What do "Edge to Edge" impact tests prove? ( cool pics)

[Jerry Busse]

Along with the many mysteries of life there are many mysteries and/or urban legends and/or myths concerning bladeware. . . for example there are the infamous legends concerning “Surgical Stainless” and completely or partially enclosed “Full Tang” knives as well as integrated “Saw Blades” for wood that defy all common knowledge of wood saws. Couple this with the amount of nonsense that surrounds “Blood Grooves” and you’ve got yourself enough fodder for several nights of campfire stories that will be perpetuated for the next few generations. However, it is the homespun theories of edge testing that never cease to amaze and amuse. Some are clever and actually do demonstrate either the impressive or not so impressive characteristics of a knife’s performance. Others are more like magic tricks.

The one that I was overly impressed with when I was young was the “Edge to Edge” test. I was at a fellow knifemaker’s shop and stood in awe as he told me that his best selling technique was to simply chop into the edges of other manufacturer’s and maker’s knives. Wow! You really need to do this at a show to see the impact that it has on the consumer. They almost immediately reach for their wallet and start buying the winner of the contest. . . .which of course is the one with the thicker edge before bevel. What does this test prove? It proves three things: 1.) Primarily, it proves which knife has the thickest or most obtuse edge bevel. 2.) It shows how the edge is going to react to heavy impact by hard objects, like rocks. 3.) Mostly it supports the premise that con men and magicians count on. . . . smoke and mirrors and misinformation.

The only comparison that can be made between the two knives that impact each other is which one has the most obtuse or thickest edge bevel. THAT IS ALL!. . . . Sadly, and as far as I am aware, no other information can be gathered from these tests. As pointed out previously, you can learn about how one knife’s edge will respond to a heavy impact by a thin, hard object, and how the other one will respond to a heavy impact by a thick hard object. However, since you are not gathering the same information about the two knives from this test, it cannot qualify as a fair or equal comparison between the two knives. It’s fun to do . . . . . . It just doesn’t prove much.

In the following photos we used (Quite unfairly I might point out) a Battle Mistress at 58.4 Rc and a triple tempered D-2 shop knife that tests out at 62.3 Rc, and we did the Edge to Edge impact test. Now what was unfair? The fact that the D-2 blade was much harder in comparison to the INFI blade?. . .. After all it is a piece of steel that Rockwells at 62 Rc impacting a much softer 58 Rc blade. No, the unfair part was the obtuseness of the edge grinds, the advantage being given to the Battle Mistress.

In this first photo (below) you can see a standard view of the two knives after impact.

This photo (below) shows the two edges immediately after impact. The D-2 blade chipped out badly due in large part to the thinness of the edge bevel. The INFI blade actually has pieces of the D-2 blade lodged into its edge.

In this photo (below) the edge of the INFI blade has been wiped off to remove the D-2 edge chips and to reveal how the two edges held up to their respective impacts.

The D-2 edge (the thin one) suffered greatly from this test, even though it was much harder. The edge not only indented where there was contact but likewise, chipped out around the impact area.

The INFI edge (the thick one) reacted exactly as INFI was designed to do, in so far as it did not chip out and close inspection shows that the INFI actually absorbed the impact by denting and not chipping.

The final word, (hopefully). If these two knives would have had their steels reversed with the corresponding hardness, then the results would have been almost exactly the same as those listed above. The thick edged D-2 blade would have dusted the thin edged INFI blade. It is to be expected. It is important to note, however, that an INFI edge, in our tests, shows greater resistance to chipping than any other quality cutlery steel. INFI will indent when other steels will chip. This offers much less edge damage and greatly reduces the odds of experiencing a catastrophic failure.

So, why, in the above photos, did the INFI blade smoke the D-2 blade?. . . . Superior steel?. . . .Superior heat treat?. .. . . .Superior design? . . .. . Nope! Just a thicker and more obtuse edge bevel. .. .That’s all. . . . .A thin edge of any hardened steel will lose when impacting a thick edge of any other hardened steel. .. .. . . .So, what does it prove?. . .. .. ..It only proves what was stated in the opening thesis. . .. It only proves which knife has the thicker or more obtuse edge.

Yours in nuclear testing that proves nothing,

Jerry Busse


[This message has been edited by Jerry Busse (edited 04-25-2001).]

 

[Wulf]

Actually, such tests prove one other thing - that "performance" is subjective and almost anyone can be a sucker when information is lacking.

Thanks for sharing some more of your knuclear knife knowledge.

 

[Burke]

If I remember correctly from geometry, an acute angle is actually thinner, while an obtuse angle is thicker.

 

[Cliff Stamp]

First off I have to say excellent job on the edge profile of the D2 knife, that looks like it would cut exceptionally well. Secondly, I would disagree slightly concerning the interpretation of the results. While I would agree that the geometry of the edge is a major factor, hardness and durability are also factors.

The reason the hardness isn't a controlling effect in this case is because ratio of the relative hardness to the relative geometry is basically zero. This number would give you an estimate (a very rough one) of which would be the controlling factor.

For example if you did a controlled cut (using a vice) with two knives with a 45 degree bevel and a ten degree bevel, the difference in geometry is so huge that it will totally swamp out a few points in RC.

However if you did it with a 45 RC and 60 RC blade with a 17 and 15 degree bevel, then the RC would most likely be the controlling factor. Now the magnitude of the ratio has flipped (its >1) and the RC effect swamps out the geometry effect.

In general I would agree that all cutlery steels are of similar hardness so geometry is going to be the major factor, however there are blades such as Boye's cobalt that are less than 40 RC. These will indent very readily compared to 60 RC steel blades. As well of cource consider the non-metallic blades both G10 like and Ceramic. These take the range of hardness well below and above steel blades respectively, and thus the geometry won't have the same kind of dominant effect as it did in the above if you do cuts with these and an INFI blade.

For example I have done heavy impaction work on some Cobalt alloy blades (just put them in a vice and hit them with a steel bar) and have seen them indent readily as compared to steel blades with similar and even more acute geometries. The difference in RC here is about 15+ points so it has much more of an effect on the results that the difference in the blade you used which was only about 4 RC.


Note the critical part being a *controlled* cut, if you slam them together by hand you are introducing a totally difference stress on the edge as people can't cut with the same precision as machines and after the blades make impact there will be twisting as the force will not be applied in a consistent plane.

It is easy to see this for example by cutting a bolt in half in a vice with a knife and taking a similar bolt and pounding the knife through it with a hammer. Just about anything can do the former (with a soft bolt I have done it carefully with kitchen knives) but the latter will readily take huge pieces out of blades with poor ductility and/or low impact resistance.

I have blown pieces out of ATS-34 and VG-10 blades in this way (pounding them through a steel bar) that were thicker edge than a carbon steel blade that could do it with no harm (cheap 1095 Ontario machete), the relative ductility and toughness in this case being far greater than the relative hardness.


You can see this in the above as the INFI blades shows a mashed in cut whereas the D2 blade has fractured holes. Similar to the comments about RC and geometry, toughness can be a controlling factor as well depending on how its relative magnitude compares to the relative hardness and relative RC.

As another example, I have done chops into 5160 blades at the mid fifties in RC with much harder blades that have much more obtuse geometries. Because of the huge difference in ductility and toughness in favor of the 5160 blades it sustained less damage even though it was softer and more acute (a HI khukuri and a MD TUSK for example, I can't remember which one I think it was the first, I have done it with other blades as well).

So I would say that you can draw conclusions from it, but you need to consider all the factors. In the trivial case, if one of the relative aspects is *much* greater than the others then it is straightforward to note that it will be the controlling influence. In the harder case, when all are similar in magnitude, predicting the outcome is not as easy.

Nice job on not being afraid to damage a blade either and posting a picture of it in a public forum.

-Cliff


[This message has been edited by Cliff Stamp (edited 04-25-2001).]

 

[Cobalt]

Well, I have to say that when I tested the really obtuse edge of my light saber against the rolled edge of my excalibur sword, I found that the excalibur just sizzled and didn't chip or indent. However, my light saber just kept on getting shorter and shorter until it was only a cigar lighter. Oh well, so much for new technology.

Seriously(if that is possible), I think that toughness, hardness, and microconstituents all play a role along with edge geometry, but I would say that edge geometry is the controling factor, especially when you are talking rolled edges, which are considerably thicker than other edge profiles.

 

[Jerry Busse]

Burke,

Why, whatever are you talking about?. . . . Obtuse and not acute?. ... . .I don't see where I said acute. . .. (psssstt, never mind the footnote, " This message has been edited by Jerry Busse" . . it means nothing!

Thanks for the heads up on that by the way. We normally do not use the terms acute and obtuse but rather refer to these varying angles as "steep" and "shallow" . . . . boy, I try to use a technically correct term and I blow it. I'm having flashbacks to h.s. geometry. . . . NOOOOOOOO!!!!!!

Yours in nuclear geometry,

Jerry Busse

 

[Jerry Busse]

Cliff,

Well, well, well, I was hoping to lure you out and engage in a little academic bantering about these test results. Now that I've read your response I can see that that simply is not going to happen. I'm not exactly sure what you said but I'm pretty sure that it is wrong and I will be changing our warranty to reflect any and all points that you may or may not have made.

How's that for an academic butt-kicking physics man?

Yours in nuclear ratiotic magnitudes,

Jerry Busse

 

[Fire Horse]

I am courious what needs to be done to re-condition a knife that has that kind of damages to the edge? One obvious thing would be that the original shape of the blade could change.

------------------
Ed Woo

 

[Jerry Busse]

As for the INFI blade, a few strops with a ceramic stick will remove the bent over steel and unless you're worried about the cosmetics of the edge, this small amount of deformation should go unnoticed while using the blade. However, if you do want to move past this, it will require using a stone or simply send it back to the shop and we will do it for you at no charge.

Jerry Busse

 

You horrible, horrible man! How can you do that to such a nice knife. Got anymore of those shop knives laying around. I'll take'em.

 

[Jerry Busse]

Ryu,

I know where you can get a partially serrated one. . . .really cheap.

Jerry Busse

 

[Burke]

You're welcome Jerry.

Need an office proofreader? Former English major will work for knives.

 

[Cliff Stamp]

Jerry Busse:

<font face="Verdana, Arial" size="2">I was hoping to lure you out and engage in a little academic bantering about these test results. Now that I've read your response I can see that that simply is not going to happen.</font>

Nah, I am not the type to engage in a long drawn out argument, especially over the 'net.

<font face="Verdana, Arial" size="2">I'm not exactly sure what you said</font>

Most of what I write is composed under the influence, it is somewhat easier to decipher if you read it in the same state of mind.


-Cliff

 

[SALTY]

I think the academic bantering between Jerry and Cliff is ah, cute.

 

[Ralf]

Doing this kind of "test" has the same performance significance like hitting a diamond (hard and fragile) with a hammer (soft and ductile). Since the hammer will always destroy the diamond that can only mean that hammers are superior to diamonds. Hmm, maybe I should get my wife a nice hammer for her birthday.

[This message has been edited by Ralf (edited 04-28-2001).]

 

[Cliff Stamp]

To clarify a little concerning what I wrote in the above. If you see this "test" performed odds are you are being sold a line of hype. The first thing you should check as Jerry noted is the edge geometry. If the damage is constrained to the edge bevel then see if the blade that got mauled has a more acute edge grind. If the damage actually goes past the edge and knocks a big chunk out of the blade then you also want to see if there is a big difference in how thick the blades are behind the edge.

In addition there are lots of other factors that can influence the result including the method used. This is a very complicated aspect. It is very easy to do something that looks very similar but is actually very different that what you think is being done.

For example, I can take two identical knives and pound both through a small bar of mild steel and have one come through in very good shape and one get completely mauled. The outcome will be strongly influenced by how I am holding the knife and how and where on the blade I am hitting it when driving it through the bar.

There are also a number of tricks that are used to keep you from figuring out what is going on. For example you maul the blade first and hand it to the individual you are trying to "sell". Odds are that they won't even be looking at you when you are using the other knife as they will be distracted by the mauled knife plus you can distract them even more by what you say, directing them to the broken knife by commenting about various details.

Plus it is very likely that they are not going to have carefully watched you in the first place as you are not really doing anything that complicated and again engage them in conversation before you start. If you can do it without looking at your hands then all the better as the customers eyes will usually follow yours. Your manner and attitude have a huge amount of influence. Be open and friendly and try to engage them in conversation constantly.

Bottom line if someone is trying to sell you something they obviously have a huge bias, generally you disregard anything they have to say about performance -except- if they will guarantee the performance which means they must allow you to try it for yourself. This is the easist way to cut through all the hype. Just simply ask them if you can do it for yourself. And more importantly can it be done with the same blade you are going to buy not some demo model which may be a very different beast altogether.

-Cliff

[This message has been edited by Cliff Stamp (edited 04-29-2001).]

 

[Crayola]

Jerry:

Youa re the only knife maker/company guy that I know of who has gone out of his way to take 2 blades and do a test to prove nothing!!! That is great!!

Well, you actually taught us about edge geometry, and clearly that isn't nothing. Thank-you.

------------------
"Come What May..."

 

[medusaoblongata]

Jerry - any chance we could get you to reprofile a portion of the Battle Mistress blade so it matches that of the D2 blade and then do it again? I'm curious to see how the blades would look after the same test if the edge geometries were identical.

------------------
Jason aka medusaoblongata
-----------------------
"Is not giving a need? Is not receiving mercy?" - Thus Spoke Zarathustra
"Cutting his throat is only a momentary pleasure and is bound to get you talked about." - Lazarus Long
"Knowledge is not made for understanding; it is made for cutting." - Michel Foucault

 

[Strabs]

Better yet medusa, Jerry needs to fit brother Bubba with a new set of convex ground INFI incisors and give him the D2 blade to chew on for a while

Now THAT would be an impressive test...and I would also expect some extraordinary results

 

[Cobalt]

Another very interesting thread done a long time ago. Cliffs Techno babble even confused Jerry, no surprise there though

enjoy:thumbup: