edge geometry

[Natlek]

Every knife has its use, from filet knives to survival knives, and realistic expectations must be had. There has been a trend lately towards heavier, thicker "survival" knives and on that type of knife the public's perception is that thicker and heavier is better, no matter the cost. What the general public doesn't understand is how much difference proper geometry, steel composition, and heat treatment can make to make a job easier, therefore it doesn't sell. Like FortyTwoBlades said, why spend money on something that doesn't help the product move?

FWIW, Buck is known for doing a ton of research on their blade geometry. They use higher end steels on their limited run knives and even their 420HC is no slouch. Very underrated company IMO.

The thing I don't understand at all is these ridiculously thick folding knives that certain companies sell. I love how good locks are getting, and I think strong locks are a great idea, but even the strongest locks will still break before the average blade. They are only hurting their own performance by making the blades so thick they smash rather than slice. In my mind if you need something really strong for chopping and prying, a fixed blade (or the proper tool) is the way to go.

What the general public do is they buy a knife and used it . Without be bothered about the angle and geometry and which steel ............ for most of general public the knife is just a knife and it is important to have one on hand when needed one .....and when they feel that knife do not cut well , the first stone was good

 

[pinnah]

What is a sabre hollow grind?

It is not that simple...

For chopping wood in the field, what I've found is, if the steel is good quality, a sabre hollow grind blade will tolerate much thinner angles while chopping, while a Full Flat Grind blade will require a thicker more open angle edge.

With a Sabre Hollow Grind, the edge angle can be as low as 12 degrees per side on a 0.020" edge base, and it will tolerate chopping all day long. (Such as a Randall Model 12)

For a Full Flat Grind knife, the edge angle will have to go up to at least 15 degrees per side, preferably sitting on a 0.030" base. Even that is borderline...

(This would not apply to a fully convexed chopper like the SM III Trailmaster or the Fallkniven Thor, because they are not true "Full Flat Grinds". I have found the SM III Trailmaster to be so thickened by the overall convexing that it performed extremely poorly: On these knives, achieving a 15 degree per side final angle is impossible or unlikely anyway, because of their overall "swelled" thickness.)

There are multiple reasons for this particular superiority of Sabre Hollow Grinds, one of the less obvious factors being that wood left on the ground, in the wild, will often "soften" on the outside and "harden" on the inside, creating a medium that will allow more aggressive lateral loads which are more concentrated on the edge itself.

This is because the softer outer will offer less support and allow more accidental twisting movements when unsticking the edge, while the harder inner core will trap the edge more forcefully in a more concentrated manner, often leading to what I call "retrieval chipping": "Retrieval chipping" often has the pattern of two slightly different chips occurring at once close together, this delineating the outer areas of the "pinched" portion: The accidental retrieval "twisting" creates more shear force away from its center axis, hence the "double chipping" away from the center of twisting...

This typically does not happen with Sabre Hollow Grinds blades because, even with thinner edges, the faster increase of cross-section thickness (after it begins, and it of course begins later on hollow grinds than on flat grinds) either pushes the wood apart more forcefully, or naturally "unsticks" the edge better, preventing lateral loads: A hollow grind in effect "naturally" converts lateral loads into vertical "unsticking" motion... A flat grind does not convert lateral forces into vertical motion so well, or it does it less forcefully, so the edge bending just continues without any "unsticking", which sometimes leads to more lateral loads being involuntarily applied...

It is hard to avoid accidental "twisting" in the woods, because the level of "stability" of the wood chopped in the field can vary from thin branches moving around, to very rigid and thicker logs that have softened on the outside. In other words, the retrieval motion is not consistent, and does not have the same effects...

Now Sabre Hollow Grinds are lesser performance "choppers", in absolute terms, compared to Full Flat Grinds, but they get closer if their better protection of sharper edges (by lowering the primary grind line) is factored in: In other words, Full Flat Grinds have to be less sharp for the same durability... Sharper thinner edges mean more versatily in the tasks a chopper can accomplish, so Sabre Hollow Grinds are more versatile, all else being equal...

Another big difference is 10" Sabre Hollow Grind choppers are typically over 20-24 ounces, while Full Flat Grinds are much lighter at around 17-19. This is outweighed in my opinion by the better protection of the edge against lateral loads offered by Sabre Hollow Grinds, especially for emergency shelter building, which is very taxing on a knife...

Gaston

 

[FortyTwoBlades]

Hollow grinds are typically much more susceptible to side loads than flat or convex grinds because the hollows are brought quite thin comparatively speaking. But any grind type can be made thinner or thicker as the design dictates. Grind names are really just describing the visual effect of a certain geometrical/angular geometry imposed on the given stock.

 

[DeadboxHero]

So awhile ago I was In a big knife store fondling many knives and one thing I found was regardless of price point many suffered from poor edge geometry. I would say 90 percent that had poor edge geometry were often times simply too thick to cut well. To my surprise this included many 200-350 dollar knives. Im speaking of production knives here of course. Im not going to start a war and name the specific companies as I know most have many fans on here. I will say though out of all the fixed blades I handled the cheaper bucks and the like had very good edge geometry,compared to others with higher price tags and better steel. Its funny to think that some of those companies using such "superior" steels had big thick grinds. Now I get that many people abuse knives (Iv been guilty on more then one occasion).At some point does it not just become silly to make a knife with such a great steel with poor edge geometry?

Haha it's impossible to make a knife for everyone and everything, so when in doubt make it thick, the people that can use a more acute edge can usually sharpen and reprofile to their desired edge geometry and finish anyway so you can satisfy more customers with a thicker, toothy edge.

Honestly the average dude would benefit more from the thicker, toothy factory edges.

We forget that not every knife user posts here so we often live in a bubble of very obsessed knife afinanados and forget that not all of our preferences work for everyone.

Haha but yeah, I like the thinner edges on pocket knives

 

[Gaston444]

What is a sabre hollow grind?

It's a hollow grind with a flat portion below the spine.

And no, it is not accurate to say they are more susceptible to side loads, because the portion that would make this true, the portion that is thinner than a flat grind, is not where most of the side loads would concentrate: The side loads would inevitably focus higher.

This remains true even if, when chopping at the side of a V cut, the blade is in full contact on one side, with only the edge engaged into the wood on the "open" side: You would think that having just the edge engaged on one side would make it vulnerable to twisting, but it doesn't happen...

This is because upon twisting, the fully engaged side still pulls the edge upwards owing to the hollow shape, and this upward pull diffuses the forces away from twisting the edge.

It is not immune to damage, of course, but the Full Flat Grind is absolutely far more vulnerable...: You can make out the chipping "pairs", happening audibly, and at once, on pull-out, facing each other on these two similar flat ground knives, one in tough 5160, the other in D-2: About as opposite steels in toughness as you can find, yet they behaved pretty much the same, chipping on the pull-out...; The 5160 knife (below) was 0.020", the D-2 was 0.030", so that accounts for some of the differences: The 5160 had to have its angle opened to over 15:

Gaston

 

[noob93]

It's a difficult thing for manufacturers to get right it seems. I've seen all sorts of bizarre geometry on a factory edge.

Had a Blur that was at about 8 degrees with an extremely tall bevel on one side and probably 35 degrees on the other. Almost a chisel grind.

Just recently I had a knife the was so obtuse the Wicked Edge guides actually didn't allow enough travel to match it. Spent an hour back-bevelling just to get it to 25dps, which still would've been a bit too thick by my standards.


Perhaps they just err on the side of caution and allow the customer to make modifications to the edge. Except for Microtech of course.

thats strange Iv never had that on a knife though I have had uneven grinds and what not. People always jump on me when i say this but I will say it again lol. I bought an essee izula after it got so much hype. I figured the edge geometry would be quite a lot thinner as it was toted as a replacement for a folder for edc tasks. That being said I found it overly thick with a slighly uneven grind. Thus not only making it not cut well but making it harder to sharpen as well. It really sucked because I think its a great design that deserved better. I just simply do not have the equipment or skill to reprofile the edge and it usually just gets used as a backup. That knife in particular made me want to investigate other companies edge geometry and Iv been unimpressed since. I get companies needing to tread lightly because of warranty claims but how many guys have the skill/equipment or time to correct those errors? I guess its not so bad when were talking about a simple high carbon with the right set up and skills. What happens when you have that problem with say d2 or s30v? sure most people are lucky enough to live somewhere with a knife shop or what have you at the least but some of us including myself do not. btw are you praising microtech for there edge geometry? I ask because iv never tried one or even had one in hand.

 

[CornSyrup]

A very well set edge can make a knife which is thick behind that edge cut decently. At the same time, a poor edge paired with a knife which is thin behind that edge can also cut decently.

Unevenness of either the bevel grinds or the edge grind, in my view, has the smallest impact on cutting performance compared to how thin the knife is behind the edge and how finely (absent of burrs, dents or chips) that edge is ground.

 

[FortyTwoBlades]

Yet again, I don't have the time or energy to expend on a prolonged debate, but I'll simply caution folks to take Gaston's comments here with a rock crystal of salt. That's not how this stuff works, and a blade made thin immediately behind the edge with an abrupt transition is going to be far more prone to damage from side-loading than one that is of continuous taper and thicker total geometry behind the edge. Examples of hollow ground chopping blades having their edges blow out abound with even cursory research, and there's a reason why most choppers do not make use of hollow bevels.

 

[noob93]

I'll just chime in to say I feel your pain Noob93.

I have a decent sized collection of both high-ish end Spydercos and Bussekin, but just accept that the edge geometry is going to be sort of a crapshoot in terms of being in line with my personal preferences because I favor the designs. Though I believe Spyderco has been trending towards thinner grinds lately, I've received a few head scratchers from them. I do understand the pratical issue that manufacturers have to protect themselves against warranty problems as well.

I've been slowly building up my competence with reprofiling and regrinding, which has been a big help. I've practiced a lot on my 1x30" with very cheap knives, MTech, etc... and it's funny how I'll sometimes grab those $10-$15 regrinds over much "nicer," more expensive blades simply because they cut so much better and, like Josh said, I don't have any concerns about damaging them.

As an aside, I also thought experimenting with very cheap knives would be an interesting baseline to have a comparison against higher end production steels and heat treats. In general though, I haven't been able to tell much difference between how "good" or "bad" steels perform in use at all. The conclusions I've drawn are that, for me, geometry/cutting ability and ease of sharpening trump most other factors in the user blades I favor the most for moderate to heavy use. For light use edc blades, I just carry whatever I want to on any given day because geometry, etc aren't overly critical to accomplishing menial tasks.

I always wanted a busse but generally prefer a fixed blade to be around 6 inches or less and always figured with the warranty would come a thick edge. spyderco definitely has some blades with good geometry and some that are a bit thick but nothing compared to some other companies. Its a shame I dont like the aesthetics and or ergos of most of them or id certainly own more. I wish I had a belt grinder myself sometimes but im pretty obsessed with learning free hand only. Thats quite interesting you should do a video demonstrating that.. Now I know there would be plenty pi**ed off fanboys but it would prove a point. I agree on the edc but there have been times where I worked in certain places where I required something with certain traits. warehouse job needed edge retention with decent toughness for boxes,crates and plastic junk whereas my lumber yard job required toughness and flexibily.

 

[pinnah]

Gaston, point You Tube at "Buck Reaper Fail" and you will find two dramatic examples of the sort or side load damage that 42Bkades was describing.

 

[MarkN86]

Gaston, point You Tube at "Buck Reaper Fail" and you will find two dramatic examples of the sort or side load damage that 42Bkades was describing.

Ouch, I did not realize just how thin the Reaper was. And just after I got done talking them up.

 

[BluntCut MetalWorks]

Not much data you can draw/extract from these little chips/fractures. In testing, I often induce large chip/fracture (5-10mm diameter). Rather than me telling you what I saw, perhaps best you see it yourself.
Repro steps: put a 4-5mm wide large micro-chisel on your bevel. Chop into 6mm dia brass rod or nail or cross grain into katalox/cumaru/etc. Make sure edge is stuck. You should able to spot/observe edge has steered very badly. The bend edge is half cracked (stretched side), on extraction/pull-out, often lead to complete fractured (piece of the edge stay in material).

It's a hollow grind with a flat portion below the spine.

And no, it is not accurate to say they are more susceptible to side loads, because the portion that would make this true, the portion that is thinner than a flat grind, is not where most of the side loads would concentrate: The side loads would inevitably focus higher.

This remains true even if, when chopping at the side of a V cut, the blade is in full contact on one side, with only the edge engaged into the wood on the "open" side: You would think that having just the edge engaged on one side would make it vulnerable to twisting, but it doesn't happen...

This is because upon twisting, the fully engaged side still pulls the edge upwards owing to the hollow shape, and this upward pull diffuses the forces away from twisting the edge.

It is not immune to damage, of course, but the Full Flat Grind is absolutely far more vulnerable...: You can make out the chipping "pairs", happening audibly, and at once, on pull-out, facing each other on these two similar flat ground knives, one in tough 5160, the other in D-2: About as opposite steels in toughness as you can find, yet they behaved pretty much the same, chipping on the pull-out...; The 5160 knife (below) was 0.020", the D-2 was 0.030", so that accounts for some of the differences: The 5160 had to have its angle opened to over 15:

Gaston

 

[pinnah]

Ouch, I did not realize just how thin the Reaper was. And just after I got done talking them up.

I have one and with some mods, it became a decent knife for the price. It would be a much better knife IMO with a sabre flat or even a full flat grind

 

[inkynate]

I wish I had a belt grinder myself sometimes but im pretty obsessed with learning free hand only. Thats quite interesting you should do a video demonstrating that.

I can respect that. I also waited until I was decent at freehand sharpening before I got the 1x30". Even did a couple of full regrinds by hand with very coarse stones. That said, power makes material removal waaaaay faster and more enjoyable The harbor freight belt sander is very cheap, but I've had a lot of success with it for what it is.

I don't have any videos, but there are plenty of them already out there on youtube if you ever decide to pick one up. I watched a lot of Gavko's vids when I first got started. The main differences are that I put mine up on a workbench (he was short on space at the time,) and I rigged up a drip line for wet grinding.

[video=youtube;9ATukKnCbbE]http://www.youtube.com/watch?v=9ATukKnCbbE[/video]

Here are a couple of my ugly ducklings, (as a beginner, I liked regrinding hollow ground blades to thinner flat or high-saber grinds the most because it's fairly easy):

 

[MarkN86]

I have one and with some mods, it became a decent knife for the price. It would be a much better knife IMO with a sabre flat or even a full flat grind

The knife would probably work for me, but then again I don't even put my Kabar through more than 2" diameter if I need to baton.

 

[Gaston444]

Not much data you can draw/extract from these little chips/fractures. In testing, I often induce large chip/fracture (5-10mm diameter). Rather than me telling you what I saw, perhaps best you see it yourself.
Repro steps: put a 4-5mm wide large micro-chisel on your bevel. Chop into 6mm dia brass rod or nail or cross grain into katalox/cumaru/etc. Make sure edge is stuck. You should able to spot/observe edge has steered very badly. The bend edge is half cracked (stretched side), on extraction/pull-out, often lead to complete fractured (piece of the edge stay in material).

I understand what you mean, but in the case of my small chips, I did accidentally twist the blade on extraction, and I heard or felt, the break upon the twisting, and not during the actual extraction (although they were closely spaced, so you have to take my word for it)... And the chipping did occur in pairs, with the twisting centered between the pairs...

Furthermore, if you looked closely at the chips, you would see some bending in opposite directions, which matches the notion of all the damage occurring on twisting, while it would take an amazing coincidence for this to happen TWICE due to random bending on insertion, especially in opposite directions matching my twist direction...

In fact, the twist direction of the break "lips" at the break line is what confirmed (to me) the reason for the damage...

More interesting still, the same kind of twisting damage did not happen on deep hollow grinds on thick 1/4" stock, for the obvious reason that a hollow grind on such thick stock "flares" so rapidly that it compresses the wood far more, and this closer to the edge: More compressed wood obviously works harder to prevent lateral movements, or converts it to unsticking: This is self-evident if you compare the amount of "wiggle" a hollow grind on thick stock will allow once buried up to very near the primary grind line, compare to the wiggle you will get from a similar depth on a Full Flat Grind...

The simple fact that a thin Full Flat Grind with a very broad blade will make sharp "singing" sounds also suggests it is less rigidly pinched by the wood...

Gaston

P.S. As to how low-cost, light and thin-bladed, Buck knives behaved, I think you would have to show a range of much heavier 1/4" stock hollow grind knives doing the same to make this convincing...: Such a small light knife will have trouble burying the blade beyond the portion where the hollow grind is more vulnerable, which kind of invalidates the comparison... Also Bucks are well-known to be on the brittle side, so they hardly make a universal reference...

 

[jdm61]

And yet the original cleaver style CPM M-4 "race knives" were full height flat grind with an above the edge thickness of like 0.015........ Your mileage may vary.

It is not that simple...

For chopping wood in the field, what I've found is, if the steel is good quality, a sabre hollow grind blade will tolerate much thinner angles while chopping, while a Full Flat Grind blade will require a thicker more open angle edge.

With a Sabre Hollow Grind, the edge angle can be as low as 12 degrees per side on a 0.020" edge base, and it will tolerate chopping all day long. (Such as a Randall Model 12)

For a Full Flat Grind knife, the edge angle will have to go up to at least 15 degrees per side, preferably sitting on a 0.030" base. Even that is borderline...

(This would not apply to a fully convexed chopper like the SM III Trailmaster or the Fallkniven Thor, because they are not true "Full Flat Grinds". I have found the SM III Trailmaster to be so thickened by the overall convexing that it performed extremely poorly: On these knives, achieving a 15 degree per side final angle is impossible or unlikely anyway, because of their overall "swelled" thickness.)

There are multiple reasons for this particular superiority of Sabre Hollow Grinds, one of the less obvious factors being that wood left on the ground, in the wild, will often "soften" on the outside and "harden" on the inside, creating a medium that will allow more aggressive lateral loads which are more concentrated on the edge itself.

This is because the softer outer will offer less support and allow more accidental twisting movements when unsticking the edge, while the harder inner core will trap the edge more forcefully in a more concentrated manner, often leading to what I call "retrieval chipping": "Retrieval chipping" often has the pattern of two slightly different chips occurring at once close together, this delineating the outer areas of the "pinched" portion: The accidental retrieval "twisting" creates more shear force away from its center axis, hence the "double chipping" away from the center of twisting...

This typically does not happen with Sabre Hollow Grinds blades because, even with thinner edges, the faster increase of cross-section thickness (after it begins, and it of course begins later on hollow grinds than on flat grinds) either pushes the wood apart more forcefully, or naturally "unsticks" the edge better, preventing lateral loads: A hollow grind in effect "naturally" converts lateral loads into vertical "unsticking" motion... A flat grind does not convert lateral forces into vertical motion so well, or it does it less forcefully, so the edge bending just continues without any "unsticking", which sometimes leads to more lateral loads being involuntarily applied...

It is hard to avoid accidental "twisting" in the woods, because the level of "stability" of the wood chopped in the field can vary from thin branches moving around, to very rigid and thicker logs that have softened on the outside. In other words, the retrieval motion is not consistent, and does not have the same effects...

Now Sabre Hollow Grinds are lesser performance "choppers", in absolute terms, compared to Full Flat Grinds, but they get closer if their better protection of sharper edges (by lowering the primary grind line) is factored in: In other words, Full Flat Grinds have to be less sharp for the same durability... Sharper thinner edges mean more versatily in the tasks a chopper can accomplish, so Sabre Hollow Grinds are more versatile, all else being equal...

Another big difference is 10" Sabre Hollow Grind choppers are typically over 20-24 ounces, while Full Flat Grinds are much lighter at around 17-19. This is outweighed in my opinion by the better protection of the edge against lateral loads offered by Sabre Hollow Grinds, especially for emergency shelter building, which is very taxing on a knife...

Gaston

 

[The cow]

It is pretty much par for the course that knives have thick grinds. Unsurprising considering what knives were being used for in the last 5+ years. Every yahoo with a youtube channel was taking their knife and bashing it through the thickest, knottiest piece of wood they can find, baton through a nail, and pry stuff out with it. Those that failed were deemed terrible knives. Makers naturally responded with stupid-proof blades.
Most people don't care enough or use their knives enough to find the perfect edge.
Belt knives, I opt for a thinner edge. Choppers, I opt for a thicker edge but still often thin out factory edges.

 

[Gaston444]

Gaston, point You Tube at "Buck Reaper Fail" and you will find two dramatic examples of the sort or side load damage that 42Bkades was describing.

I realize now that all those Buck Reaper failures are due to batoning...

Yet my argument was all about hollow grinds and chopping performance: I don't know what chopping performance has to do with batoning, or why anyone would bring something completely irrelevant as an example of failure...

My increasingly relevant opinion of batoning is that it is not a legitimate way to use your knife, which is exactly why you never heard of it in the distant past, and why it is still not recognized as a word by the computer's glossary, even on this site... I does give a great excuse for makers to produce a great number of terminally dull pry bars though....

Gaston

 

[lamanian]

You want a knife from a high end company with terrific edge geometry? Get a Ritter Griptilian. Or if you really want the best a CRK Sebenza 21