Advantages of a convex grind???

J

JSR

Joined
Apr 4, 2006
Messages
338
I'm trying to decide on a new Santoku for the kitchen. One of the ones I'm considering has a convex edge. I've read the how-to's to sharpen a convex edge, but if possible, I'd prefer not to have to do so. The main reason I am considering the Santoku with the convex edge is because it seems to have the most comfortable handle and is lower priced than the others I'm considering.

I'm wondering what the advantages are of a convex edge, particularly for food prep, mostly slicing? If the advantages are minimal, I'll either drop the knife from consideration or change the edge to a flat grind on my sharpmaker when it's time to sharpen. If there's some very good advantages, I may consider using the mouse-pad technique for just this knife, but I'd prefer not to.

Thanks.
 
There is only one theoretical advantage to a convex edge and that is the elimination of a sharp bevel transition reducing friction and some would contest even that advantage (though I firmly believe that it often make a difference).

However in practice there is often a very noticable practical advantage to convex grinds which is that they are ground to zero edge and have essentially knocked off a lot of the width behind the edge. If you measure a BRKT for example it turns out that the terminal edge angle is around 13 deg and at a comparable hight from the edge (were on most knives the bevel shoulder would be) the blade is significantly thinner regardless of how thick the blade eventually gets (spine thickness). That is an edge geometry that puts a Spyderco factory edge to shame and that is saying something for a factory edge (not that you couldn't do better yourself, of course). Now this has not necessarily anything to do with the convex shape but it is not uncommon to find this advantage on a convex ground blade. For choppers there is a different advantage, as a convex edge is essentially an infinite series of microbevels, strengthening the edge while keeping a reasonably thin blade profile. The limited contact area is also reducing binding. But none of that is likely going to make any difference on a kitchen knife.

For resharpening, there is really no reason to fear a convex edge. Using the Sharpmaker is really no problem, as long as you aren't using it too aggressively, you won't change the profile appreciably. If you have a bit more work to do, you can maintain the profile with a mousepad and to the final edge with the Sharpmaker again.
 
I use a few Bark River knives in the kitchen and stropping keeps the edges keen. I have even been able to use the Rogue bowie, a large heavy knife, for fine slicing. I have a lot of confidence in that convex edge.

If you don't get a Japanese knife with a convex edge, would you look for a chisel grind, and if so, how would you sharpen that?
 
I agree with Esav. I had a chisel grind dive knife - blech. Okay at first but when it became dull it was dull. I ended up reprofiling it to a flat ground with much effort.
 
Actually, some of the world's sharpest kitchen knives are chisel-ground Japanese knives. But maintenance of that edge takes some expertise. Of course, they are used in a very specific manner. A dive knife needs to be versatile.
 
I have found the convex edge on my Bark River Mini Canadian to be super quick and easy to sharpen with 1000 and 2000 grit sandpaper on top of a thick piece of cardboard after I messed it up by accidentally banging it edge first on a stone hearth (and I suck at sharpening knives). Simple stropping works the rest of the time.
 
HoB said:
If you measure a BRKT for example it turns out that the terminal edge angle is around 13 deg and at a comparable hight from the edge (were on most knives the bevel shoulder would be) the blade is significantly thinner regardless of how thick the blade eventually gets (spine thickness). That is an edge geometry that puts a Spyderco factory edge to shame and that is saying something for a factory edge...
Click to expand...

There are Spyderco's with full flat grinds down to 0.005" or so with ten degree or less apex bevels.

-Cliff
 
This may be a little off of the current argument, and I don't intend to hijack... If you like the feel of the knife and the steel it's made of, there is no rule saying that you have to keep it convex. The first time that I sharpen most of my knives, I end up reprofiling anyway. You can always buy the convex and then sharpen it as you would any other knife. You would lose some the the discussed advantages of the convex grind, but you would have a knife you like.
 
With the very thin convex grinds with most kitchen knives, you can sharpen normally if you wish, or you can explore one of the many methods to sharpen a convex edge.
 
Cliff Stamp said:
There are Spyderco's with full flat grinds down to 0.005" or so with ten degree or less apex bevels.

-Cliff
Click to expand...

If there are, I haven't seen any. Quite frankly, I very much doubt that there are any. Please read my post carefully: I was talking about FACTORY EDGES and was very clear about that. Not about what Krein might put on a Spydie. Please be specific which models you are talking about because I have handled a few. Thinnest I've seen was the ZDPCaly jr. which was about 12 deg per side and 0.013" behind the edge and that stood out from the rest. Even the regular gray VG-10 Caly Jr. was thicker. It is also a pretty thin blade stock. Do you want some numbers on the factory edge of a 4mm stock Spydie like my Lil'T or Manix? More like 0.025-0.03+" behind the edge and 15-17 deg per side and being a Spyderco fan myself, I don't say that to ditch Spyderco, because I think they were still pretty good edges. Not to mention that according to Spyderco the blade are sharpened at about 15 deg per side (give or take a couple), while according to Mike Steward BRKT aimes for a terminal angle of 13 deg per side.

I am saying this to show how unevenly you portray knifes of different companies lately. Now you want to compare a custom ground Spydie to a factory edge BRKT which only obscures the issue. I really begin to wonder why?

Neeman: The edge or entire blade has the profile of an apple seed.

Edit: As I continue to think about this, maybe Spyderco grinds their kitchen knives that way, I don't know, I've not held a Spyderco kitchen knife nor have I held a BRKT kitchen knife, if they are even out yet.
 
pablo486 said:
This may be a little off of the current argument, and I don't intend to hijack... If you like the feel of the knife and the steel it's made of, there is no rule saying that you have to keep it convex. The first time that I sharpen most of my knives, I end up reprofiling anyway. You can always buy the convex and then sharpen it as you would any other knife. You would lose some the the discussed advantages of the convex grind, but you would have a knife you like.
Click to expand...

Pablo I'm just curious what knives have you done this to and how it turns out. It sounds like exactly the kind of thing I would do but haven't yet.
 
HoB said:
I was talking about FACTORY EDGES
Click to expand...

So was I, edges of 0.010/10 degrees are not uncommon, even on the larger models like the Temperance.

Do you want some numbers on the factory edge of a 4mm stock Spydie like my Lil'T or Manix? More like 0.025-0.03+" behind the edge and 15-17 deg per side...
Click to expand...

Well yeah, you would expect that on knives like the Paramilitary, Manix and such the edges would be thicker and more obtuse. My Manix was still though 0.020-0.025"/10-12 degrees, still under the Bark River apex.

My point was simply that there is nothing inhernetly thin about a convex grind and you can get flat grinds which are far more acute in apex and primary bevels, production or otherwise. Krein is also hollow, not flat on his regrinds.

-Cliff
 
I essentially defer to Cliff on matters of sharp, but I should add that "hollow" and "convex" are relative terms.

The performance of a hollow grind is largely dependent on wheel diameter, combined, of course, with width of the blade. The same is true of convex grinds. Does the convexity begin from the spine, or does it begin very close to the edge off of an essentially flat grind? And, finally, how thick is the blade 0.02 and 0.05" back from the edge (these are somewhat random dimensions, but they are used by Dan Farr in his recent Blade article, and I believe that Fogg and Fikes also use the 0.05" back 1/4" from the edge as a measure of generally appropriate thickness)?
John
 
John Frankl said:
...I believe that Fogg and Fikes also use the 0.05" back 1/4" from the edge as a measure of generally appropriate thickness
Click to expand...

This depends a lot on the knife of course, but it very useful in general to talk about geometry. I have knives that are 0.020" or so at 1/4" back, but you would not do chopping and such as Fikes does in the DVD with them.

-Cliff
 
kgd said:
Pablo I'm just curious what knives have you done this to and how it turns out. It sounds like exactly the kind of thing I would do but haven't yet.
Click to expand...

I've only done it with a paring knife that I got used. It was pretty beat up, so i'm not sure that it compares directly with your experience. Basically, if you've ever reprofiled the primary grind of a knife to a lower angle, you have all the skills that you need. Choose your angle and go untill you feel a burr.

Have you ever reprofiled before?
 
John Frankl said:
I essentially defer to Cliff on matters of sharp, but I should add that "hollow" and "convex" are relative terms.
John
Click to expand...

Correct me if I'm wrong, but I think these terms are a little confused. You can have a hollow ground knife with a convex edge. The convex portion of the blade is only the edge, not the entire blade.
 
You must log in or register to reply here.
Back
Top