Edge Testing - Blades That Cut Metal

A

anonymous76

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Feb 10, 2019
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I have read of blades that could be hammered through coins, nails or even steel. Generally I would think such testing is excessive, but it would be interesting (to me anyway) to see the absolute limit of a test blade. A test as described above is really qualitative. There are uncontrolled variables (e.g. changing striking force, angle of force delivered to blade, deflection of the edge) to account for. I have been toying with the idea of making an apparatus for cutting metal with a test blade. The idea is to cut down on the variables and produce data that is more quantitative. Think of it like a guillotine with a set weight that strikes a piece of metal (aluminum, brass, steel, whatever) held over a secured test blade edge up. I should point out that I am NOT a physics guy. To keep it simple I think I would start with a 1 meter drop and a 1 kg weight. The effects of friction could be minimized by making the apparatus out of polished UHMW or Teflon. By my thinking the first strike would give information about edge geometry. The thinner the edge and the slighter the angle, the deeper the blade would cut into the metal. Subsequent strikes, if the blade were to survive, would tell how well a blade handles the build up of stress at the edge. Determining how many blows the edge takes before the edge deforms (brittle or ductile) would be the ultimate test. It may take many cuts depending on the type of metal used and the steel and HT of course. Does this sound interesting or even useful?
 
It would be a tremendous work to do and will cost .Too many different steel to try , then all of them will act different on different hardness ..Then different edge geometry.............I do some test like that and found that geometry which will cut nail without damage is not useful on knife .
 
Thanks for the feedback Natlek. To be honest I was just using the nails or steel as an example. I was actually thinking of using a softer metal like brass or aluminum. It would take some trial and error to figure out what works best. I am particularly interested in testing tougher alloys such as L6 and 5160.
 
Would be interesting. But you'd have to use blades with the same geometry, and heat treated to greatest potential.
 
Jux t, perhaps not heat treated to the greatest potential, but used to determine the the HT of greatest potential. Greatest potential edge toughness that is. For instance one of the first set of tests I want to do would involve hardening test blades in various quenching mediums, starting with fast oil and progressing to slow. Each test blade would initially be tempered at a low temperature, say 350F. It would then be tested for edge toughness near the tip in the apparatus described above. Brittle failure would be expected at such a low temperature. The blade would be made long enough that multiple tests could be conducted. Next the blade would be re-tempered slightly hotter (e.g. 375F) and be re-tested an inch or so from the first test... and so on and so forth until ductile deformation of the edge occurs. What I really would like to get at is that transition from brittle to ductile deformation of the edge with such an extreme test. With so many HT variables to test I don't expect to make finished knives for a very long time.
 
you are asking for opinions so I'll give you mine :D
It seems like you are trying to make a contribution to the knife industry, but I'm not certain on what "problem" you are trying to solve...it seems like this testing is beyond the point of diminishing returns, at least from my POV.

I work with laminated steels alot, it's difficult to test the hardness on a scale. The core is very hard at 63-64 RC and the cladding is soft. The way I do it (and was taught) is when the blade is ground and exposed to about the thickness of a dime, you can cut steel with the edge, and I do this with every blade to "check" the hardness. I can at that point also chop a nail with no edge damage. When the core gets thinner, neither of these checks work as the core is too thin, brittle, unsupported etc.

Aaron Gough did a steel destruction test when he first started and documented it. I'm certain he did it for himself to determine the best steel for the knife he wanted to build. I don't know that many other knifemakers even use his test results as a guide in determining what steel they want to use for their knife build. Of course I'm sure some do.

So my response is I think it would be interesting (to some) but mostly useful to just you.
So you should do it for yourself. For example, I can't see what value this testing and results would be to a kitchen knife or folder maker, but it could useful to someone who wants to make an outdoor knife.

regards
Harbeer
 
Sounds like you are testing a knife like a chisel.

Honestly knives cut, people really to stop beating on them like a red headed step child.
 
Too bad Noss's destruction testing is gone.

Hundreds of hours of chopping concrete, steel pipe, angle iron, putting the knife in a vice and hitting it with a sledge hammer!!!

Many expensive knives failed fast. Some expensive knives were unbreakable (Busse, Scrapyard, Swamprat, custom by Dan Keffler...if I remember)
 
Bigfattyt said:
Too bad Noss's destruction testing is gone.

Hundreds of hours of chopping concrete, steel pipe, angle iron, putting the knife in a vice and hitting it with a sledge hammer!!!

Many expensive knives failed fast. Some expensive knives were unbreakable (Busse, Scrapyard, Swamprat, custom by Dan Keffler...if I remember)
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One has to rule out geometry first. Everyone comes to the conclusion that it's unbreakable because of fancy steel when in reality it's hiding behind thick geometry.
 
DeadboxHero said:
One has to rule out geometry first. Everyone comes to the conclusion that it's unbreakable because of fancy steel when in reality it's hiding behind thick geometry.
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I've owned more than. My share of them. Most cut very well. Some of the big choppers had thick spines, but still bit DEEP!!

I've had EDC folders thicker behind the edge than some of my Busse.

They have had plenty of models too thick bte!!

But the steel they use is no joke, thick or thin.

My CPM3V customs have better edge retention and are just as tough, but much harder to sharpen!! Also not as stain resistant.

I've used a lot of steel from production makers to custom makers. Most of the 10xx steels, 5160, INFI (new version, higher hardness version, old original recipe), 52100, SR101 (Busse's version of 52100), a2 CPM3V, L6, AEBL, VG10, VG1, CPM154, 440c, 420HC, Aus8a, Krupp 4116, Sandvik 12C27, and more I'm forgetting...


I've broken knives, thrown them, batoned, used them as a chisel, hammer, spear, I've made them, heat treated them, reground production knives.

I've reground Busse too.

I've sold off all but one Busse in favor of custom knives.... but still like them. If I were told I could only bring one big knife on a long, no rescue trip, I'd probably still take a Busse.
 
I am not suggesting that knives should be meant to cut metal. I started off by stating that I thought such testing would probably be excessive. I wanted to get some opinions about whether or not others thought it was. After years of heavy use, stresses can build up in blade steels leading them to unexpectedly break. I believe this process would be sped up by abuse. One of my earliest memories of a knife failing me involved a store bought pocket knife. After several years of use the tip unexpectedly broke on me. This puzzled me at the time since it always seemed flexible. I could literally flex the tip by hand. I have since seen this happen more than once. You may say that this was due to HT that was less than ideal, but I have seen this happen to knives from major brands (I won't name names). Besides an ideal HT is what I am trying to get at. So Harbeer, the question I am attempting to answer is how much stress build up can a blade take before failure (break or bend). By testing an edge against metal through cycles (strikes) of stress, I believe that you would greatly speed up the process and determine how much stress a blade could take. I am a bit paranoid when it comes to this, because the last thing I would want is for a customer to come back to me with a broken blade. I don't think it would reflect well on my abilities and is potentially dangerous to the customer. As for this only being of use to me, I fully intend on sharing what I do. If I were to move forward on this I would post my findings, listing all HT parameters. Whether or not this would be of interest to the reader, obviously depends on the individual.
 
"Stress" doesn't build up appreciably in normal use, however damage does. The damage makes a point where a stress riser can form.

You broke your pocket knife by bending it beyond the elastic limit, or because there was a damaged spot where you were flexing it..

Once a knife is properly HTed, the stresses should be taken care of … assuming a proper HT.
 
Surprisingly, I test my knives similar, so does Scott gossman. It’s not because I think I’ll have to cut through a truck, although you never know. It’s to gauge my heat treat, and just general toughness of the steel. It’s so I can decide on my geometry that will hold up to a hunter hacking through an elk rib cage, or splitting a deer pelvic bone. If it can handle steel, it’ll handle bone! If I can take my hunting blades down to .020 behind the edge, 20 dps, or a zero convex, And it can handle mild chops on steel, then I don’t have to worry about bone! Yet it will still skin out and quarter an entire elk without resharpening! It’s one way to test. The other is cut tests of various kinds, such as skinning a rutting bull elk covered in mud! Or Manila rope. I start with cut tests, move to antler, then to cinder block and metal.
Why? Because it helps me dial things in. Last year, on my elk hunt, it was getting really hot really quick, and me and my dad were in a hurry to work my bull, before the meat started getting bad. To cut the head, he couldnt hold it up so I could find the vertebrae and cut it with my knife, so he pulled out a cheap Chinese junk mini axe he got from the Rocky Mountain elk foundation. I used a piece of oak to baton through the neck and tore the hell out of the edge on that axe. It broke so I ended up throwing the piece of junk away. So now I’m making my dad a similar pattern out of s7 steel, with a chisel ground end on the pack for splitting bone, you know just in case!
 
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Because of these tests, I’m settling on ztuff for my personal knives! It has good enough wear resistance, but can handle any field chores I’ll encounter! Now for caping, and skinning the head, I’ll make a nice thin knife for me in vanadis 4e. 4v and 3v and zwear are other steels that handle these chores pretty well. All very tough with good enough wear resistance for skinning blades. Yet these can be touched up easily in the field. I’ve yet to need a 10v blade or something similar with extreme wear resistance. Most hunters couldn’t touch these steels up anyway!
 
People cut things with knives, including metal. It's not that weird. I'll deburr a thread or dig a steel chip out of an aluminum fixture or cut a copper wire with my folder frequently. We open crates with a knife and a hammer, it's faster and easier to cut through the nails than to pry them, and a hacksaw is no good. An upshot to this is no boards with nails sticking out laying around. Cutting through metal banding straps with a knife and a hammer is not weird and the knife we use to do that is surprisingly thin.

Cutting metal is not weird. You can do more damage to a knife with a wonky cut on wood than carful cutting of unhardened steel or aluminum.


Wear resistance and edge retention are very different things. Sometimes opposite things. For example a very high alloy steel with a lot of carbide may have very high wear resistance and test very well on "edge retention" in rope or card stock but have poor edge retention in regular use due to the lateral loads put on a blade when carving into something or clacking something hard like a staple or a beer bottle etc. This is where edge stability is important and you will find that the simple steels often have the best edge stability.

Some steels, 4V and V4E, with a cutlery optimized HT have a pretty hard sweet spot and a moderate carbide volume and have that combination of wear resistance and edge stability that give good edge retention. 3V can be pretty good too. These are steels can be run at reasonable edge geometry and still cut slivers off a steel nail without too much problem. Steels like 52100, W2, and even lowly 1095 have always been able to do this with the right heat treat but the modern "super steels" and stainless steel have been so mushy/crumbly for slow long and cheap simple steels knives have had such crappy heat treat that people have started to view crummy edge stability as normal. It shouldn't be.

Most normal people (not knife nuts) are very pleased with an 18 DPS edge angle. That's much narrower than most factory knives and your mom's kitchen knife. And a decent steel with a good HT run at that angle can cut metal. We do it all the time.
 
Nathan the Machinist said:
People cut things with knives, including metal. It's not that weird. I'll deburr a thread or dig a steel chip out of an aluminum fixture or cut a copper wire with my folder frequently. We open crates with a knife and a hammer, it's faster and easier to cut through the nails than to pry them, and a hacksaw is no good. An upshot to this is no boards with nails sticking out laying around. Cutting through metal banding straps with a knife and a hammer is not weird and the knife we use to do that is surprisingly thin.

Cutting metal is not weird. You can do more damage to a knife with a wonky cut on wood than carful cutting of unhardened steel or aluminum.


Wear resistance and edge retention are very different things. Sometimes opposite things. For example a very high alloy steel with a lot of carbide may have very high wear resistance and test very well on "edge retention" in rope or card stock but have poor edge retention in regular use due to the lateral loads put on a blade when carving into something or clacking something hard like a staple or a beer bottle etc. This is where edge stability is important and you will find that the simple steels often have the best edge stability.

Some steels, 4V and V4E, with a cutlery optimized HT have a pretty hard sweet spot and a moderate carbide volume and have that combination of wear resistance and edge stability that give good edge retention. 3V can be pretty good too. These are steels can be run at reasonable edge geometry and still cut slivers off a steel nail without too much problem. Steels like 52100, W2, and even lowly 1095 have always been able to do this with the right heat treat but the modern "super steels" and stainless steel have been so mushy/crumbly for slow long and cheap simple steels knives have had such crappy heat treat that people have started to view crummy edge stability as normal. It shouldn't be.

Most normal people (not knife nuts) are very pleased with an 18 DPS edge angle. That's much narrower than most factory knives and your mom's kitchen knife. And a decent steel with a good HT run at that angle can cut metal. We do it all the time.
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I have been super happy with M4 on my folders over the years but lately it seems like 4V is becoming more popular for similar knives. Are there things that 4V will do that M4 will not? Or is there a little bit of newer is better going on?

Sorry I didn't mean to derail. I thought this was semi related to the subject and also you have probably tested both.
 
Bigfattyt said:
Too bad Noss's destruction testing is gone.

Hundreds of hours of chopping concrete, steel pipe, angle iron, putting the knife in a vice and hitting it with a sledge hammer!!!

Many expensive knives failed fast. Some expensive knives were unbreakable (Busse, Scrapyard, Swamprat, custom by Dan Keffler...if I remember)
Click to expand...

Almost unbreakable. Noss was only unable to break the Keffeler monster, but at that thickness it would take much more than man power to do so. It was Noss fault that I love thick knives made in ultra tough steels.
 
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