Some comments on ZDP-189 vs VG10 edge retention

The force you apply is going to be exerted everywhere the blade contacts the material being cut, so the more area, the more force needed because the pressure is reduced everywhere there is contact. It is why thinner blades and more acute angles cut better. And as mentioned, since we are not perfect, the less force we use, the fewer mistakes in the cut, and the lesser the force applied laterally to the edge when we do make mistakes and sideload the edge. Thickness is important at both the spine and at the top of the sharpening grind. The thinner you can go at both, the better your knife cuts. You can reduce the angle to thin out the steel, and you can grind at the same angle to a narrower thickness. The closer we get to a vertical line, or 2 dimensional cutting tool, the less force needed. Deviate from the vertical, and the force splits between vertical and horizontal. So you still need to apply the amount of force to cut, dependent on your edge finish and shape, but now you also need additional force to compensate for the reduction in vertical forces and the increase in resistance on the horizontal axis. Hopefully someone with an engineering or physics background can clarify. To me, this is what is important in all elements of a knife. Ergonomic handle for comfort and control in delivering force to the knife; proper heat treat and alloy to allow for the thinnest stock and lowest grind angles while still maintaining strength & toughness throughout the blade and at the edge to reduce rolling and chipping; and wear resistance so the edge doesn't degrade quickly through wear, causing you to increase force in prolonged cutting even with better overall geometry.


Uploaded with ImageShack.us
 
LX_Emergency said:
So in fact you've just proven the carboard test to be useless in edge retention testing. Since it doesn't test the edge but the thickness of the blade?

Am i getting that right?
Click to expand...

I don't think cardboard cutting is useless, but blade profile as well as the blade steel are variables that impact the performance when cutting cardboard. So the results can be misleading if the blade profiles are different and you don't take that into consideration.

If you compare blades with different profiles and different steels when cutting cardboard, then attribute the entire difference in performance purely to the steel, you may reach an incorrect conclusion.

But cardboard cutting is an excellent method for comparing the slicing performance of two different blades. (Cardboard cutting is the basis of CATRA testing.) You just need to remember that you are comparing the blade steel AND the blade profile, rather than just the alloy.

Hardheart, as usual, has given a much better and more complete answer than I have. Thanks for that.
 
I'm not sure why would one conclude cardboard cutting is useless. For one, it is a cutting work that most of us have to do, often or not.
Second, most of the cutting is affected by blade thickness, unless it's done only on the surface, and cardboard isn't the worse one in that regard. Thick, sticky material cutting is affected by blade thickness and width at far greater extent than with cardboard.
 
How about if you use cardboard for a dulling medium, but don't use the force to cut the cardboard as an indicator for edge retention. A while back, I used cardboard as a dulling medium, and then measured high sharpness edge retention by cutting plastic grocery bags. An edge that will shave hair off my arm will not always split the bag, and the bags are more consistent than body hair. In this case I wouldn't think the geometry of the edge would come into play, at least in the fashion you're talking about above.
 
knarfeng said:
I don't think cardboard cutting is useless, but blade profile as well as the blade steel are variables that impact the performance when cutting cardboard. So the results can be misleading if the blade profiles are different and you don't take that into consideration.

If you compare blades with different profiles and different steels when cutting cardboard, then attribute the entire difference in performance purely to the steel, you may reach an incorrect conclusion.

But cardboard cutting is an excellent method for comparing the slicing performance of two different blades. (Cardboard cutting is the basis of CATRA testing.) You just need to remember that you are comparing the blade steel AND the blade profile, rather than just the alloy.

Hardheart, as usual, has given a much better and more complete answer than I have. Thanks for that.
Click to expand...

I didn't mean that cardboard cutting is useless. Merely that it's useless for an edge retention test. Since after a certain point it seems that the only thing that is relevant is the thickness of the blade, not the type of steel or even how "sharp" the edge is.

Your own experiences seem to point that towards the idea that 2 knives being of different steels but the same grind/edge thickness come out to equal results on cardboard tests.

At least, that is what I understood from the discussion so far.

(not trying to argue, just trying to form some kind of conclusion from the results.)
 
lx emergency what i understand from the tests was a comparison of 2 premium alloys that tried to make = all factors except the very composition of the steels. in any test we try to make everything = except the very fact or composition that varies between the 2 entities.lets not forget the initial cutting was on rope as a contributing variable in the equation.what myself learned from this [i thought comprehensie tests] was that although zdp did out perform vg10 the the human factor that did the cutting could'nt by his personal efforts discern a lot of work difference in actual use of the 2 metals.this tests confirms my experiences cutting cardboard some weeks back. therewas'nt any doubt that zdp was the premium performer however the effort required to preform the tests did'nt require a lot of actual "felt' difference.felt difference is a subjective variable that is'nt easily verfiable since we are taking about the human factor. however when several people doing similar cutting get similar results i believe we can attribute some validty to the experiences. my own conclusion was "value" wise vg10 was was a better bang for the buck. no one was confirming that vg10 was a superior alloy than zdp but bang for the buck vg10 was a greater deal.now many people may critizie the subjective variable as non empirical in the equation;[this being the party doing the cutting]. however i.m.h.o. removing humans from the equation destroys the validity of the whole experience. i ask any member when you cut open a box, cut a steak, whittle wood, or open a large bag of dog food are you going to have a catra machine by your side when you are cutting fishing line at the lake? frank's, my own, & other contributors by thier subjective use feel that the human work factor required to accomplish the same results is not overly substantive when comparing the costs of the 2 metals in relation to the final result. i think you get more for the money spent by using vg10 as opposed to zdp.if i've failed to clear up what was accomplished by frank i'm sorry.
 
LX_Emergency said:
I didn't mean that cardboard cutting is useless. Merely that it's useless for an edge retention test. Since after a certain point it seems that the only thing that is relevant is the thickness of the blade, not the type of steel or even how "sharp" the edge is.

Your own experiences seem to point that towards the idea that 2 knives being of different steels but the same grind/edge thickness come out to equal results on cardboard tests.
At least, that is what I understood from the discussion so far.

(not trying to argue, just trying to form some kind of conclusion from the results.)
Click to expand...

Not quite.
I would restate your comment as, "cardboard cutting does not always properly rank the performance of alloys unless one of the conditions below is true:
1) You are not using the "force needed to cut" as your measured characteristic. (ME2 has a valid point. You could measure other characteristics. But "force needed to cut" is the most common I have seen.)
2) You test knives that have the same profile. (This is an option usually only available to knife makers. I believe Phil Wilson has made knives with identical profiles, but made out of different alloys, and tested them on cardboard.)"

I think there should be a clearer way of stating that, but it's the best I can do at the moment.

 
I think you can use cardboard effectively and not have blade profile and thickness effect your results. It all depends on how you cut it. If you lay cardboard flat and cut it with the knife going no deeper than the edge bevel the blade thickness and grind will never see the cardboard and will have no effect. Just like cutting rope at the end the fibers fall away before the blade grind gets to them.
 
I think you could. But most testers don't cut it that way.
 
Using the observational measurement of wear as knarfeng did in this test, I think having unequal bevel thicknesses is OK in many methodologies, including the one used here. Assumptions made include that the observed wear is contained very close to the edge, and that the sharpness (diameter of the very edges are equal) is equal at the start of the comparison (observable with a good eye and good optics).

More assumptions need to be made to claim equal testing for unequal bevel thicknesses in a force based methodology. Anytime the material being cut contacts the blade, there will be a component of frictional force adding to the cut force. One can either assume that force is neglible, or do more tests to prove it is neglible for the particular method.
 
For my procedure, the cardboard is just a dulling medium. I could just as easily use a box of sand, sheetrock, rope, or anything abrasive/hard enough to wear/fold the edge. The trick is it has to dull the edge fast enough that it doesn't take a month of Sundays to see any change in sharpness, and slowly enough that sharpness doesn't go from 100 to 50 in 3 passes. Also, cardboard is fairly common, though for a good blade, it's hard to get enough together to really dull the edge. That's why I tried Al cans, though they don't seem to dull the edge much faster.
 
me2 i ditto that. cutting certainly needs some time expended to be a realistic test. afterall trying to see how long an edge endures gives us a therometer as to edge abrasion in actual usage. as you mention a cutting medium that dulls an edge in one minute is hardly a realistic gauge of real life usage of an alloy. thanks for that perspective.
 
It all depends on perspective I guess. For knives, cutting dirt will dull any steel so fast that getting any meaningful measurements is nearly impossible. I read a machining article once that the writer was tickled ****less about doubling his tool bit life. It went from 30 minutes to 60.
 
Thanks for the info Frank!

I've only had limited experience with VG10...only a few knives vs dozens in 1095... and none at all with the ZDP. I recently got a Fallkniven A-1 that is laminated VG10 and I was concerned about the higher RC (higher than I am used to) with it being 59. But from what I am understanding of the metals, even though it is likely 58-60, that isn't high enough to be too brittle for that particular steel with it being laminated? I know it's sure holding an edge very well as after several minutes of chopping through some very hard seasoned Dogwood and then whittling in the same wood it still shaves nearly as easily as it did to begin with.
 
Interesting discussion. I enjoyed reading all the discussion. I have enjoyed and will continue using sharp knives of various blade steels and geometries...:)
 
You must log in or register to reply here.
Back
Top