convex edge?

T

Tomso

Joined
Mar 29, 2006
Messages
336
What is so special about convex edge? Why do everybody like it so much...holds edge longer, slices better? I know its pretty hard to sharpen a convex edge, so i guess there must be something about it, that makes people go through all that trouble of re profiling.
 
I've used egded tools for a long time in woodworking. Some tools get a convex edge that require a stronger edge due to the pounding the tool takes. You get more meat behind the edge with this type grind. But cutting efficiency I think is a little reduced from the other grind I use which is a hollow grind. Hollow grinding results in a thinner cutting edge which is easier to control and has a little less resistance because there is nothing really behind the cutting edge. But then this grind is weaker because of less support behind the edge. I think the happy compromise is what we do in our knives which is a flat grind on the blade with a small secondary bevel as the cutting edge. You get the thinner sharp edge and still have a little support behind it without the fat convex curve sticking out there in the way of the cut. I know this is gonna generate some opposite responses because there are a lot of convex followers out there. But this has been my experience:)
 
Thanks for explaining, guys. I will try it and see how it goes...Although mouse pad isnt something i take with me when i go nature hunting. Doesn't that limit you a bit if you need to resharpen it in the woods or somewhere like that? How do you guys sharpen you convex edge outside?
 
Tomso said:
Thanks for explaining, guys. I will try it and see how it goes...Although mouse pad isnt something i take with me when i go nature hunting. Doesn't that limit you a bit if you need to resharpen it in the woods or somewhere like that? How do you guys sharpen you convex edge outside?
Click to expand...

You can make your own leather strop hones using some left over 1/4" leather and a wooden paint mixing stick. Cut the stick to the length you find easy to carry and then trim your leather to fit and glue it on. After that you can take pieces of sandpaper with you and just wrap it around the hone when needed.

Hopefully I made that clear, and if not maybe someone else will jump in with something better. There are many knowledgeable persons in the RAT Forum.
 
If you'll be outdoors for a while just pack a small leather hone or strop. Basically a slab of wood with compound coated leather on both sides. Just touch it up on the leather at the end of the day to keep your edge keen. A small sheet (or sheets) of sandpaper can be laid down right on the leather if your edge needs a little more work. Derrick over at KSF has some great kits with everything you need in an Otterbox. But you can put a similar set together yourself pretty easily. I use my strop on all my knives, with both convex and beveled edges.
 
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I have found all three edges useful, but sometimes I think too much is made of the type. For wood carving a narrow angle bevel or even hollow ground edge works well. For chopping, I find that a nice convex edge penetrates deep and holds up well. Falkniven and Bark River use convex edges and even full convex grinds a lot. A lot of bushcrafters like the Scandinavian flat grind, which is usually a very narrow angle bevel on an already thin blade. The thinner the blade, the narrower the angle can be, like a razor blade. They all work well enough. Sharp is sharp.
 
Horn Dog said:
I have found all three edges useful, but sometimes I think too much is made of the type. For wood carving a narrow angle bevel or even hollow ground edge works well. For chopping, I find that a nice convex edge penetrates deep and holds up well. Falkniven and Bark River use convex edges and even full convex grinds a lot. A lot of bushcrafters like the Scandinavian flat grind, which is usually a very narrow angle bevel on an already thin blade. The thinner the blade, the narrower the angle can be, like a razor blade. They all work well enough. Sharp is sharp.
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+1

I like that statement, sharp is sharp!

I prefer freehand sharpening on large bench stones. Starting course and working my way up to a final hone with a translucent Arkansas. I then finish the edge by stopping to get it hair splitting/popping sharp.

I've never had any problems at all with cutting ability with my knifes sharpened this way. I don't see any need to reprofile them to a convex shape.

I think the final edge angle you sharpen to makes a much bigger difference than whether it is achieved with a flat, convex grind, or a combination of both.
 
Tomso said:
Thanks for explaining, guys. I will try it and see how it goes...Although mouse pad isnt something i take with me when i go nature hunting. Doesn't that limit you a bit if you need to resharpen it in the woods or somewhere like that? How do you guys sharpen you convex edge outside?
Click to expand...

You can also just lay some sandpaper on your thigh and sharpen while sitting around the campfire if it needs more than a stropping.

RC-4 with convex
DSCN1239.jpg
 
Nice edge. My convexed recurve RC-4 cuts well, too, but not as well as a razor thin Mora.
RC-5026.jpg
 
I love convex edges. I find them to cut very well and hold a edge well. I also find them to be by far the easiest to sharpen.
 
My other RCs still have the factory bevels. I have been using some other blades of exotic and harder to sharpen steel. It was relaxing and refreshing to just give those RATs a few light strokes with a ceramic rod and bring them back to shaving sharp. God Bless 1095 steel.
 
MikePerrin said:
I've used egded tools for a long time in woodworking. Some tools get a convex edge that require a stronger edge due to the pounding the tool takes. You get more meat behind the edge with this type grind. But cutting efficiency I think is a little reduced from the other grind I use which is a hollow grind. Hollow grinding results in a thinner cutting edge which is easier to control and has a little less resistance because there is nothing really behind the cutting edge. But then this grind is weaker because of less support behind the edge. I think the happy compromise is what we do in our knives which is a flat grind on the blade with a small secondary bevel as the cutting edge. You get the thinner sharp edge and still have a little support behind it without the fat convex curve sticking out there in the way of the cut. I know this is gonna generate some opposite responses because there are a lot of convex followers out there. But this has been my experience:)
Click to expand...

My understanding is that hollow grinds are the easiest to maintain. The inward concave of a hollow grind means easy sharpening, but like you say above, also less metal behind the edge.

Now with respect to full flat grind versus convex, I think you are right in your statments about comparing a full convex blade like a bark river versus a full flat. In the end, it amounts to how sharp the angle is at the edge. A full convex blade is going to get thicker more quickly for the same edge angle compared to a full flat plus v-grind. Consider the sabre grind of the RC-5...well a full convex is like having several bevels rather than just 2 as in the case of the sabre grind.

On the other hand, what most people are talking about is converting the RC blades from full flat + v-grind edge to a full flat + convex edge. This is ways going to yield a more acute edge because you are converting the factory set edge to convex. You do this by knocking off the shoulders of the secondary bevels. In theory this removes a couple of contact points and improves the slice. No matter what, in converting the knife by this process the main thing to consider is that you are removing metal. Removing metal is making the bevel shoulders more acute and possibly slightly altering the edge itself.

At what point does removing metal start to decrease robustness? I think this is the inherent advantage of the convex conversion. I think if your conversion technique only knocks off those shoulders, then you get better slicing ability with relatively little effect on edge robustness. Also the process tends to smooth out the coating at the bevel/blade junction which further helps reduce friction. On the other hand, I think if you were going to sharpen an RC-4 by converting the primary bevel from 20 degree to 15 degree you would see a drop in the robustness of the edge. So in my mind, the convex conversion provides a happy medium - maximize edge toughness while increasing cutting performance over the factory edge.
 
I love convex knives. All of the V grind knives I have have been reprofiled.

With a leather hone and good quality compound, I can maintain any knife I have. I do it just like the vids on my website.

There is no rocket science behind making the strop and the sand paper is available at any auto parts store.
 
kgd said:
...On the other hand, what most people are talking about is converting the RC blades from full flat + v-grind edge to a full flat + convex edge. This is ways going to yield a more acute edge because you are converting the factory set edge to convex. You do this by knocking off the shoulders of the secondary bevels. In theory this removes a couple of contact points and improves the slice. No matter what, in converting the knife by this process the main thing to consider is that you are removing metal. Removing metal is making the bevel shoulders more acute and possibly slightly altering the edge itself....
Click to expand...

When do finally put my RATs to the Kalamazoo, that is exactly what I will do. While my RATs all came with decent bevel edges, they will eventually have convex edges. I have done this on dozens of heavy duty field knives like Rangers, Busses, Beckers, and others. It always improves cutting. Since I don't chop concrete blocks or pipes, the edges have all held up very well. Even my machetes have convex edges. Besides, it's a hassle to bolt the platen back on anyway. :D
 
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