Edge Geometry

1

1vertigo1

Joined
Nov 7, 2007
Messages
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I am new to knife making can some one describe edge geometry I see this term come up quite a bit and it certainly peaks my attention.
 
Edge geometry is basically the different shapes a blade's edge area can be in profile. Very acute angles to the edge, or a slim concave edge (hollow grind) for a skinner, or an apple-seed grind / convex edge grind for a chopper for instance. That's my take on it least. :o
 
I've always felt that it's basically a myth that hollow grinds are thinner. You can get much better balances of thin and strong with flat and convex grinds. IMO the only time to use hollow grinds is either for the texture or for straight razors. Convex are my favorite even though I can't do one, most people do them too thick but they can get extremely thin, most Japanese chef's knives are convex ground, which are some of the thinnest blades around. Thin edges cut better than thick edges, and though it is counterintuitive they actually cut longer too. In my opinion you should use the thinnest geometry you can use, as in only use thicker if your use is so rough you will destroy your thin edges. However, thin edges can be surprisingly strong, especially with a tough steel at a relatively high hardness.
 
I've made a convex ground skinner that's pretty nice cutting- it's a full convex grind, not just a convex edge.

So, you have the answer of what geometry *is*, but what you do with edge geometry is a whole other bag of apples.
 
Welcome,
Edge geometry is just the technical term for the shape of the edge. It is how it is applied to a blade that makes of breaks a good knife. Too fat, and the blade never cuts well...too thin, and the edge will chip under heavy use. Just right for the job and you have a knife with proper edge geometry. Machete= fat and convex, razor=thin and hollow. Reverse those edges and neither tool would be of any use. Too fat, and the machete won't cut anything; too thin, and the the razor won't stay sharp through one shave.

Larrin,
I have never seen a Japanese chef's knife with a convex grind, although I am sure there are some. The ones I make (and the ones I have seen that belong to my Korean and Japanese friends) are all chisel ground - flat ground on one side and no bevel on the other at all.
Stacy
 
vertigo (?),

The link posted by SAR describes blade geometry very well, but there does seem to be some overlap of different persons views of the naming conventions. The section titled "Blade grinds" details what is often referred to as "edge geometry"

I did previously try to make a site illustrating the different grinds, but due to peoples different interpretations its not conclusive. you can take a look though if you like:
http://myhome.mweb.co.za/~20022586/grinds.htm it reflects what seems to be the most common interpretations

Lang
 
bladsmth said:
Larrin,
I have never seen a Japanese chef's knife with a convex grind, although I am sure there are some. The ones I make (and the ones I have seen that belong to my Korean and Japanese friends) are all chisel ground - flat ground on one side and no bevel on the other at all.
Stacy
Click to expand...
They do make many chisel ground blades; however, there are just as many (or more) double bevel knives. Either way, they typically grind using a large waterstone wheel, where even flat grinds have some curve to them.
 
bladsmth said:
Larrin,
I have never seen a Japanese chef's knife with a convex grind, although I am sure there are some. The ones I make (and the ones I have seen that belong to my Korean and Japanese friends) are all chisel ground - flat ground on one side and no bevel on the other at all.
Stacy
Click to expand...

I've got one chisel ground usuba hocho- vegetable knife. right handed, of course, which is less than ideal for me.

I've also got two convex ground santokus, one of which I'm restoring.

I'm currently making a couple of convex ground vegetable knives, but I'm not true enough to the particular methods of forging, materials, or shapes to say they are really "japanese"

SOmeday I will make myself a proper (left handed) chisel ground cleaver and see how I feel about it then.
 
First off thank you all for the great information and SAR thank you for serving you have chose a noble profession!!!
I have more questions;
I believe I am at the skill level to achieve a flat grind or a chisel grind, now for the fun stuff. How is the concave and the convex grinds achieved?
 
I personally have a much harder time getting a perfect flat grind than a good convex- I can seemingly take the time to balance the slack belt work and just go. Chisel is mostly easy enough, but if you are doing a really straight edge like a kiridashi I've been working on, it's again a finicky thing.

I'm still fairly inexperienced, but how I do a convex is to carefully put a little distal is, and depending on shape, maybe a bit of flat grind, then I just use slack belt and work from the TIP to the ricasso. If I do it the other way, i mess up the tip.

edge up or edge down depends on the shape of the knife, it's mostly a matter of taking it easy and going slow. I'm on a little baby belt system (HF 1x30 with good Abrasives resource belts and a bunch of hand made modifications) so it's slow going, but that's a good thing. Keep the belts pretty tight, and I work 120 to 320 grit on the machine, then 280 to whatever by hand.

Forging... I can't say I get anything like a good convex with the hammer, but I can lay out the blade to where doing the grind is going to be pretty easy.

Hollow grinding, I'm clueless.
 
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