Knife Toughness "Measurements"

[jffielde]

Hello, all. First time post, so I'll try to make it a zinger.

I'm a knife noob, but I'm starting to appreciate the craftsmanship, elegance and utility of different knives. I've learned a lot lurking here, and have been entertained by some of the toughness discussion and links to destruction and other toughness testing. Most of the testing is so limited (often just one!), varied, and non-repeatable that it means little, but it's fun to watch and maybe there's a little value there somewhere.

So here's my contention: it's not very useful to evaluate knife toughness without taking size and weight into account. Making a tough knife with limitless size and weight constraints isn't much of an achievement. It seems like taking any pretty strong knife and scaling it bigger results in a stronger knife, but it increasingly fails as a knife (directly as a slicer and indirectly for convenience of carrying it) the bigger/heavier it gets. Accordingly, I'm not impressed with toughness when it appears in knives of greatest size and weight. In those cases, I merely expect it.

It's also dangerous to the manufacturer to rest its reputation on toughness, since it's easy to mimic/exceed for much lower cost (eg, Zero Tolerance taking business from knives 3-4x the cost), if size and weight don't matter much.

Accordingly, I'd appreciate some recommendations for knives that are tough beyond what's expected of their size and weight - knives that fight above their weight-class. Cost matters little. Thank you for letting me introduce myself through a request.

Joseph

 

[Insipid Moniker]

What you're getting at is the inverse relationship between efficiency and resiliency. If you want knives that are very tough while still maintaining good cutting efficiency look into steels like S7, 5160 and CPM-3V for fixed blades. As for folders, I would recommend some of the new Cold Steel offerings. The Finn Wolf, in particular, should punch well above its weight given the Scandi grind, which leaves a lot of steel behind the edge, and the Triad lock and generally overbuilt/reinforced hardware that Cold Steel often puts into their folders.

 

[marcinek]

Welcome. Your post might be more clear if you hadn't used "toughness," which is a measurable quality of steel which has nothing to do with what you are taking about.

 

[yepimonfire]

Accordingly, I'd appreciate some recommendations for knives that are tough beyond what's expected of their size and weight - knives that fight above their weight-class. Cost matters little. Thank you for letting me introduce myself through a request.

Joseph

Anything by cold steel.

The videos are goofy but legitimate and repeatable.

[video=youtube;1zd3Jg5Fdms]https://www.youtube.com/watch?v=1zd3Jg5Fdms&list=PLF4EA0FC3A3702C31&index=9[/video]

 

[jffielde]

i like the video. Thanks.

 

[Sonnydaze]

For steels that are generally available, I would go with CPM-3V. Note that "toughness" is often inversely proportional to "wear resistance" which is the tradeoff that you will face. SurviveKnives is a brand that is rather famous for their GSO series of fixed blades, available in 3V, 20CP, S90V. They have a rather wide series of blade-lengths available.
If you're a folder guy, try the Spyderco TUFF...which is a great folding blade that was designed to be a "folding" fixed-blade.

 

[jffielde]

Welcome. Your post might be more clear if you hadn't used "toughness," which is a measurable quality of steel which has nothing to do with what you are taking about.

You are right. I'm interested in the knife failing, not how tough the steel is. I'm not asking specifically about steel, but the knife as a whole and its likelihood of failing. Thanks for clarifying.

 

[MatthewSB]

For a folder, I'm very impressed by my Sebenza 25. There's a Carbon Fiber slabbed version that weighs in at 4 oz, with a beefy (enough) blade, massive pivot, and rock solid lock system I believe it to be about as strong a folder as one can find.

 

[marcinek]

You are right. I'm interested in the knife failing, not how tough the steel is. I'm not asking specifically about steel, but the knife as a whole and its likelihood of failing. Thanks for clarifying.

I actually agree with your contention. Its "hard use/thick" vs "slicing/thin" as far as blades go. You just cant have a thick slicer. Physics.

As far as the rest of a folder, barring a bum blade, it really comes down to the strength of the pivot. Scales and frames aren't going to break.

And of course the "toughest" pivot?

No pivot.

 

[Shorttime]

So if I understand the question, what you're looking for is some kind of index between the cutting force required for a given knife (something like CATRA tests), and the same knife's ability to withstand shock, strain, and lateral torque without failing?

If so, then you've got a contender for a college final exam paper!

To the best of my knowledge, there has never been a study that compared those two things, but it sure would be interesting.

There has been a lot of informal testing done. Anybody who has ever tried to power through one more job with a dull knife sooner or later develops an opinion on how blade shape and bevel angles effect cutting performance, and how easily a given lock will unlock if you grip the wrong thing the wrong way.

I would look at the relative merits of the various lock methods first, then compare blades.

Cold Steel's Triad lock, and the AXIS Lock that Benchmade uses, have some numbers to back up the claim that they are better able to resist closing force than liners, framelocks, or conventional lockbacks. Some people have had issues with the springs Benchmade uses to hold the AXIS pin in place, and the Triad Lock takes more pressure to disengage than a similar-size lockback, so your mileage may vary.

I hope that helps. And, if you decide to assemble an article comparing lock strength and cutting performance, please post here, first!

 

[yepimonfire]

So if I understand the question, what you're looking for is some kind of index between the cutting force required for a given knife (something like CATRA tests), and the same knife's ability to withstand shock, strain, and lateral torque without failing?

If so, then you've got a contender for a college final exam paper!

To the best of my knowledge, there has never been a study that compared those two things, but it sure would be interesting.

There has been a lot of informal testing done. Anybody who has ever tried to power through one more job with a dull knife sooner or later develops an opinion on how blade shape and bevel angles effect cutting performance, and how easily a given lock will unlock if you grip the wrong thing the wrong way.

I would look at the relative merits of the various lock methods first, then compare blades.

Cold Steel's Triad lock, and the AXIS Lock that Benchmade uses, have some numbers to back up the claim that they are better able to resist closing force than liners, framelocks, or conventional lockbacks. Some people have had issues with the springs Benchmade uses to hold the AXIS pin in place, and the Triad Lock takes more pressure to disengage than a similar-size lockback, so your mileage may vary.

I hope that helps. And, if you decide to assemble an article comparing lock strength and cutting performance, please post here, first!

A really good edge geometry test at home is slicing through cardboard. Poor geometry binds easily.

As far as tri-ad and axis locks go, triad beats it. It's highly unlikely a triad lock will fail during use, you're more likely to snap the blade at the pivot.

[video=youtube;fNYJdU6XypM]https://www.youtube.com/watch?v=fNYJdU6XypM[/video]

 

[marcinek]

A really good edge geometry test at home is slicing through cardboard. Poor geometry binds easily.

As far as tri-ad and axis locks go, triad beats it. It's highly unlikely a triad lock will fail during use, you're more likely to snap the blade at the pivot.

The bugbear is that the two are entirely unrelated. You could take a CS Tri-Ad and slap an Opinel blade on it. I don't know where that gets you.

 

[Shorttime]

The bugbear is that the two are entirely unrelated. You could take a CS Tri-Ad and slap an Opinel blade on it. I don't know where that gets you.

Yeah, that was my point, although I took a long time to get to it.

Nobody has ever evaluated a folder's "strength" on a "holistic" basis (including lock, blade, and handle slabs), so there isn't any data.

It's actually a fascinating discussion to me, because we stop talking about a straight relationship between blade thickness and knife strength, and move toward using engineering principles to make a knife that is as strong as possible for it's size.

But it's complicated, because now we're talking about materials choices for the handle slabs, pivot pin, washers or bearings, surface area contact between blade tang and lock, heat-treatment regimens for pivot pins and handle slabs, and predicting how any kind of load or force on the blade is going to be transmitted to the rest of the knife.

Although I would love to study all of this, I fear I am not smart enough.

 

[marcinek]

Although I would love to study all of this, I fear I am not smart enough.

Same here. Probably why I didn't get to your point. Short attention span. No doubt I saw something shiny.

 

[mbkingshane]

For steels that are generally available, I would go with CPM-3V. Note that "toughness" is often inversely proportional to "wear resistance" which is the tradeoff that you will face. SurviveKnives is a brand that is rather famous for their GSO series of fixed blades, available in 3V, 20CP, S90V. They have a rather wide series of blade-lengths available.
If you're a folder guy, try the Spyderco TUFF...which is a great folding blade that was designed to be a "folding" fixed-blade.

Agreed Spyderco tuff is just about as "strong" a folder as you're going to find. Maybe not the best slicer because of blade thickness, but it's a heavy duty sob.

 

[GrReaper]

it's not very useful to evaluate knife toughness without taking size and weight into account. Making a tough knife with limitless size and weight constraints isn't much of an achievement.

Accordingly, I'd appreciate some recommendations for knives that are tough beyond what's expected of their size and weight - knives that fight above their weight-class. Cost matters little. Thank you for letting me introduce myself through a request.

Joseph

Yes, I agree that assessing toughness of a particular steel or knife is limited to that particular model knife. It's hard to compare across different knives, since the design geometry, size and weight are different, let alone heat treat for different companies. Is a certain knife in CPM3V 3/16 inch thick tougher than another in 5/16 inch thick 1084 carbon steel? I don't know; I think you'd have to test them out side by side to find out. That said, what knife is tougher than their weight class? I'd think anything in CPM3V would be tougher than another knife of equal thickness in standard steels. 5160 and A2 are also very tough, although not as tough as CPM3V. As for fixed blade knives, I'd recommend the Bark River Bravo 2 in A2 as a very tough hard use knife, without being overly thick or heavy. I'm not sure if they have it CPM3V yet. At the time I got mine, it was only in A2. If they have it in CPM3V, by all means, that would be even tougher, assuming that they kept the same thickness and specs.

 

[lovemysteel]

So a thicker steel is tougher?

 

[lovemysteel]

I found these charts:

Seems like S7 is toughest steel. Do knife companies use this steel?

 

[Cobalt]

S7 is indeed one of the toughest steels available. It lacks good wear resistance and corrosion resistance. But for a hard use knife it is a good steel if properly heat treated.

Yes, you can get S7 knives. I have a pair of large custom choppers out of it.

 

[jffielde]

So if I understand the question, what you're looking for is some kind of index between the cutting force required for a given knife (something like CATRA tests), and the same knife's ability to withstand shock, strain, and lateral torque without failing?

If so, then you've got a contender for a college final exam paper!

To the best of my knowledge, there has never been a study that compared those two things, but it sure would be interesting.

There has been a lot of informal testing done. Anybody who has ever tried to power through one more job with a dull knife sooner or later develops an opinion on how blade shape and bevel angles effect cutting performance, and how easily a given lock will unlock if you grip the wrong thing the wrong way.

I would look at the relative merits of the various lock methods first, then compare blades.

Cold Steel's Triad lock, and the AXIS Lock that Benchmade uses, have some numbers to back up the claim that they are better able to resist closing force than liners, framelocks, or conventional lockbacks. Some people have had issues with the springs Benchmade uses to hold the AXIS pin in place, and the Triad Lock takes more pressure to disengage than a similar-size lockback, so your mileage may vary.

I hope that helps. And, if you decide to assemble an article comparing lock strength and cutting performance, please post here, first!

Thank you, Shorttime. That is a perfect statement of the question.