I am starting to think cutting is more in the geometry than in the apex...

[Squashfan]

Not that you don't have to have sharp apex nor do I want to take away from all of the awesome atom splitting edges I see on here. BTW, I think my apexes are better now than they have ever been. But, I have been doing my own crazy sharpening and I just can't get over how much a thin shoulder and low angle make a difference. Am I crazy? I have a stainless Case Congress that I sharpened at a lower than my usual angle one one blade. It was actually a mistake but it really bore fruit when I was whittling soap. What kind of edge is it, you ask? A low convex. Between 15 and 20 degrees per side at the apex. But right now I am starting it at around 10 degrees and letting my natural hold covex the edge. Not that I have that much rock in my hold but it is hard right now to hold an edge that low. So I redid one of the other blades on the Case but I only got to try it out on one thing today at work. It did very well. Better than usual. I would like to hear what you guys think about edge and shoulder geometry.

 

[james terrio]

Flat or convex, thinner cuts better. It's as simple as that.

 

[Jason B.]

Flat or convex, thinner cuts better. It's as simple as that.

Yep, thin for the win.

 

[singularity35]

Don't all of us know that already?

 

[bgentry]

"Thin is sharp." Totally true. It's why box cutters are made from very thin stock and keep cutting long after the edge no longer feels sharp. I love this video by Ben Dale where he illustrates the point.

[video=youtube;vQKKwojVd28]https://www.youtube.com/watch?v=vQKKwojVd28[/video]

Brian.

 

[Obsessed with Edges]

Flat or convex, thinner cuts better. It's as simple as that.

Yep, thin for the win.

Bingo. I think this is likely the most important rule in cutting.

Not that you don't have to have sharp apex nor do I want to take away from all of the awesome atom splitting edges I see on here. BTW, I think my apexes are better now than they have ever been. But, I have been doing my own crazy sharpening and I just can't get over how much a thin shoulder and low angle make a difference. Am I crazy? I have a stainless Case Congress that I sharpened at a lower than my usual angle one one blade. It was actually a mistake but it really bore fruit when I was whittling soap. What kind of edge is it, you ask? A low convex. Between 15 and 20 degrees per side at the apex. But right now I am starting it at around 10 degrees and letting my natural hold covex the edge. Not that I have that much rock in my hold but it is hard right now to hold an edge that low. So I redid one of the other blades on the Case but I only got to try it out on one thing today at work. It did very well. Better than usual. I would like to hear what you guys think about edge and shoulder geometry.

For shoulders specifically, I'll always like a convexed shoulder better, as there's no hard corner there to wedge or bind up in thicker and tougher material. This makes a big difference on thicker blades especially, if used for cutting heavy cardboard or other such tough material. Going even further, a polished or mirrored convex on a thicker blade makes a huge cutting difference; becomes almost scary-slick in heavy cardboard, as the convexed & shiny shoulders feel almost greased in going through it. Keep the fingers out of the blade's path.


David

 

[BluntCut MetalWorks]

Yes and No and depends.

In term of least energy expenditure per glide through crotch of tall & stiff material, thin geometry is most efficient. Keep simple by ignore steering.

Blade with low friction coefficient good for cutting sticky/grabby/bindy materials - note: mirror blade can be sticky cause by vacumn & or heat.

Ignoring cases where wedging splits material ahead of the apex, e.g. split bamboo/wood with a thick blade/hatchet... Apex width determines whether material will fracture or tear (essentially near apex geometry, wedge to split) or crush. Cutting - by hand - rope/paracord/fiberous materials best use thin/sharp apex. Steering can be issue with tearing.

 

[Twindog]

Geometry cuts, but it's the steel and the heat treat that support that thin, high-performance geometry. And, of course, a lot depends on what we're expecting the knife to do. With wood choppers, you don't usually want thin because the blade will just get wedged into the wood.

Singularity asks a good question: don't we all already know this? But I think not, even on this knife-enthusiasts forum. From previous threads, my sense is that most people on the forum use a 40 degree inclusive edge or thicker. And there is a very strong sentiment that the high-tech steels that can support thinner geometry are just the "flavor of the day." I see blade stocks and geometry running pretty thick on most EDCs.

Most of my EDCs at 30 degrees inclusive run .030 inches or wider behind the edge. My Microtech DOC with the nightmare grind runs 0.080 or thicker behind the belly edge at a 30-degree edge profile.

My Sebenza runs 0.017 inches behind the edge, and then, because of the hollow ground blade, it gets thinner. When you can get edge and blade geometry working together, you can get a high-performance EDC. But I hardly ever see people posting about the Sebenza's blade geometry.

 

[REK Knives]

for most edc tasks (barring batonning and prying) I like a .010" thick edge at 15 dps. It is a slicing machine!

 

[Fred.Rowe]

Thin at the shoulder as well as at the spine. Thin in both places allows for the most sharpness, is that proper? The shape of a razor blade for instance' Not practical for a knife thats used but in theory, the best shape for sharp.

All things being the same, flat is sharper than convex; I've never seen a convex razor blade. Its not the shape at all but the process and technique of freehand sharpening a blade that makes a convex edge so functional. Its not a matter of shape, but a matter of contacting the apex when sharpening.

Sorry for departing in such a huff, I was operating in overload mode, Fred

 

[Squashfan]

Bingo. I think this is likely the most important rule in cutting.

(Snip)

David

I think any knife nut you ask on this forum will say that thinner is better. But I would wager that most peoples won't think about checking their knives or thinning the grind. It just seems to be a simple thing but it is almost completely overlooked. I have more to say but I want to get to a keyboard instead of this tablet...

 

[Obsessed with Edges]

I think any knife nut you ask on this forum will say that thinner is better. But I would wager that most peoples won't think about checking their knives or thinning the grind. It just seems to be a simple thing but it is almost completely overlooked. I have more to say but I want to get to a keyboard instead of this tablet...

I agree. There was a time, not too long ago, when I took it for granted the factory edge or grind was 'right'. After thinning my first edge down to 30° or lower and realizing what 'sharp' really was (epiphany moment), I've never looked back. I've yet to find an edge that didn't perform much, much better in doing so, and it's often the first thing I recommend to someone asking the question, "Why isn't my knife cutting well?"


David

 

[snippy]

I have a Vox Ripley (Boker version) and it is super thick (7mm) and it has a blunt edge. My guess is maybe 50 or 60 degrees inclusive convexed and it is no longer apexed. It will not cut paper or even a plastic bag. It will, however, chop down a tree almost as easily as my BK-9 that I do keep apexed at 40 degrees inclusive.

I'm still learning but this is my experience out in the field. Knives are complex tools that look so simple.

Eric

- edit -

Sorry I am off topic. Cutting and Chopping are two distinct chores as I have just been informed! I should know the difference by now. Also - here is a picture of my ripley (the Blunt Beast). I'm surprised that it doesn't come up in a google search!

Eric

 

[HeavyHanded]

I think any knife nut you ask on this forum will say that thinner is better. But I would wager that most peoples won't think about checking their knives or thinning the grind. It just seems to be a simple thing but it is almost completely overlooked. I have more to say but I want to get to a keyboard instead of this tablet...

In the manual I wrote and illustrated for my Washboard, I tried to touch on a number of general sharpening/edged tool aspects. Thinning the edge comes right after burr removal on the back of page 3....

Fred, nice to see ya back!

 

[Squashfan]

So many good replies! I can't respond to them all! But the bottom line of what I am saying is this. We can sit and talk all day about types of grinds (IE: hollow, saber or FFG.), edge finish (just polished or perfect mirror), and blade steel. But if the knife in question is thick behind the edge, it won't cut well. I am literally just now coming to understand this. For the longest time, the first three things dominated my knife buying. But now I am realizing that they might be one of the last things I should look at.

Couple of quick thoughts:

Say, Bluntcut, what do you mean by steering?

David, I sorta had a double epiphany. I started learning about how much thickness behind the edge matters in Gary Graleys thread on chopping up books. Then , by accident, I added a shallow angle edge to a thin shoulder. That is a knife that is evil "sharp". But it almost all the the geometry of the shoulder and edge grinds.

Martin, I think your Washboard manual is one of the most complete sharpening resources I have seen. There may be something better out there but I haven't yet seen it.

I have been here 30 minutes typing this reply. I wish I had another 30 to type some more!

 

[BluntCut MetalWorks]

Regardless of thin/thick geometry, it will take a Y amt of energy to overcome X degrees of unwanted steering. For example, if you want to make a straight cut through cardboard with a blade has asymmetric grind (intentional or inadvertent), well time to borrow the hulk's arm & wrist.

Similarly, tearing (from blade wedge or crushed by dull/fat apex) occurs instead of cut/fracture the material, tear direction is mostly random downward, thus the apex favor/lean toward path of least resistance (tear path). Again, it take energy to overcome this unwanted steering. Implied, when apex wider than certain width, crush/tear taken place, hence won't 'cut' well.

Say, Bluntcut, what do you mean by steering?

Too thin and flat bevel can create nasty stiction (food/material stick to blade). Hollow grind helps. Thin but with some convex cutting bevel also lessen stiction. Depend on target cutting material, key is to get the right amt of wedge to stretch material then the apex has an easier job fracture 'stretched' material, and then continue wedge material away from stick to the blade. See ... hahaha, this tastes best when add a pinch of combinatorial optimization.

 

[David Martin]

Yes, correct edge geometry plays a big role in how well a knife cuts. Even when it isn't so sharp. DM

 

[Squashfan]

Regardless of thin/thick geometry, it will take a Y amt of energy to overcome X degrees of unwanted steering. For example, if you want to make a straight cut through cardboard with a blade has asymmetric grind (intentional or inadvertent), well time to borrow the hulk's arm & wrist.

Similarly, tearing (from blade wedge or crushed by dull/fat apex) occurs instead of cut/fracture the material, tear direction is mostly random downward, thus the apex favor/lean toward path of least resistance (tear path). Again, it take energy to overcome this unwanted steering. Implied, when apex wider than certain width, crush/tear taken place, hence won't 'cut' well.



Too thin and flat bevel can create nasty stiction (food/material stick to blade). Hollow grind helps. Thin but with some convex cutting bevel also lessen stiction. Depend on target cutting material, key is to get the right amt of wedge to stretch material then the apex has an easier job fracture 'stretched' material, and then continue wedge material away from stick to the blade. See ... hahaha, this tastes best when add a pinch of combinatorial optimization.

Okay! That makes sense. Wouldn't that also be a problem when carving something hard like wood?

EDIT: Oh and welcome back Fred!

 

[james terrio]

I agree. There was a time, not too long ago, when I took it for granted the factory edge or grind was 'right'.

Factory edges and grinds - despite what the marketing people will tell you - generally have a lot more to do with whatever is trendy, ease of manufacture and leaving a bit more steel for the sake of overall strength than they do with performance. Manufacturers are in the business of moving lots of product with a decent profit margin, not cutting things

 

[Obsessed with Edges]

Factory edges and grinds - despite what the marketing people will tell you - generally have a lot more to do with whatever is trendy, ease of manufacture and leaving a bit more steel for the sake of overall strength than they do with performance. Manufacturers are in the business of moving lots of product with a decent profit margin, not cutting things

Agreed. I went ~20 years or more in being (somewhat reluctantly) satisfied with what a given manufacturer gave me in an edge. This is why I don't doubt at all, that most casual users of knives will never know of, or care about, what they're missing in a typical factory edge. I'm sure most consumer-grade knife manufacturers know this as well, and are perfectly happy with it; it's easier and cheaper for them, this way.


David