Disadvantages to convex grind?

Magic is only in the mind.

I certainly appreciate the described convenience of a sharpening jig. I just never used one.

If it were needed, diamond sandpaper is widely available, as is aluminum oxide (ruby) sandpaper.

I am not sure why so many discussions here get so tense.
 
DeadboxHero said:
The biggest disadvantage? They take more time to sharpen the a regular secondary bevel.
Click to expand...

This is exactly what I came here to say. Furthermore, a fully convexed blade is even more work to establish and maintain than one with a convex secondary bevel. In my experience, eliminating the shoulder where the primary and secondary bevels meet improves performance significantly in harder media.
 
HwangJino said:
Nice work!
Im thinking it's my skills that are lacking.

I'm probably better at convex on kitchen knives than wood working. Here's what my convex usually looks like.
Click to expand...

That's a good looking convex edge. Carbon steel Petty knife?
 
Thomas Linton said:
Magic is only in the mind.

I certainly appreciate the described convenience of a sharpening jig. I just never used one.

If it were needed, diamond sandpaper is widely available, as is aluminum oxide (ruby) sandpaper.

I am not sure why so many discussions here get so tense.
Click to expand...

The tension is a result of your first statement. I thin the shoulders of my flat/flat grinds into flat/convex grinds just like chiral.golem expounds. That works great, cuts like nobody's business, and is easy to maintain freehand.

But! It does not give them magical powers that transcend the laws of physics and geometry, despite what one noted maker of flat primary/convexed edge knives claims.

I love/prefer a convex edge, but blind cultism for them is silly.
 
I love a good convex edge for a lot of tasks.

I find them easy to maintain, and keep sharp.

I've had my share of convex edges that were too thick.

Making an edge convex does not make it stronger or weaker.

They can be obtuse or acute.

You can get them sharp enough to whittle free hainging hair.

This can also be done with v edges.

I do both. I find that on some of my knives, I just keep a regular edge, sharpened on stones and maintained on ceramic sticks.

I find this method to be a bit quicker than pulling out my sandpaper sharpening supplies (a few licks on a diamond atone followed by a few per side on a ceramic is faster and quicker).

But to simply maintain a convex it is a few strokes on a strop per side.

It is when I need to restore an edge a bit after more use, and I need to get the sandpaper kit out, it is a bit more work, and mess. This is so because I use sheets of automotive sandpaper on a firm rubber strike pad (from Tandy Leather).

Lately though, on some of my convex edges I have just been maintaining them on the same diamond stone and ceramic, followed by a few strokes per side on the strop. By doing a few strokes every time at a shallower angles, you can keep them convex this way too without too much trouble.
 
that's pretty similar to what i have to do with my turning tools. some of them do need to be v edged to precise degrees(theoretically-these change depending on your source) because they are compound bevels. i do most sharpening freehand, followed by some stropping-i even have a leather apron i keep a little compound on for touch ups where i don't need a stone(diamond or white transparent slip stone). doing what i do for a hobby i learned early to have to sharpen both ways and blend them or not when appropriate. you can get hair thin curls with each grind, it just depends on technique more than anything(or practice,sigh). learn both and you'll never be disappointed. in all your free time op:) and get the ko wkst they are fast.
 
If you want nice uniform slices, the single bevel (chisel edge) works best. Think sushi.
If you need to change directions as you cut, a convex edge works best. Think pumpkin carving.
If you can't decide, the double bevel is the modified limited hang out.
 
On high quality kitchen knives there are very few exceptions to (mostly complex) convex grinds and those are special-grind knives like single bevel knives or honesuki knives (which mostly have one side completely flat). It allows the knife makers to tune the knife's cutting properties. Yes - it takes some experience in hand free sharpening to maintain the geometry over longer period of time.

Concave grinds tend to get stuck in food and can not be properly maintained over time. Flat grinds tend to stick to food. On top of that a knife with 1-2 inch wide blade can not have a fully flat grind as the knife would be way too thick at the spine, or it would have way too thin edge. Some so called wide bevel knives may have these wide bevels (about 1cm wide, give or take) completely flat, but usually these are also more or less convex.

I have frankly hard time to see much reason for concave grinds with modern utility knives other than ease of production (though I may be admittedly wrong here). It also allows for a knife that is usably thin behind the edge, but thick(strong) at the spine what may (but rarely does) have an advantage in usability, but allows for more freedom in design. From pure utility point of view I would consider convex or flat grind most useful and possible to maintain over long time (as long as you are not scared to scratch that nice stonewashed finished).

Yeah, I am a rather kichen-knife-centric person :)
 
matus said:
Yes - it takes some experience in hand free sharpening to maintain the geometry over longer period of time.
Click to expand...

OMG, didn't realize there was such a thing!

JK, I get exactly what you are saying. I just got one of these: http://www.bladeforums.com/forums/s...-6-quot-Kitchen-Utility-Vegetable-Knives-SOLD

It is by far the best knife I have ever used, kitchen or otherwise. Granted, I wouldn't smash it through wood, escape a crashed helicopter using it, or cut through hundreds of boxes wrapped in tape with it because that would make it yucky looking; but the thing is damn perfect in the kitchen!
 
Last edited:
craytab said:
Yup. It is funny when the one who starts the tension complains about it :thumbup:
Click to expand...

Well, I didn't mean to imply that Thomas Linton's statement caused the tension, I meant to imply that his first statement nailed the cause of the tension whenever the convex topic comes up.

People believe convex grinds have magical powers, and they get all bent outta shape, hunker down, and release the hounds when you tell them they don't. Even if you draw a simple picture demonstrating that fact.
 
Last edited:
I stated the san mai III trail master "cuts like magic", not "chops". It's just an expression . A full convex blade grind will tend to bind in the material it's chopping.
There's a big difference between a convex edge grind, and a convex blade grind. A convex edge grind on a flat or hollow blade grind will out-chop a convex blade
grind.
 
Last edited:
marcinek said:
Well, I didn't mean to imply that Thomas Linton's statement caused the tension
Click to expand...

My mistake. I was referring to his second statement where he touted someone with 60 years experience of sharpening as if it where the end all beat all. The tired vague argument of I know more because I or someone has many more years of experience is just what appears, tired and old.

Counter to what he said, anyone can learn to hold an angle and properly sharpen a V grind without making it convex. It takes practice, control, and diligence. But you sure don't need 60 years experience to achieve those things.
 
Except for hewing axes, axes are traditionally full convex ground in on this side of the Pond. Same for khukuri and bolos. Not magic. Just chops better because the blade is less likely to bind in the work.

This is exaggerated, but makes the point.


Axe gauge, U.S.F.S.

 
Last edited:
matus said:
Then here is your redemption - the best videos on free hand sharpening there are by Jon Broida.
Click to expand...

Then you didn't see the joke in your post:

matus said:
Yes - it takes some experience in hand free sharpening to maintain the geometry over longer period of time.
Click to expand...

You know....Hand free.....? Get it?

It's just a goof man. I know how to hand sharpen, quite well enough for my needs.
 
matus said:
Concave grinds tend to get stuck in food and can not be properly maintained over time.
Click to expand...

Sure they can. You just need a grinding wheel or scythe stones to do it. You use the curved edge of the stone to follow the hollow. It's just common, depending on the specific hollow grind, for the radius of the hollow to increase because most grinding wheels and scythe stones feature a larger radius to them than the wheels that were used to produce the original hollow. That's not necessarily a bad thing, though, as it reduces the binding problem.
 
You must log in or register to reply here.
Back
Top