New testing session.

Broos, and others.... If you think about how little material supports a micron dimension fine edge and the volume of steel that is resisting the deformation (strain) and make some simple calculations then it is pretty obvious that the edge can fail either by bending or breaking with very little cutting force. This is a combination of compressive and tensile loads. If the cutting force is exactly down with no side loads then the edge is in pure compression. It can take a lot of force in this condition. As soon as a little side load or twisting (when the tester gets tired or loosed concentration) is applied then that is when I think failure happens. I am sure work hardening also plays a role since the fine edge is for sure moving around in the plastic range. What I am getting at here is that the way you cut makes a big difference. I think this can explain why we see some wide swings on results. If a fine edge breaks away or rolls continued cutting could restore it like a steel can straighten a rolled edge on a soft blade. This could explain loss of sharpness and then improvement as cutting continues. I also think that since hardness equals strength that the harder blade edge is stronger and can therefore cut longer as long as it does not fracture off. I also think that the high density carbides in some steels tend to act like aggregete in concrete and improve the stiffness of the edge. The longest cutting blade is going to be hard, at least RC 62 and be strong enough to resist failure long enough for the carbides to stay at the edge and resist abrasion. As the edge wears from abrasion then the area is increased and it tends to be able to take higher stress from the increased down load required to keep the blade cutting. High carbide steels will plateau out and cut at about the same force for a long time. Small differences in sharpening, edge angle, hardness (strength) will play into all this. Anyhow if you follow me what do you think? Phil
 
I think that all this lead to one conclusion - single test results may vary and so need to be treated statistically. This mean that I need to do same trick I am doing when I measure sharpness and take median from several tests. And this will give some more or less precise evaluation of steel edge holding.

And this is unfortunately mean a lot of work - repetitive and little boring. At least, with this clip I can keep my arm unharmed.

Thanks, Vassili.
 
Phil, you got me to get the calculator out. 20 lbs of force concentrated on a 1 micron wide (3.94E-5 in.) and 5/8" long edge. That's 20 / ( 3.94E-5 in. * .625 in. ) = Wow - that's 813,000 psi on that one micron thick edge! Undoubtedly this is an oversimplification, and the the bevel takes some of the load, but this is eye opening. Makes me wonder why that rope just doesn't part like the Red Sea when I cut it! Now imagine that edge hitting some silica or other hard substance common in many things commonly cut. With an electron microscope it would probably look like complete destruction. Feel free to correct my calc's! Thanks for the thoughts, Phil!
 
Vassilli, the day before yesterday I saw your test results of Juka Hankala`s hand forged silver steel blade. Pretty decent result I think. Thank you very much once again for your efforts. This data is very usefull to me because an year ago I ordered such a blade from Juka Hankala. Still gathering courage to make a padouk handle for my big Tommi blade.
 
Broos, you are right on. I wasn't sure how to figure the area supporting the edge. In any case an edge at 60 RC will have a strength of about 400,000 psi. The smaller the area the larger the stress so even with a little side load the strength is easily exceeded. What this means is that the sharper the edge the weaker it is. A "hair whittling) edge is not the optimum for cutting rope. A reason why sometimes results are over the map. I applaud Nozh for his work. He must have a very sore hand and wrist. I again have to go back to the premise the this is a test of knives, not steel. Yes you can get some rough ideas on wear resistance between steels but there are so many other variables that it tends to get lost. Hardness equals strength so unless we know the hardness of each blade then its hard to make good comprarisons. Here are some other variables that make a difference:
Blade shape-- A curved blade will cut better and longer than a flat one. The belly concentrates the force on the rope fibers so can cut with force and less wear over the long run.
Length of cut-- A longer slice distributes the force over more edge therefore less wear in any one place.
Hardness-- all ready discussed
Edge shape-- Flat grind is a wedge. A thinner wedge has a better mechanical advantage and less friction (drag). Hollow grind will drag on the flat to hollow transition.
Blade finish-- better finish has less drag.
A push cut-- causes less wear than a slice. So when cutting it is critical to get the same relation between a push and slice each time the rope is cut.

Some of these have more effect cuttting against a scale. But maybe helps to put some of this into perspective..... PHIL
 
Phil Wilson said:
Broos, and others.... If you think about how little material supports a micron dimension fine edge and the volume of steel that is resisting the deformation (strain) and make some simple calculations then it is pretty obvious that the edge can fail either by bending or breaking with very little cutting force. This is a combination of compressive and tensile loads. If the cutting force is exactly down with no side loads then the edge is in pure compression. It can take a lot of force in this condition. As soon as a little side load or twisting (when the tester gets tired or loosed concentration) is applied then that is when I think failure happens.
Click to expand...
I agree completely, Phil, and expanding on what you're saying, IMO this is critical to take into account during sharpening as well. When using a device such as a Sharpmaker the force being applied to the edge can be huge, and the finest edge can only be achieved by using the lightest pressure.

As came up recently in another thread, this is why doing things like stripping wire can be very hard on an edge, not only are the forces imbalanced left-to-right but the material being cut is hard to support and so winds up twisting and pulling in unpredictable ways.

All this factors into why, in my own edge retention testing, I stick with things like cutting cardboard or rope, materials where lateral stress shouldn't be much of a factor -- although with rope, the surface upon which you cut I'm sure can have a big effect.
 
I hope you guys will not only discuss this between yourself but also read some explanation I provided here. For example if you check my set up - there is not surface when I do cutting rope - edge ends up in the air (which is why I do way more cuts then Phill) as well as I explained why things like length and geometry of the blade does not really matter. As well as that I do "real world" cut - moving down and forward.

I did quite a bit of rope cutting - hair whittling edge as suitable for rope cutting as any other, it is just property of very edge indicating that sides in did form angle instead of being rolled, so it is perfect angle and it should not cut rope worse then any other edge and it does not.

With all this factors affecting performance we can came up with blades behaves obviously different and so may be all this factors does not really affect results too much. One way or another it is clear that ZDP-189 is premium steel as well as Dozier is really king of D2. while AUS8 shows average performance. I guess changing one or other parameter we may little increase performance, but may be not - it need to be proven by tests. So far I guess it is safe to say that AUS8 will never perform as good as Dozier D2.

Thanks, Vassili.
 
Vassilli, I was responding to Broos who brought up a point about edge deformation. Didn't mean to leave you out of the discussion. After all it is your thread to start. I was also attempting to explain why a blade can cut different from test to test and also why it could loose edge and then restore itself. We have different test procedures and yes I agree that with large differences in performance you can draw conclusions about how knives will behave. I think we have to be carefull drawing conclusions on how steels (not knives) will perform based on a couple of tests. I agree Dozier's D2 knives are great perfomers. He does a great heat treat and I would bet that his D2 is close to RC 61/62 based on the results of your testing. I would offer also that his edge geometry, blade finish, and ergonomics also play a major role. From your test on his knife I humbly submitt that you can't say that D2 is always going to have better performance than say CPM S30V or 10V for example. Yes I think that all the factors do influence the result. We do not know the hardness of the AUS8 blade you tested. I would guess about RC 58. If it was pushed up to say 60 and the blade thinned down to .008 inch or so behind the edge then I would bet you would have much different performance. I would agree that Aus8 in general would not perform as good as Dozier's knife in D2. This is mostly cause Bob does not work with AUS8. Anyhow some things to think about. By the way Vassilli where in California do you live? I am about 3 hours from the Bay Area. Maybe we could do a cut a thon sometime..... PHIL
 
I think hardness is not only contributor to performance.

I have several D2 - one on top but one on the bottom, may be I need to retest it, but I doubt it will start performing as an Dozier. And in the middle I have Friction Forged D2 - which with results being not so high amaize me with strange stability - from 15 to 200 cuts not changes being as it was tald by Diamond Knives about 67HRC!

D2 is very interesting steel - it is bulat by composition and I perfectly may see this bulat pattern on Dozier blade side like I have on bulat - like here:

knife73-03.jpg


May be finer and not etched, but I am sure I see it. This suggest that Dozier blade may not only be perfectly heat treated D2, but like bulat has internal carbide structures - not monosteel but some kind of composite. This blade I have does not really perform better then average, but I can imagine that Dozier was able to make it right and reproduce this antique steel.

I would say that I did not really count how hard knife cutting rope, unlike in your method. I just cut it and best so far in terms of comfort was Russian Utes, just because of perfect handle as well as Buck110. I use rope as an load only, measuring impact on very edge, to isolate blade size and thickness ad other factors making same 30 degree edge on all.

Anyway thread is affected only by little fraction of very edge, so until thickness behind (in normal blade range) affect how this fraction get dulled (and I believe it does not) I think I isolate all other factor but edge angle, which I made all same for all blades.

Thanks, Vassili.
 
Thanks for the thoughts, Phil. I agree with you.
Phil Wilson said:
...
In any case an edge at 60 RC will have a strength of about 400,000 psi. The smaller the area the larger the stress so even with a little side load the strength is easily exceeded. What this means is that the sharper the edge the weaker it is. A "hair whittling) edge is not the optimum for cutting rope. A reason why sometimes results are over the map. I applaud Nozh for his work. He must have a very sore hand and wrist. I again have to go back to the premise the this is a test of knives, not steel. Yes you can get some rough ideas on wear resistance between steels but there are so many other variables that it tends to get lost. Hardness equals strength so unless we know the hardness of each blade then its hard to make good comprarisons. Here are some other variables that make a difference:
Blade shape-- A curved blade will cut better and longer than a flat one. The belly concentrates the force on the rope fibers so can cut with force and less wear over the long run.
Length of cut-- A longer slice distributes the force over more edge therefore less wear in any one place.
Hardness-- all ready discussed
Edge shape-- Flat grind is a wedge. A thinner wedge has a better mechanical advantage and less friction (drag). Hollow grind will drag on the flat to hollow transition.
Blade finish-- better finish has less drag.
A push cut-- causes less wear than a slice. So when cutting it is critical to get the same relation between a push and slice each time the rope is cut.

Some of these have more effect cuttting against a scale. But maybe helps to put some of this into perspective..... PHIL
Click to expand...
 
Vasilli, I did some photo micrographs of D2 and CPM S60V by comparison maybe 15 years ago. I remember the large crystal structure you could see in D2 like what you pictured in the Bulat. In D2 what you see are the large chrome carbides. sometimes in strings as long as 40microns. You can also see this structure in 154 CM and 440C, but smaller size carbides. David Boye casts 440C for blade blanks and then acid etches it so the dendrites stand out.You can see huge crystal strings that are really very pretty.
If you believe you are testing the edge holding performance of steel and have removed the "knife" factor then great, you are coming up with some great information and has been the meat of a great thread and discussion.
I have finished several simple knives, all the excact same in grind, edge ect. Steels are: CPM 125V, CPM 10V, CPM 90V, CPM 30V, CPM 154. I plan to do 154 CM, D2 and AEB-L as well. All are, will be, known hardness. Testing so far with my method shows that they fall pretty much in the order I have them listed above. What is interesting so far is that given the optimum heat treat, (at least I think so) that 90V, 30V and CPM 154 are grouping into a similair category. I will post more on this later... Phil
 
Great, I am looking forward to see you results!

I think I isolates everything and I provided all my thoughts why I think so, if you have different thoughts I will like to hear them. It is important, to isolate factors which differs knives from different manufacturers. You probably only one who may do you own knives and you own heat treatment from all this different steels.

But performance of steel in perfect condition does not give you understanding on quality of this or that manufacturer, and not only in terms of bad quality but (what if it is only you who can do it right) mostly in terms of special HT like Dozier and Fehrman and Swamp Rat all have.

So please I really need to isolate it and if you have some doubts which I miss I really like to discuss it.

To you test - I think that unlike I measuring sharpness on thread after cutting rope you doing same with rope itself (this of course require same edge geometry unlike in my case where thread is cut by little fraction of very edge) and I think that like in my case it may require several measurements as well and some statistical average may be median to check.

Also as well it is important to make sure that all blades started from same condition, so I suggest you to measure initial sharpness as well same way as you measure it at the end.

D2 has dendric structures but as I understand bulat has them "managed", by hammering carefully blade down. So this structures not random but somehow works to blade benefit and so I may speculate that Dozier did this too somehow. See more details here:

http://playground.sun.com/~vasya/Bulat-Achim.html#English

Thanks, Vassili.
 
Phil Wilson said:
Vassilli, I was responding to Broos who brought up a point about edge deformation. Didn't mean to leave you out of the discussion. After all it is your thread to start. I was also attempting to explain why a blade can cut different from test to test and also why it could loose edge and then restore itself. We have different test procedures and yes I agree that with large differences in performance you can draw conclusions about how knives will behave. I think we have to be carefull drawing conclusions on how steels (not knives) will perform based on a couple of tests. I agree Dozier's D2 knives are great perfomers. He does a great heat treat and I would bet that his D2 is close to RC 61/62 based on the results of your testing. I would offer also that his edge geometry, blade finish, and ergonomics also play a major role. From your test on his knife I humbly submitt that you can't say that D2 is always going to have better performance than say CPM S30V or 10V for example. Yes I think that all the factors do influence the result. We do not know the hardness of the AUS8 blade you tested. I would guess about RC 58. If it was pushed up to say 60 and the blade thinned down to .008 inch or so behind the edge then I would bet you would have much different performance. I would agree that Aus8 in general would not perform as good as Dozier's knife in D2. This is mostly cause Bob does not work with AUS8. Anyhow some things to think about. By the way Vassilli where in California do you live? I am about 3 hours from the Bay Area. Maybe we could do a cut a thon sometime..... PHIL
Click to expand...

When I have done manila rope cutting comparisons, I have found that I can group the steels into performance groups, but have had difficulty making fine distinctions between alloys. For example, I can see the difference between AUS8 and 154CM, but have difficulty seeing a performance difference between 154CM and VG10. I knew it was not merely a difference in hardness as I measure the hardness of each blade prior to testing. Thank you for explaining.

Phil Wilson said:
I have finished several simple knives, all the excact same in grind, edge ect. Steels are: CPM 125V, CPM 10V, CPM 90V, CPM 30V, CPM 154. I plan to do 154 CM, D2 and AEB-L as well. All are, will be, known hardness. Testing so far with my method shows that they fall pretty much in the order I have them listed above. What is interesting so far is that given the optimum heat treat, (at least I think so) that 90V, 30V and CPM 154 are grouping into a similair category. I will post more on this later... Phil
Click to expand...


Please, please, do.
 
Has anyone done any tests to compare the force to cut manilla rope versus the thickness of the edge bevel?

Has anyone done any testing to confirm that force to push cut a thread versus force to cut the rope are directly (linearly) related?

Those are two differences in the method...
 
Vassilli, My objective in testing is to predict how a knife is going to act in a real world situation.
You mentioned one time the differences in the number of cuts we get. I recall that you cut ½ , but remember I cut 5/8. That would explain the difference.
I don’t sharpen to a very fine edge. I use the knife as it comes off the fine SC Norton or green DMT stone with just a few strokes on a loaded strop to take off the burr. Final edge angle depends on the thickness behind the edge but will be 17 to 25 degrees in most applications. I don’t know what a hair whittling edge is so can’t compare that to what mine is. I was trying to make the point earlier that the sharper an edge is the weaker it is. If an edge is fine enough to whittle hair then for sure it is going to bend, bend back, roll, fracture --or all of those-- with 20-30 pounds force cutting very tough rope. Seems like when cutting the string it is possible that you might be in an area of the edge that is damaged. I was suggesting that for some of the knives you tested that this could explain some of the data you got. In my cutting method I think I am minimizing this effect by a steeper edge angle and the fact that it just shows up as differences in force needed to slice the rope. It all averages out. This is OK or not depending on what your objective is. One thought to consider. How about a thicker string and a longer cutting stroke for the sharpness test?
Another thing that might be interesting is to measure the force needed at the start and after you finish the 200 cuts. This would give an overall feel for the cutting efficiency of the knife. It would probably take about 10 slices for each to see where you are on the scale.
Your suggestion to me, to measure sharpness before I start is a good one. Right now I do this by the scale reading or by the feel of the edge with my thumb. I need to think about how to do this with more precision-- mostly for credibility.
I have to come back again to the premise that we are testing knives. I do not think you accept this. You can draw some conclusions about steel but all of the knife characteristics come into play to tend to wash out the steel conclusions. Hardness for example can make a huge difference. I have found that CPM 10V at 62 and CPM10V at 64 act like two different steels. My cutting work has convinced me that steel comparisons can only be made with identical knives but different steels. I tried to make this point in previous posts here. If you do accept the premise that we are testing knives then testing a folder against a hunter is not a fair comparison for a lot of reasons.
I recently had the opportunity to do some extensive field testing on a Bison hunt. My objective was to correlate the results in the field to my rope testing at home in the shop. In short I found that there is a pretty good correlation. In other words if you can get x number of cuts with y force with a given knife and sharpness then it will do the expected job. I am writing up this experience and hope to get it up on my web site early in 2009. Vassilli, I admire you for your scope of work and the effort involved. I have learned some things and has forced me to think through others. Different people test for different reasons. Keep it up-- and again where are you in Ca. ? send me a PM if you want but would be interesting to get together and collaborate on some of this. PHIL
 
I've done some backyard testing over the years and found that for me even the difference in handle comfort made a pretty large difference in results. I do find all testing very interesting and intertaining. I've just come to beleive that almost all of the so called tests are more subjective than any kind of fact or proof of anything.
 
db said:
I've done some backyard testing over the years and found that for me even the difference in handle comfort made a pretty large difference in results. I do find all testing very interesting and intertaining. I've just come to beleive that almost all of the so called tests are more subjective than any kind of fact or proof of anything.
Click to expand...

I feel your pain - but once I have initially some unsuccessful tests I keep trying and in 4 years came pretty close to what I consider useful. You personal experience should not really be expanded on entire World and everybody, I just keep trying no matter what and came close and close.

For example sharpness measuring really work and allows me to learn how to sharpen, how to polish without rounding edge. As well as even with current presicion I found for myself Dozier as a direct result of this testing and happy to use it - it just hold edge unbelievably!

So of course this need to be thought through, evaluated, but your simple dismissal is just hard to accept - what should we just gave up take as granted whatever marketing drons will feed us with? No I do not think so.

Thanks, Vassili.
 
Phil Wilson said:
Vassilli, My objective in testing is to predict how a knife is going to act in a real world situation.
You mentioned one time the differences in the number of cuts we get. I recall that you cut ½ , but remember I cut 5/8. That would explain the difference.
I don’t sharpen to a very fine edge. I use the knife as it comes off the fine SC Norton or green DMT stone with just a few strokes on a loaded strop to take off the burr. Final edge angle depends on the thickness behind the edge but will be 17 to 25 degrees in most applications. I don’t know what a hair whittling edge is so can’t compare that to what mine is. I was trying to make the point earlier that the sharper an edge is the weaker it is. If an edge is fine enough to whittle hair then for sure it is going to bend, bend back, roll, fracture --or all of those-- with 20-30 pounds force cutting very tough rope. Seems like when cutting the string it is possible that you might be in an area of the edge that is damaged. I was suggesting that for some of the knives you tested that this could explain some of the data you got. In my cutting method I think I am minimizing this effect by a steeper edge angle and the fact that it just shows up as differences in force needed to slice the rope. It all averages out. This is OK or not depending on what your objective is. One thought to consider. How about a thicker string and a longer cutting stroke for the sharpness test?
Another thing that might be interesting is to measure the force needed at the start and after you finish the 200 cuts. This would give an overall feel for the cutting efficiency of the knife. It would probably take about 10 slices for each to see where you are on the scale.
Your suggestion to me, to measure sharpness before I start is a good one. Right now I do this by the scale reading or by the feel of the edge with my thumb. I need to think about how to do this with more precision-- mostly for credibility.
I have to come back again to the premise that we are testing knives. I do not think you accept this. You can draw some conclusions about steel but all of the knife characteristics come into play to tend to wash out the steel conclusions. Hardness for example can make a huge difference. I have found that CPM 10V at 62 and CPM10V at 64 act like two different steels. My cutting work has convinced me that steel comparisons can only be made with identical knives but different steels. I tried to make this point in previous posts here. If you do accept the premise that we are testing knives then testing a folder against a hunter is not a fair comparison for a lot of reasons.
I recently had the opportunity to do some extensive field testing on a Bison hunt. My objective was to correlate the results in the field to my rope testing at home in the shop. In short I found that there is a pretty good correlation. In other words if you can get x number of cuts with y force with a given knife and sharpness then it will do the expected job. I am writing up this experience and hope to get it up on my web site early in 2009. Vassilli, I admire you for your scope of work and the effort involved. I have learned some things and has forced me to think through others. Different people test for different reasons. Keep it up-- and again where are you in Ca. ? send me a PM if you want but would be interesting to get together and collaborate on some of this. PHIL
Click to expand...

My intention is of course not pure steel, but steel from manufacturer. With factory heat treatment. I think I do eliminated in my procedure other factors - geometry etc. And again you objective is how knife will do job, my objective is how long reasonable from my point of view edge will stay. I may assume that thickness in theory may somehow affect edge holding, but I think it is true only on unpractically think edges and for 1/16" shoulf not be different from 1/8" on edge shoulders.

Hair whittling has nothing to do with edge thickness. I usually has 30 degree edge hair whittling. Edge able to whittle hair when angle is close to mathematically ideal being same 30 degree - it is not weaker it is just better.

Here it is (with 30 degree edge):

http://www.youtube.com/watch?v=aQPwHu4lxsQ

And here how I make it:

http://www.youtube.com/watch?v=5TscN9h-1xQ

I'll send you mail. We should meet sometime.

I really like you tests and always very interested in them - they are different but both quite informative and useful - of course with absence of any information all tests are very valuable. You should also look at what Noss4 is doing - he is doing what no one else and I found his effort very interesting.

Thanks, Vassili.
 
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