Edge Retention Testing and Analysis

[db]

I'm not sure if I remember. Did they only do this test 1 time? Are the results and data they got repeatable?

 

[Cliff Stamp]

... it has been shown by others, one of the more notable being Tim Zowada, that a harder blade requires more force to break, and it takes less to permanently bend a softer one. ...

This is basic metallurgy, opposing this is just absurd. The fact that knifemakers have to actually demonstrate it shows just how bad the propoganda influence is in the north american market.

You might as well start with a blunt SV90 blade and then say how your FFD2 blade cut so much more rope.

Yes, that is why I asked how they would feel about the same type of comparison which was inverted where the FFD2 blade was much duller initially and then outcut by 420HC. THis would in fact be an easy test to conduct with both steels given the SAME sharpening method.

... I see no functional reason for a knife to have a hardened edge and unhardened blade.

Unhardened is just silly, you can bend unhardened even 1/4" still trivially, you might as well use mild steel. However try to sell that knife and see what happens. It will bend all over the place of course, just weld on a strip of hardened material to the edge.

No, I think using a more suitable steel and stock size is a better idea.

That is why they are there.

-Cliff

 

[gator68]

Unhardened is just silly, you can bend unhardened even 1/4" still trivially, you might as well use mild steel...

Apparently, the FFD2 knives are made this way -- FF hardened edge, unhardened back. This seems to be a limitation of the technology.

Many ABS knives are made this way. This is done deliberately to get a great looking hardening line. Great looking, but not functionally optimized IMHO.

In my opinion, a serious using knife should be hardened all the way through. The smith can go back and do differential tempering if he wants, but the whole blade should be hardened as a minimum.

 

[gator68]

I'm not sure if I remember. Did they only do this test 1 time? Are the results and data they got repeatable?

If you go back through all of the posts, you can find where they posted a link to an excel spreadsheet. It looks like they did the same series of tests about two times on each knife.

 

[PatriotDan]

I've never heard of unhardened spine with differential heat treat. It's been from mid 40s to low 50s as far as I've read.

 

[Wayne G.]

Gator wrote:

“Apparently, the FFD2 knives are made this way -- FF hardened edge, unhardened back. This seems to be a limitation of the technology.”

In my opinion, the width of the hardened portion of the FFD2 blades will be adequate for a lifetime of use. A serious use hunting knife I made in 1980 (D-5) has been in nearly constant use by a customer and has field dressed and skinned 57 big game animals. The knife has also been used for processing the meat on some of the animals. The total wear on the belly of the blade is about 30% the width of the hard portion on the FFD2 blades. If all the initial tests of edge holding ability hold up, the FFD2 will need to be sharpened something like 25% (or less) less than the D5 blade and perhaps as much as 15% less than is necessary for standard D2 at 60Rc.

I'll try to answer the opinions on soft back and temperlines in a separate thread. (If I can figure out how to get one started.)

Wayne

 

[Kohai999]

Gator wrote:

“
In my opinion, the width of the hardened portion of the FFD2 blades will be adequate for a lifetime of use.

I'll try to answer the opinions on soft back and temperlines in a separate thread. (If I can figure out how to get one started.)

Wayne

Thanks, Wayne.

HardHeart, you instigated massive thread drift. A continuation of the hard edge/soft back discussion should be continued in the thread that Cliff originally started back down aways.

This thread was started so the BYU boys and Cliff could get to some accord concerning testing methods.

Are we there yet?

Best Regards,

STeven Garsson

 

[Broos]

This is all a very big IF. There is no evidence that the Diamondblade people have done anything like this. They presented results where for some reason their blade had a much higher initial Ci, then cut until a fixed C was reached. Despite having the same initial sharpening treatment, they did not seem interested in understanding or explaining why the FFD2 was so much better initially. This different starting point has a big effect on the results. You might as well start with a blunt SV90 blade and then say how your FFD2 blade cut so much more rope.

I agree it is an "if" - but until it is tested, everyone needs to decide for themselves what is the bigger "if". Would the slicing ability be equal for all steels given equal geometry and sharpening? I am more willing to assume no, than I am to assume yes. But I do agree that the order of difference here seems large.

If you are going to assume that they had edge problems that caused Ci's to be different, then you must also assume that the these edges, where some had problems and some didn't, would all test to the same REST values.

My point is less to discuss their test, and more to figure out what test those who object to this test methodology are going to run. I can imagine some uses of the alternative methodologies, but I do not see an advantage for the average user, and I do not think I will ever buy into a test with blades of different steels with different geometries and sharpening being very useful.

There is nothing wrong with questioning results. And I agree that adding examination of the edges with an experienced eyeball would be a nice improvement to their testing. Even more interesting to me would be to run test runs at varying geometries and sharpening. But it doesn't make sense to me to want to throw out the whole test methodology, and not be able to offer a clear alternative.

 

[Cliff Stamp]

In my opinion, a serious using knife should be hardened all the way through. The smith can go back and do differential tempering if he wants, but the whole blade should be hardened as a minimum.

Generally yes.

I've never heard of unhardened spine with differential heat treat. It's been from mid 40s to low 50s as far as I've read.

Edge hardening is fairly common common.


-Cliff

 

[cds4byu]

No Chuck Buck did himself directly (from memory) "We gre bored waiting for the knives to blunt on the CATRA machine, but in REAL LIFE it is otherwise." He specifically mentions the effect of forces on the edge which blunt by a mechanism other than wear. He even notes the exact cause (correctly) and makes it public. This was years ago on the forums.

Is this math?

...there is almost always more than one way to perform a numerical calculation.

This is just math, you state the judgement criteria and it isn't opinion. No more than stating that if you are looking for a steel to take shock then S7 is better than T15.

Cliff, it seems like everything you want to state is math, and everything anybody else wants to state is opinion. I'm still waiting for the reference by somebody other than Cliff.

...you're admitting that there is a subjective component when deciding how to transform the data to derive meaning from it.

This again would be math. For example you can transform a function to make it faster to calculate (less numerical operations) or more robust (less parameter correlation). These again are not opinons.

Until there are numbers attached, it's not math. I suggested that there were alternate ways to do analysis, and you ridiculed me for it, because "it's just math; it's not subjective". You still haven't shown me math -- just opinions and your assurance that it's math.

I showed years ago how you can make a blade progressively lose slicing aggression while maintaining a high standard of push cutting sharpness. It is strongly dependent on the carbide nature vs the abrasive.

Could I have a reference, please?

As an aside, if someone was to perform an evaluation on your product would you want them to go forward publically with the result if they were found to not be in your favor and yet had a number of concerns such as the above which could in fact be a misleading conclusion based on less than optimal methods?

As long as they were open in their testing and analysis methods, I'd be fine with it. But if they wouldn't give me the necessary details to replicate their testing and analysis, I'd push to get them to disclose the methods.

As noted, I described the physics underlying the model in the same page as the equation is first described.

If I gave that description of the physics of any process in a paper for peer review, I'd never get it published. The only comment that I could find that had any basis in physics was "The work done on the knife equals the work done on the cut media." Everything else is stated without either proof or justification.

I don't speak german either and have only a brief working outline, as noted I am doing the survey now. I gave you a couple of key authors, did you even to a search on them and read their relevant papers?

No, because I don't know which papers you consider relevant. And I'm trying to respond to your stated concerns.

OK, so please let me know if I understand this correctly.

1. You perform edge retention tests to determine the sharpness as a function of the amount of media cut. You do this multiple times for a given blade.

2. Using the data from step 1, you calculate the mean and standard deviation for each x-axis value.

3. With the Levenberg-Marquardt method, you use a nonlinear curve-fitting procedure to fit your model (C(x) = Ci/(1+ax^b) to the data.

4. The fitting procedure gives you values for Ci, a, and b.

5. The covariance matrix (which I believe is the same thing you called the correlation matrix) contains data on the goodness of the fit.

6. If the goodness of the fit is adequate, you have a reasonable measurement of the cutting performance. If the goodness of the fit is inadequate, you don't have a reasonable measurement, and you conclude that the data isn't yet good enough to report.

Am I close?

Thanks,

Carl

I'm still waiting for an answer on this question.

Thanks,

Carl

 

[cds4byu]

Originally Posted by gator68
It doesn't look like the problem is "noise";

The actual measured data as I showed was perfectly fine and fitted by the model with well defined parameters. It was only when the calculations were performed on it which exploded the noise that the curve became undefined. It still fit the data fine as measured by the residuals, the noise was just so high that the curve was undefined, meaning too large of a range of parameters could satisfy the spread of the noise in in the data.

Would you please identify which calculations "exploded the noise"? Was it your calculations or was it our calculations? And which ones?

Thanks,

Carl

 

[cds4byu]

In my opinion, the width of the hardened portion of the FFD2 blades will be adequate for a lifetime of use. ...

Wayne,

I moved a reply to this over to the FFD2 thread.

The link is here

Thanks,

Carl

P.S. Did you have a good time at BLADE?

 

[cds4byu]

Thanks, Wayne.

HardHeart, you instigated massive thread drift. A continuation of the hard edge/soft back discussion should be continued in the thread that Cliff originally started back down aways.

You can find that thread here.

This thread was started so the BYU boys and Cliff could get to some accord concerning testing methods.

Are we there yet?

I think I've got it, but Cliff hasn't yet agreed with me, so I'm not sure.

Carl

 

[cds4byu]

I'm not sure if I remember. Did they only do this test 1 time? Are the results and data they got repeatable?

If you go back through all of the posts, you can find where they posted a link to an excel spreadsheet. It looks like they did the same series of tests about two times on each knife.

Let me clarify. Lots of tests were run, and the critical features were repeatable. Differences in test procedure were identified with time, so successive tests weren't exactly the same (i.e. there were differences in the mechanism used to hold the rope). However, the tests were exactly the same for each comparison set.

The data I posted represents a single test for each blade. The two REST values come from two measurements of the exact same blade in the exact same wear condition, so the noise in the REST measurements represents the repeatability of the REST test, not the repeatability of the wear test. The repeatability of the wear test has not yet been quantified.

Carl

 

[tnelson]

Cliff,

Now, after two weeks I think I understand your thinking. Let me summarize:

You first asserted that we presented:

........ really misleading and biased statistical analysis.

This was followed up on numerous occasions of you implying that we had "manipulated" the data in our favor.

Now in your latest post you state that:

Unless you are performing analysis by magic, all of what is done to data, filtering, smoothing, modeling, etc., is all calculations.

So, doing the math according to Cliff Stamp:

Manipulation=calculation, filtering, smoothing, modeling, etc.

Odd, but this is the way you have defined it over the past couple of weeks.

So, why is it that when you “manipulate” data, it is science, math, physics, and ABSOLUTELY correct. If anyone else is "manipulating" data, it is ....

........ really misleading and biased statistical analysis.

Over the course of the last two weeks, it is evident to me who is bias. In addition, your lack of willingness to fully disclose your analysis method for peer review implies that you are the one

... performing analysis by magic, ....

TN

 

[tnelson]

Cliff,

I spent a little bit of time over the weekend trying to find and review some of your hypotheses that you have "published" on your web site, and on Blade Forums. I failed to see the

.... physics of the mechanics of blunting.

In fact, there didn't seem to be much "science or physics" in your approach at all. Your approach is very empirical.

As Carl stated:

The only comment that I could find that had any basis in physics was "The work done on the knife equals the work done on the cut media." Everything else is stated without either proof or justification.

So, I'll ask again,

Can you please show/describe in physics or engineering principles the "physics of the mechanics of blunting". I have a hard time seeing this accounted for in the data/analysis that you have provided or directed us to on your web site.

Why are you so afraid of peer review Cliff?

TN

 

[Broos]

If I gave that description of the physics of any process in a paper for peer review, I'd never get it published. The only comment that I could find that had any basis in physics was "The work done on the knife equals the work done on the cut media." Everything else is stated without either proof or justification.

And even that stated "principle" is not entirely accurate. All the work done on the knife is not accounted for by the slice/cut and the deformation of the media required for the cut. Particularly with a human tester.

 

[tnelson]

Broos,

Now I have to deduct 10 points from both you and Dr. Stamp's quizzes because you helped him on that...science, physics, mechanics (stuff)... question.

TN

 

[Broos]

Like the annoying little kid who won't put his hand down and says "ooh, ooh, ooh" - sorry.

 

[gator68]

Cliff,

I spent a little bit of time over the weekend trying to find and review some of your hypotheses that you have "published" on your web site, and on Blade Forums. I failed to see the

In fact, there didn't seem to be much "science or physics" in your approach at all. Your approach is very empirical.

As Carl stated:

So, I'll ask again,

Why are you so afraid of peer review Cliff?

TN

I have to disagree here. Cliff has derived a fairly simple model for how a knife blunts. This is derived from the idea that the force applied to the material is the force applied to the knife edge; and that the force is "used" to blunt the edge and push material aside during the cut. From this simple idea, he comes up with a model -- a proposed relationship between sharpness and amount of material cut. He then tested this with data on tons of knives, and did repeated testing on the same knife. The model actually fits the data. Using the model, one can make comparisons between the performance of different knives. This is valid as long as you believe your model is useful and you take appropriate data that allows you to make meaningful fits to your parameters.

This is a perfectly fine approach to a problem in physics. I've done similar things to model particle detector performance. Rather than do first principle calculations of phonon propagation through gold-germanium interfaces, simple create a model using heat capacities and a "weak-link" between two heat baths. This turns the problem into a question of simple algebra, and captures 90% of the behavior. If that's all you need to know, then stop there.

As far as I can tell, Cliff has lots of data etc on his website. It's just not organized very well. I doubt he is trying to hide anything or avoid "peer review." You are free to show that his model does not account for the behavior you measured for example.

Here's a question for you TN -- why is the FFD2 blade so much sharper than the SV90 blade to start?