Edge Retention/Rolling Test Stand

[EOU]

We're running this up the flagpole here because we're interested in your input so please, input away.

The premise here is that edge rolling is a major contributor to dull edges and edge longevity (retention).  Edge overheating during the sharpening process is probably one of these contributing factors that we could all agree on but how much of a problem is it? A little, a lot or a whole lot? If one sharpening methodology seems to indicate a very measurable effect on edge rolling does another methodology effectively mitigate it? Of course there are many other contributing factors that could be tested for as well and we won't try to enumerate them all here but, of course, initial sharpness level, steel hardness and blade geometry come to mind readily.

One thing that we have absolute confidence in here is the ability of our instrumentation to measure the effect of edge rolling. We can't tell you, in inches or degrees, how much the edge has rolled but we can measure its effect on edge sharpness with great certainty. But that what's it's all about for all of us here isn't it? How easy or difficult it is to cut through something.

So we propose to build a test apparatus. A test apparatus that will perform one very simple test; how much did an edge roll expressed by it's decrease in sharpness? We propose to measure the sharpness level of a particular location of a prepared edge then lower,very carefully, that edge onto a narrow strip of hardened steel and then measure again to obtain an indication of how much the edge edge rolled as a result of the process. We will be able to add loading (weight) to the process should that prove useful. 

So there you have it! It's a simple test stand to build and if you guys think that it could deliver useful information then we'll build it. We'll test the edges we create and we'll test the edges you create if that's how you want it. If you have thoughts, design or otherwise, we'd like to hear them.  Please keep in mind that we are testing for only (1) one factor with this test instrument, edge rolling. We do not intend to try to define, with this device, how much better (or worse) a toothy edge slices than a polished edge  or any one of a myriad of other questions we'd like to answer. 

   

[grepper]

I think it's an excellent idea.  We have about exhausted speculating about the impacts of heating during grinding/honing, and it seems the only way to really move forward is to actually do some testing and see if our ideas can be substantiated with empirical data.

Personally, this is something I would like to understand clearly.  At this point I can only speculate as there seems to be only a modicum of available data.  

I'm always surprised that this, as well as a lot of the aspects of knife sharpening have not been completely figured out.  I suspect the reason why is that the advent of edge sharpness testing is only a fairly recent innovation.  

If we can actually provide demonstrable data here, not only would it be very valuable to the sharpening world, it could be a real game changer.

[Ken S]

The design seems clever; simple and direct. My first thought upon seeing it is that it looks like a descendant of another clever, simple, and direct testing device, the legendary KN-100.

Kudos to the EOU design team!

Ken

We certainly have enough Tormek users to provide cold sharpened test samples.

[KnifeGrinders]

That's what I call an idea of genius.
At the knife weight, this device should be able to help detect a foil/wire edge, and under a loaded weight somewhat predict edge retention for the steel tested.
If the relation between the edge apex rolling in this test and edge retention proves tight, it will be a breakthrough.

What steel do you plan to use for the "strip of hardened steel"?

[EOU]

Well thank you very much KG. You're seeing the test as we do. 65 HRC steel is readily available. We considered glass as well. What do you suggest?

Ken, hadn't thought about it but you're right. I guess we do get stuck in our own little groove. We may call on you for Tormek examples if that's OK. John Lucas's small chunks of steel would be ideal.

[KnifeGrinders]

The most convenient design I see is to have enough room to place a PT50B into your impact tester stand under the blade:
- take a baseline sharpness score;
- replace the ATF with the impact bar, placing it straight on the PT50B platform - lower the knife to contact (and for rolling test also apply 500g - 1 kg load);
- return the ATF and take the score.

Such a design makes it salable as an adjunct to your current testers.

Not sure about 65HRC for the impact bar, as I just got half a dozen custom knives from a knifemaker at 63-65HRC to sharpen.

[Ken S]

How about carbide? A solid carbide quality quarter inch router bit like the Whiteside bit shown in the link would be cost effective.

http://www.carbideprocessors.com/60deg-v...gJxm_D_BwE

Ken

[Mark Reich]

I've been wondering for ages why this couldn't more easily be a one step test, as in an edge denter, somewhat like a simple Rockwell device. After all, I truly believe the subject at hand is specifically measuring edge hardness now. Edge rolling is a different subject altogether IMHO. Maybe I don't understand what you're trying to do.

Trying to accurately roll an edge might be very difficult, and subject to the differences in type of steel. There is a term for a particular steel's predisposition to roll, called "edge stability". It's not a new term, I've heard it thousands of times, so I assume someone has done some homework on it. I think it's a known characteristic of different types of steel, Besides edge geometry.  

If I were trying to accurately roll an edge, I wouldn't have the edge 90° to the hard surface, because the chances of rolling one way, then arbitrarily flatten and roll the other way would lead to imprecise results. Of course the test device would have to be more substantial, to mitigate torque, but I don't know exactly how else you could roll an edge precisely and consistently. I'm also unsure what affect a precisely rolled rolled edge would have.

On the other hand, you have another, more popular way to degrade edges. Cut Stuff. I've cut enough rope to have a pretty good understanding of the accumulative affect of normal wear. This takes nothing more complicated than simply getting used to cutting rope. I know it may seem like an oversimplification, and a lot of effort, but I know it works. 

I hate to think of how much time and effort I've wasted cutting rope until the knife gets dull, compared to how simple it is to make a hundred cuts and measure the change in BESS units. That's Truly what I thought Edge Retention Testing would consist of. Just rope and a BESS machine. Edge retention probably has much less to do with rolled edges than simple wear, as long as you aren't cutting on glass or dishes or whatever stupid people cut on. 

I've actually done a fair amount of testing using this method, and I've been waiting for about 9 months for someone else to practice this simple procedure. 

I must say, I don't have the foggiest idea about flash temperatures of thousands of degrees F for .000001 second. That's completely beyond my sense of reason, or the reason of anyone I know who has sharpened thousands of blades. For every page written about flash temperatures such as this, we have a decade of whole world, real life experience.  

Please consider this. I'm not talking about extraordinarily limited, Laboratory Induced Micro-Theory here. Facts. Probably Trillions of sharpened knives. As I understand, this Theory is not limited to power sharpening, so we are in range of every single sharpened edge the world has ever seen.

I'm sorry, but I'm going to go with what has been positively known for centuries, not someone's pet lab theory. Seriously, how much information are we basing all this hubbub on?

There is a very simple rule by which we've all been playing for hundreds of years. I don't understand why we need to reinvent the wheel. If the edge doesn't change color, everything's groovy. It's worked so well, no one has been able to figure out something more accurate to date. No One. Ever.

If you want to know if you're affecting the hardness of an edge, feel the blade with your fingers. If it burns your skin, it may be 300°F, and you need to dunk it in water and do something differently. Like simply not using as much pressure, or traveling faster, or changing belts. I positively guarantee 300°F for a few seconds is absolutely meaningless. I state that as a matter of fact that has stood for centuries.

Here's one last way to prove beyond the shadow of doubt that this manner of softening steel is ridiculous. Cumulative affect. Sharpen one blade a hundred times and see if you can tell the difference. You certainly wouldn't be the first to sharpen one knife a hundred times, and I simply have nothing to show it's ever made any difference at all.

Or I could be wrong. Like everyone else.

[me2]

Is it necessary to use material harder than the knife edge?  I could see a simple A 36 or 1018 steel rod being sufficient, depending on load.  However its also possible that it would have to be moved after each test, if the edge were to make an indentation under high enough load.

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One other thing to consider would be the ability to see where edge deformation is reduced or eliminated as a function of edge angle, when compared on the same edge.

[Bubby]

I like and agree with what is being tested for here. My experience tells me that the the primary source of dulling is due to rolling.  At least on a short term time scale. I think that there is a reason that a million butchers and meat cutters hold a boning knife in one hand and a smooth steel in the other. This thought is based on normal use and not someone who is try to cut stacks of sandpaper sheets into pieces. Seems to me that if the steel is better and/or the blade is sharpened using good techniques that the edge is going to be more resistant to rolling. Is this the end all/be all of edge retention testing? I say no but I think that it is going to tell a very important part of the story and maybe the most important part.

Me2 makes a good point. I don't think it's necessary to use hardened steel. I know that a piece of soft steel will knock the #$$# out of an edge. As he says, you might just have to shift the piece after each test. Or, use something very hard and don't worry about it. 

Here's a thought though. Use a soft steel strip and see if the edge does leave an impression. If it doesn't but does roll the edge significantly we can ponder why. We might not like the conclusion we come to.