convex edges

[koyote]

Every once in a while there's a thread about convex edges, and usually Scott and I chime in from our respective viewpoints, but there are aspects that seem to not get discussed much.

For example, I often have to explain the 3 types of convex edges I do after the fact- there's the full convex from the spine- a really elegant blade grind for thicker steel that's a very solid performer and my favorite for a heavy blade:

There's the convex final bevel- usually if I'm doing one- I'm doing it on a saber grind:

and the one I find hardest to describe, the 'scandi' style convex taper.

or

This one is hard to describe! it's not a saber grind, not a full convex, and not a scandi.



The other thing that seems to miss discussion a lot is one of the primary benefits of a convex edge - especially on large knives. A traditional leuku will often use the pattern where the very base of the blade has a steeper angle for power cuts, thinning out to the belly and thickening to a more obtuse angle again at the very tip. I have my own variation on this, and anyone who "gets into" convex edges can and should learn their preferred technique and angle variation.

I know we've all seen KSAs and other Survival Tools that have the very highly defined, sharply (as in fracture point) differentiated grind regions. I think the convex has the best organic flow to doing this and that the end result is a stronger and more adaptable blade.

 

[Diomedes Industries]

This is a great thread Christof!

I prefer the full convex - but that is my cutting style. Offering all three gives the user the option to match the grind to what they want out of the knife.

TF

 

[Big Mike]

Good topic Christof, I think you are correct in that a lot of people don’t understand the intricacies of the convex blade.

Full height and high convex (as seen on many Bark River products) are probably what most folks think about.

But like you make, the convex saber style (or convex Scandi style, if you will) is a great performer on thinner steel.

Convex edge grinds can be used on any grind style, I have done them on flat ground as well as hollow ground blades.

I have even seen them on full height convex grinds where a thicker edge is desired then you would get from a zero degree edge created by the primary bevel (think dedicated chopper), they are less apparent then most secondary bevels.

Also, as you say, a thinner geometry near the handle and a thicker edge out toward the sweet spot on a chopper is easily accomplished without sacrificing the clean lines of the grind.

Convex grinds are my favorite, and have been the grind of choice throughout the history of the knife; flat and hollow grinds being the result of the industrial revolution.




Big Mike

”Scaring the tree huggers.”

Forest & Stream

 

[Rick Marchand]

I have been loving the (almost) full flat with a secondary convex... by far, my best performing knives. I do most of my final convexing on stones now and won't go back to a mouse pad for sharpening. You can really control the curvature of the convex bevel on a stone. I like low approach angles on my final cutting edge.

 

[Diomedes Industries]

Can you show that blade (or a similar one) from the edge first - so that I can see the profile?

A tutorial on stones (convexing) would be awesome Rick.

TF

 

[cybrok]

+1

The mousepad technique works, but it's so long.

 

[Rick Marchand]

I'll try to put a tutorial together... Thanks

this is the best I can do for the edge pics...

And here is my stone set up...

 

[Big Mike]

I never liked the mousepad thing to create a convex edge.

I could see if they’re not too soft they can be used to maintain a convex edge, but I prefer sandpaper over a thick piece of leather.


I have used stones in the past to create a convex edge, as has been done for centuries.


Personally I have been spoiled by a slack belt grinder with fairly flexible belts; I find that by varying the pressure applied and belt tension I can get the results I’m looking for.




Big Mike

”Scaring the tree huggers.”

Forest & Stream

 

[Stickman]

Great post guys. I'm not a knife maker, but I've never met a production blade that was as uniform and symmetrical as I like, so I guess I'm a dedicated knife modifier. I'm glad to see Rick mention the use of stones for convexing, at least for the final curvature, as he's working with full flat grinds. I like this method also and for the same reasons...I think the mouse pad method is way too soft for anything other than a quick touch-up. I find hard leather strops with a hard base material work best for the flatter convex profile I like to use. That probably explains why I also found that convexing on the stones or wet and dry on glass to provide more control and accuracy. Once I get the profile I want then I use the hard strops (hones) through the final finishing steps.

 

[tidefan]

Okay..I know I'm a dork for asking, but do convex edges hold an edge better/longer than beveled edges. I grew up using arkaansas stones and norton stones on case xx pocket knives and buck fixed blades. I just got a Barkniven S1 with elder burl scales and a convex grind. It seems I'll have to re-learn how to sharpen and maintain the edge. Is it worth it?

 

[koyote]

I do the full convex grinds with a slight decrease in radius on the bottom third to make sharpening more sane.

In any case, I do most of my sharpening and maintaining with a strop, occasionally hitting a stone or ceramic rod. These days on really heavy use knives (like the kitchen knives the teenagers chop into the steel counter on "accident") I will touch up the edge with an 800 grit slack belt and then strop.


I mostly put convex edges on with a slack belt, but that's in no way necessary to maintaining them.

I think Rick is a bit more professional with his stones than I , but I highly recommend for people who want variable angle convex edges- especially the convex scandi I do, get a ceramic stick.

 

[dawsonbob]

I really like those not-a-scandi-convex jobs (nice looking leather, too). Clean looking work.

 

[Fiddleback]

I do full height convex grinds with a convex microbevel.

 

[BarberFobic1992]

Good thoughts christof, convex is a pretty broad term that needed a little clarifycation.

Oh, and +1 on thick leather instead of mousepad. the leather keeps it from getting too obtuse.

 

[Jason B.]

Okay..I know I'm a dork for asking, but do convex edges hold an edge better/longer than beveled edges. I grew up using arkaansas stones and norton stones on case xx pocket knives and buck fixed blades. I just got a Barkniven S1 with elder burl scales and a convex grind. It seems I'll have to re-learn how to sharpen and maintain the edge. Is it worth it?

Very worth it, convex in any form improves cutting performance and edge durability.

One of the best examples of I convex blade I have used has been the Bravo 2, it has a nice high saber convex and cuts like a sword.

My favorites are the one's I do though simply because I can control the amount of convex for the specific blade. My JK knives were full convex with a secondary bevel I'm guessing for ease of sharpening but I like mine to have a zero bevel. A little time with a beltsander some sandpaper and a strop and I got them how I like'em.

JK-AK, thicker for more durability. Blade standing on its spine looking at the tip.

JK hiker, thin for good slicing.

 

[kgd]

All this knocking of the mousepad method Yeah its not really that great to put your final edge on, but where the mousepad seems to excel (for me) is converting a V-grind to convex edge which is how very many of us get exposed to convex edges. I still have a soft spot in my heart for the mousepad method. I agree that it doesn't really get your knife fully sharpened.

After putting a convex edge on it, I take it to the strop. Most times though I convex as sharp as I can by mousepad/sandpaper and then put a little microbevel on there with the sharpmaker with the 20o angles making. It is just so much faster (for me) to do it this way than stropping to the desired edge. Stropping takes me another 15 min or so while the micro-bevel is about 30 s.

I'm interested in learning better technique with the stones and also getting a little belt grinder to play around with.

 

[milani74]

Sharpening convex is confusing to me because of the angle. I am thinking of getting a belt sander from Harbor Freight and playing around on some cheap knives.

 

[mtnfolk mike]

great thread indeed Kristof...:thumbup:

i'm with Rick on this one.. i tend to prefer a full flat with a secondary convex edge.. it seems to work the best for me and is fairly easy to maintain...

I have been loving the (almost) full flat with a secondary convex... by far, my best performing knives. I do most of my final convexing on stones now and won't go back to a mouse pad for sharpening. You can really control the curvature of the convex bevel on a stone. I like low approach angles on my final cutting edge.

 

[koyote]

All this knocking of the mousepad method Yeah its not really that great to put your final edge on, but where the mousepad seems to excel (for me) is converting a V-grind to convex edge which is how very many of us get exposed to convex edges. I still have a soft spot in my heart for the mousepad method. I agree that it doesn't really get your knife fully sharpened.

I'm not knocking the mousepad so much as all that- I do think it's a really good tool for the convex final bevels or microbevels.

 

[Rick Marchand]

I'm not knocking the mousepad so much as all that- I do think it's a really good tool for the convex final bevels or microbevels.

As long as you don't push too hard or raise the spine. Both are edge killers.