Edge Retention/Rolling Test Stand

[KnifeGrinders]

Yes Mark, it is unlikely that edges soften due to a momentary overheating; it was just a horseback guess, failing any others.
Whatever causes this, if we only had a clean and quick test to spot the edge that will roll more readily before we put the knife to use or hand it over to the customer.
When we have this test, we can catch what in the sharpening process causes it, and then make a more plausible guess.
Till then it will be from overheating, just because humans are intolerant to uncertainty.

What this device is promising to be, compared to the rope cutting, is like BESS edge sharpness tester compared to CATRA edge longevity tester - or in one word, not the same.
I also put my hopes on it in quick detecting a wire edge without dulling the edge; the knife community think we've solved the wire edge problem, but it has re-emerged in super steels.

[grepper]

I was discussing building a contraption with Mr. Mike and was getting stalled by the details.  Somewhere along the way he most perspicaciously said something to the effect that if you think something is going to work and you reach a certain point, you just have to pull the trigger, build the thing and see how it pans out.

That is very good advice.  As the saying goes, a journey of a thousand miles begins with the first step.

At this point it is not clear exactly what this device will test for or what its impact on a blade will be.  Will it reliably roll an edge?  Will it mash an edge?  Will sharpness readings correlate with edge retention?  As Mr. Mark questions, does it have anything to do with edge retention or is that a completely different issue?  Will it provide results indicative of how heat produced from grinding impacts the edge?  Will it provide actionable or at least interesting data?  Yup, those are the questions.

Like edge sharpness testing, the data it provides may be specific rather than general.  Sharpness testing does not inform as to the hardness of steel nor edge retention, but the data provided is extremely valuable.  It might be a successful and useful device, or possibly a total and complete waste of time flop.

While interesting and up to a point worthwhile and necessary, discussing something to death leads to inaction masquerading as action.  I have little doubt that the device will do something.  The exact ramifications of that something is yet to be determined, but at least this will be some-thing and IMHO a step forward.

[Mark Reich]

Well, in that case, Mr. Ken nailed it.

If you want to precisely affect an edge in a repeatable fashion, there is a carbide milling bit that will work and remain unaffected, no matter how you choose to affect the edge or detect a wire edge IMHO.

[grepper]

Mr. Mark exclaimed, “On the other hand, you have another, more popular way to degrade edges. Cut Stuff.”

If edge retention is what you are looking to test, I have always thought, and still do, that this makes a lot of sense.  Cut stuff.  It works.  It has to work.  It makes sense that cutting stuff most closely mimics, if not actually is, real-world use of a blade.  And, is not real-world use the most applicable, if not the very reason for edge retention testing?  Mr. KG’s pig plant data is a perfect example.  If that is not real-world edge retention testing nothing is.  While it is not used for edge retention testing, one of the main advantages of BESS sharpness testing is that it tests edge sharpness by, guess what… cutting stuff.

What is missing in the cutting stuff edge retention testing world is consistency of the material being cut.  Some folks cut rope while others use cardboard, or whatever.  The BESS scale would be worthless if it were not for the consistency of BESS test media.  What is needed for edge retention testing by cutting stuff is a universally agreed upon test media.  

Of course there are other factors such as pressure and length of cut, etc. that would need to be standardized, but that’s not really the point.  To me at least, as far as edge retention testing goes, cutting stuff just makes sense and what I intuitively consider.

That said, it may turn out that data gathered from a pressure test may actually correlate to edge retention.  Mr. Mark, I’m guessing that you would concur that if that were to be true and reliable, that it would be very cool and welcome considering the reduction of effort required.  I know that I find the idea of spending hours testing by rope cutting daunting.  There is one big difference however; edge retention data arrived by cutting stuff is direct, but pressure data would be inferred or indirect.  

To me, the test stand would simply be a hardness test that might be useful in testing if edge hardness is reduced by heating or comparing the hardness of various blades.  Kind of a poor man’s Rockwell test, yet with the ability to test edge hardness which is something that as far as I know cannot be achieved with a Rockwell tester.  If it ends up that edge retention assumptions may be gleaned from such data then great, but that is yet to be determined.

[KnifeGrinders]

"Cut stuff".
Oh friends, if only it was that straightforward.
In the previous thread I wrote how I assumed that a knife with a microbevel that showed better cutting performance on cutting rope should outperform at boning in a meat factory - only to prove that assumption is the mother of all f*ckups.
It performed worse than an identical knife without the microbevel.
Repeated on the second day, still the same.

To follow the "cut stuff" approach, the stuff must be matching.
From what I've learned, we cannot generalize rope cutting onto other areas.
I now doubt that a champion knife in the rope cutting competition will be favored by a Chef slicing in a restaurant.
It will only be appreciated by a rope cutter, if there is such a paid job.

Yes, rope cutting does provide us with information about the edge wear resistance, but in no special advantageous way.

[grepper]

Yup.  That's the problem with edge retention testing.  It gets very complicated extremely quickly.  I think that general edge retention can be tested for, but, and the reason I keep using the term "real-world", is exactly what you say; edge retention is only really measurable in the environment and under the stress conditions that that the blade will be used in.  

It gets so complicated so quickly that it almost seems a futile pursuit, but that leads to doing nothing.  Maybe the answer is that it's only worth bothering with if testing is specific to the use of the blade.  I don't know, but that would not surprise me.

[Mark Reich]

Thank you, Gentlemen. From my perspective, I think my reasoning has followed Mr. Grepper's pretty closely, but I'm starting to get used to being wrong.

Let me preface this with a disclaimer, please. I'm sorry that I don't understand exactly what you're trying to accomplish, but I truly only wish to help accomplish anything, anytime. Every time.

I only suggest 1/2"- 3/4" manila rope because of it's individual uniformity and abrasive quality. It doesn't have to be exactly the same as the next brand of rope. Just get 100' and you can do a lot of testing. When you pair it with the accuracy of a BESS machine, you might only need to make ten cuts. 

I've been cutting rope for many years. I've asked around, and rope doesn't care what type of edge you provide. It has to be as consistent as dicing hogs or dissecting carrots.

Mr. EOU, before you go through the trouble of building a machine as you describe, wouldn't it be just as easy to use the weight of the knife, and draw it across whatever you have that's hard?

Maybe start with an ordinary water glass, as ordinary glass is amazingly consistent at about RHC 54, or Mohs 6.5.

I know the weight of the blade would be a variable. Maybe just keep using the same knife or knives in the same manner. Maybe tape some quarters to the blade to add consistent weight.

Maybe use a DeWalt HSS drill bit, which would be harder, but probably the same hardness no matter where find one. It would even roll on a hard surface to eliminate galling, if that's a consideration.

If you need something really accurate, precise and homogeneous, Wilson Rockwell Test Blocks are about the limit.

Am I even close?

[grepper]

I don’t think there is a right or wrong here.  Just different ideas on how to accomplish something.  I believe the first impetus behind the test stand is to try a test if edge heating during sharpening changes the hardness of the edge.  More of a hardness test than a direct edge retention test.  

As long as pressure and maybe speed was standardized, simply dragging a blade across a drill bit or Rockwell test block seems like a very quick, simple and probably quite accurate test.  It would more accurately mimic real-world use than a straight down static pressure test.  But I don’t really understand either exactly what is being tested for.  Strictly hardness?  Edge retention?  Flexural bending resistance?  All three?

My first inclination is that, up to a point, harder steel will always have better edge retention than softer steel.  How could it not?  But I don’t see edge retention testing’s main purpose to determine if one blade is better than another, but rather to help determine what grinds, initial sharpness and blade geometry perform best in a specific environment.

Ideally, edge retention would be measured after a blade has been used for whatever it is going to be used for.  That’s especially cool if indeed the blade has a single mission in life.  But what for a general purpose blade?  A blade that may live to open a can, cut a stick or some rope or open a box?  For that you might as well just see how the blade performs cutting rope.  I suspect that would provide amazingly appropriate results.

It looks to me that the test stand performs a compressive strength test.  But, a knife edge may roll before being crushed, and that would throw flexural or bending data into the mix.

I have the feeling that the test stand is more of device looking for a mission, than a mission looking for a device.  I’m pretty sure it will do something and spew forth some sort of data.  The most useful application of that data may be yet to be determined.

[scott.livesey]

the testing machine looks interesting for numerous reasons.  using it as shown, it could show that O1 at Rc64 with 10 pounds applied chipped while 1095 at Rc55 rolled.  I could also see it used to test different cutting board materials.  results might show end grain no damage; edge grain no damage; HDPE no damage, glass edge rolled.  i like the idea of only two variables in play here, the hardness of the block and the weight applied.  this should make repeatability very high.
as far as just cutting stuff, I have taken the Japanese approach in my kitchen.  I have very thin very hard blades that excel cutting boneless protein and soft vegetables.  when it is time to cut carrots or winter squash or bony meat, out comes the cleaver or heavy chef's knife.
cutting rope or cardboard just shows what edge works best for rope or cardboard.  as KnifeGrinders found, a edge that excelled in rope cutting failed slicing raw protein.  
I think many makers have forgotten that the blade is just a small piece of the puzzle as far as what makes a good knife.  knife users not infected with the steel bug are looking at fit, finish, comfort in use, balance, how well a folding blade locks, and weight. make a knife that scores high in each of these categories and the average user could care less if the blade is 3Cr13 at Rc55 or S125V at Rc65.  now that the temperature is higher than 30F for the first time in over a week, I will go to shop and see what materials I have on hand to make such a tester.

[EOU]

We don't expect the edge to crush but rather to roll (bend) to one side or the other. We understand and appreciate fully the theory of crushing in light of how the test is to be conducted but our experience indicates that sharpened edges act otherwise if allowed to do so. This is demonstrated by the ability to return rolled edges to at/near their original sharpness levels by simply straightening the edge. So what do we mean by "if allowed to do so"? It is easy to imagine that the edge would be become somewhat "stuck" on the surface of the hardened rolling strip once the weight of the piston/edge is released. If the edge is to "roll" then the body of the knife has to be allowed to move laterally at least a few thousandths of an inch. In other words we need a little designed in "slop" in the piston guide assembly to facilitate this lateral movement. This may be exactly how edges are rolled in the real world. The edge bites in and the knife blade moves to the side.

For us the test for success is going to go like this; we measure a sharpened edge, we place it in our test stand and intentionally roll the edge 50 - 200 points and then return the edge, via edge straightening means alone, to at or near it's original sharpness level. If we can do that then we will likely believe that we have constructed a viable test apparatus.