without getting bit, but apply the least pressure or swipe across it and you're open. Won't shave hair but will cut you faster than you can imagine and will cut wood with ease for a long, long time.
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I've noticed this too. But frankly it is not much of a turn on for me. I guess I'm just conditioned to love the feel of an edge that grabs you.
The moderate attitudes on this thread are impressive given the contraversy that this topic usually raises. In the end, we all have different methods that we learn work for us and our applications.
I love my mora #1 for its ability to shave even curls off of wood - a perfect whittler and carver. However, I don't carry it most times because it doesn't meet other criteria that I like a knife for.
Similar thing goes with sharpening. I get the performance I want with the grind of my choosing. Even though a grind may be more efficient in another application, I might not be as confident keeping the edge that way. For practical purposes, I really don't like having every knife I own with a different bevel and grind combination. I'd need a database just to track down how to approach maintenance of each inventory item.
As a V-grind person that means I usually stick to 2 angles a steeper one for the cutters and a shallower one for the heavy duty tools. Thats about as complicated as I get, even if it means some elbow grease at the beginning to reset the knife to where I like it.
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I've honestly struggled with the shaving sharp thing a lot. And the "cuts like a laser" term has been applied to several of my knives.
So, here goes- I know how to vary my convex edges, and it really does depend on the use. I got for a broader and thinner convex on a skinner than I do on a bushcrafter- precisely because people DO do a lot of cross grain cutting with the BC blade. Here's a thing, that has been brought up a few posts back- the final bevel angle isn't the important part, it's the grind away from the edge- thinner for slicing, a bit thicker (anyone who knows my blades knows that doesn't mean thick) for a utility or BC type blade. Pretty much what Scott said, ain't it?
I've learned to have very little concern for chipping edges out with the convex geometry. It still worries me, but it honestly used to wake me at night, and at this point people have chopped down trees with large 1/8 inch thick blades I've made. I'm VERY happy with the durability of a convex edge on 57-61 rc carbon steel. Period.
Cuts like a laser? I don't cut cigarette papers, or wet newspaper, or whatever. I do have a "feel" for how a blade works through shaving arm hairs and cutting leather (we often use knives that are being made for orders to cut out the sheath pattern as part of the testing of the final sharpening). I don't pop hairs. I do a smooth bevel against the skin draw cut, and that's it- it seems to measure the smoothness of the sharpening job better than anything else. I don't have nerve endings in paper.
Cuts like a laser, to me, means it cuts easily, deeply, and tracks straight. All good things.
One thing that has taken my more recent knives to the peak of performance, thus far, is the stropping. I sharpen to 600 grit, then strop until the bevel is polished. That's it, that's the trick. Strop.
I sharpen V grinds for friends, but no longer have a knife of my own that I sharpen that way, and don't make them. I think that they are less durable, but easy to get 'okay sharp' quickly with a pocket stone or a lackie collins wheel sharpener. (edit to reinforce a point) - it is not at all impossible to get a REALLY sharp edge on a V grind.
I do scandi grinds, and I think that the ones I do make a better type of fine slicer than a convex edge in terms of shaving, but I just think they don't last as long in woodcraft.
A local gunsmith is going to be torture testing some skinning and field knives of mine, and I'm going to try out some 11 degree angle scandis, we'll see what the end result is. I suspect the convex is going to win simply because stropping is the easiest thing to do in the field when you hands are full of half skinned bear.
So, here goes- I know how to vary my convex edges, and it really does depend on the use. I got for a broader and thinner convex on a skinner than I do on a bushcrafter- precisely because people DO do a lot of cross grain cutting with the BC blade. Here's a thing, that has been brought up a few posts back- the final bevel angle isn't the important part, it's the grind away from the edge- thinner for slicing, a bit thicker (anyone who knows my blades knows that doesn't mean thick) for a utility or BC type blade. Pretty much what Scott said, ain't it?
I've learned to have very little concern for chipping edges out with the convex geometry. It still worries me, but it honestly used to wake me at night, and at this point people have chopped down trees with large 1/8 inch thick blades I've made. I'm VERY happy with the durability of a convex edge on 57-61 rc carbon steel. Period.
Cuts like a laser? I don't cut cigarette papers, or wet newspaper, or whatever. I do have a "feel" for how a blade works through shaving arm hairs and cutting leather (we often use knives that are being made for orders to cut out the sheath pattern as part of the testing of the final sharpening). I don't pop hairs. I do a smooth bevel against the skin draw cut, and that's it- it seems to measure the smoothness of the sharpening job better than anything else. I don't have nerve endings in paper.
Cuts like a laser, to me, means it cuts easily, deeply, and tracks straight. All good things.
One thing that has taken my more recent knives to the peak of performance, thus far, is the stropping. I sharpen to 600 grit, then strop until the bevel is polished. That's it, that's the trick. Strop.
I sharpen V grinds for friends, but no longer have a knife of my own that I sharpen that way, and don't make them. I think that they are less durable, but easy to get 'okay sharp' quickly with a pocket stone or a lackie collins wheel sharpener. (edit to reinforce a point) - it is not at all impossible to get a REALLY sharp edge on a V grind.
I do scandi grinds, and I think that the ones I do make a better type of fine slicer than a convex edge in terms of shaving, but I just think they don't last as long in woodcraft.
A local gunsmith is going to be torture testing some skinning and field knives of mine, and I'm going to try out some 11 degree angle scandis, we'll see what the end result is. I suspect the convex is going to win simply because stropping is the easiest thing to do in the field when you hands are full of half skinned bear.
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"One thing that has taken my more recent knives to the peak of performance, thus far, is the stropping. I sharpen to 600 grit, then strop until the bevel is polished. That's it, that's the trick. Strop."
Those that might like further reading on this would do well to look at this .pdf
Those that might like further reading on this would do well to look at this .pdf
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- Sep 4, 2007
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I have used vivi's knives and they are super, super sharp. However he kinda lost me on the explanation. My brain is overly dense in spots.
I find myself putting a slight convex edge on most all of my knives. I guess mainly because I have really taking a liking to the mouse pad sand paper sharpening method as well as the belt sander. The belt sander will put a scary sharp v edge on as well but requires more precision IMO.
On another note, many of my convex edges don't shave well but cut like crazy. Maybe I have not quite got it down to a fine art.
I find myself putting a slight convex edge on most all of my knives. I guess mainly because I have really taking a liking to the mouse pad sand paper sharpening method as well as the belt sander. The belt sander will put a scary sharp v edge on as well but requires more precision IMO.
On another note, many of my convex edges don't shave well but cut like crazy. Maybe I have not quite got it down to a fine art.
When I've tried convex, I've noticed this too. Mine also don't seem really sharp, but do cut pretty well, I'm just more used to thin v grinds, and prefer those.
I think, when we get down and start arguing minute - of - gnat's behind on edges, angles, and sharpening, it's all for fun. I think that most, if not all, of the regulars on this forum are perfectly capable of putting a good edge on a blade.
It's fun to push the limits in one direction or another, and then argue about it. And not take it personally, or too seriously. Call it an obsession, addiction, whatever, hopefully, it's all in good fun. While I enjoy putting an edge on a knife that can tree top arm hair, I don't have the time nor the interest to do it on all of my knives. Usually, it's for fun or for testing.
Personally, I'm continually amazed that something as "simple" as a knife, one chunk of steel, can have so much that will influence it. Steel, heat treat, geometry, edge angle and thickness, etc. You'd think that "just a knife" wouldn't be that interesting, but they are! I used to enjoy reading about guns and all their variations, now I'm more interested in knives. Go figure.
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BT - good reading thanks for that link!
I do hate this thread!. It inspired me to waste my time yet again last night. I have a nice double sided leather strop purchased from LeeValley tools. I went and bought a fresh set of 3M wet/dry sand paper strips (220, 400, 600, 800, 1000, 2000) and already have the green oxide compound.
I went to work on one of my little knives - it was a learning curve. Took my time stropping through each grit series. Went and re-reviewed the bark river website before starting. On the 220 grit, payed particular attention to the sound of the blade rasping on the strop to ensure that my strokes were indeed hitting the edge. Used the sharpy trick to verify this was the case. Worked my way through the grit series. Felt improvements in the edge sharpness as made my way up.
At the end, however, the knife still wasn't as sharp as I like it. It scraped hair but didn't really cut it off with no pressure. It would slice paper on the diagonal when using a small slicing motion but not push cut.
Then I was left with the psychological pain and distress associated with having one of my knives not as sharp as I like. You all know how traumatic this can be. Its like a dull tooth ache. I could only take it about an hour, went to the sharpmaker, reset the V and now it is sharp again.....
This is about the 20th time I've tried this. If I ever do get to one of these gatherings, I will surely bring my strops and materials just so I can learn from somebody with confident experience. I'm usually pretty okay at fine motor tasks requiring precision. I can even pull blood out of a 15 g bird with a 28 g needle. Don't know why I can't figure out the strop though.
I do hate this thread!. It inspired me to waste my time yet again last night. I have a nice double sided leather strop purchased from LeeValley tools. I went and bought a fresh set of 3M wet/dry sand paper strips (220, 400, 600, 800, 1000, 2000) and already have the green oxide compound.
I went to work on one of my little knives - it was a learning curve. Took my time stropping through each grit series. Went and re-reviewed the bark river website before starting. On the 220 grit, payed particular attention to the sound of the blade rasping on the strop to ensure that my strokes were indeed hitting the edge. Used the sharpy trick to verify this was the case. Worked my way through the grit series. Felt improvements in the edge sharpness as made my way up.
At the end, however, the knife still wasn't as sharp as I like it. It scraped hair but didn't really cut it off with no pressure. It would slice paper on the diagonal when using a small slicing motion but not push cut.
Then I was left with the psychological pain and distress associated with having one of my knives not as sharp as I like. You all know how traumatic this can be. Its like a dull tooth ache. I could only take it about an hour, went to the sharpmaker, reset the V and now it is sharp again.....
This is about the 20th time I've tried this. If I ever do get to one of these gatherings, I will surely bring my strops and materials just so I can learn from somebody with confident experience. I'm usually pretty okay at fine motor tasks requiring precision. I can even pull blood out of a 15 g bird with a 28 g needle. Don't know why I can't figure out the strop though.
I think this topic has been well covered by the posters here.
The edge geometry is what really determines cutting potential.
Any given steel with a good heat treatment can be made very sharp, be it convex or flat bevels.
But the bottom line is a polished edge stays sharp longer, and a convexed edge is what you get by polishing on a strop, even if you start with flat bevels.
As one who used flat bevels for over 30 years, and resisted the convex trend; I can honestly say that I get my best performance out of convex edges.
"If you're not living on the edge, …you're taking up too much space."
Big Mike
The edge geometry is what really determines cutting potential.
Any given steel with a good heat treatment can be made very sharp, be it convex or flat bevels.
But the bottom line is a polished edge stays sharp longer, and a convexed edge is what you get by polishing on a strop, even if you start with flat bevels.
As one who used flat bevels for over 30 years, and resisted the convex trend; I can honestly say that I get my best performance out of convex edges.
"If you're not living on the edge, …you're taking up too much space."
Big Mike
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- May 17, 2006
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The first couple of times I did it this was my result as well. What I started to realize was that I was putting too much pressure on the the blade as I drew it back along the paper. Once you have established a rough convex edge bevel with the 220 grit paper, start laying the blade completely flat on the paper using hardly any pressure. After that primary 220 grit shaping is done, you want the paper to start doing the work. It may seem like it is taking forever, and it most likely will the first time you go through the grits. As I said, lay the blade flat and run through the grits not worrying about the sound as much as seeing the previous grit scratches disappear along the side of the blade. If you roll the blade up onto the edge, and you hear that sound, you have most likely gone to far in lifting the blade and probably rounded off the edge. For your first try, try on something with a full flat ground blade. Something like a SAK. That way, you can use the flat sides in order to see your grit progress. The small blade of the SAK will probably be much easier in order to accomplish this all. Something larger and thicker like a Buck 110 or the like is much more difficult to get the hang of since it has a hollow grind and a much thicker edge initially. Once you get the hang of it you can do pretty much any blade of any size and steel type. I like to tape off the nicer blades that I have when convexing and leave only the last 1/8" - 1/4" (depending on size of blade) of the side closest to the edge untaped. If you do this first with masking tape and then a layer of duct over the top you'll protect the finish of the blade without making it a pain to get off. If you work through the grit this way, once you get to 2000 grit, you can blend the convex in with the original finish leaving a nice pretty transition area. Here's a picture of a big blade I convexed using the tape off method:
See how the polished convex blends in with the lengthwise 600 grit finish. Hope this helps.
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I suppose, in theory, if you put a nice shallow v grind on- say 9 degrees each side and just stropped like mad every time you needed to touch up, you'd have an excellent convex edge in a few months of using. and perfectly matched to your stropping methods.
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I agree. Here are some really rough paint drawings that explain how I see the convex taking shape.
Here is where I see the 220 doing the most work. Basically, we are trying to knock the shoulder off of the v-grind. At this point we are not trying to sharpen the edge as much as we are trying to establish a smooth curve.
If that was done correctly, then all we have to do is run up through the grits using the right amount of pressure and it should sharpen it up real nice. In the drawing, I have left space between the blade and the paper in order to show what shapes they have formed. In reality they are touching obviously and the paper should be just barely touching the edge while we draw backward.
This is what I think happens when you apply too much downward force on the blade as you pull back. It is rounding the edge, but too much. It is making the final edge angle so steep that it isn't an efficient cutter anymore.
I am by no means an expert at any of this but this is kind of what I think is happening. Sometimes it helps in explaining to draw it out.
