Some carpet cutting with a couple of 52100 knives

[Cliff Stamp]

The first intended goal was to measure the extent of blunting by looking at sharpness during the cutting. The Pronghorn was compared to a 52100 MEUK. Both knives were polished to a fine shaving edge with a 22 degree microbevel. Both tested very well on slicing 1/4" poly under a 1000 g load, cutting the cord in under a cm.

However after just two slices throught the carpet, of two inches in length, both blades were pretty much totally blunted. They could not cut the poly in the contact region, just scored it. The edges of both blades fully reflected light as well. With that method pretty much bunked I decided to just see how much carpet could be cut, and could the blades be separated by feel.

After 161 cuts, with pretty much no change in the cutting performance, I stopped cutting as I wanted to preserve some carpet for future trials. The blades could not be differentiated by feel, and both could still cleanly slice the carpet. Though they were requiring more pressure to do so (measuring this would be worthwhile).

The edges were examined under magnification and the reason for the performance not degrading was immediately obvious. There were huge gashes in the edge, and in fact scratches along the primary grinds of both knives. The grit in the carpet had in fact acted like a coarse abrasive and made a micro-serrated edge. The level of abrasion was very rough, far past find DMT.

The blades were steeled, which had no effect on the slicing ability. A fine ceramic rod was used (again at 22 degrees), for multiple cycles of 10 passes per side. This had no effect either, the wear was too extensive. The blades were still unable to cut the 1/4" poly even under almost 5 lbs of force, both were still very blunt. Some rolling was present under mag, but blunting was mainly induced by wear.

A 1000 grit AO waterstone (one inch wide) was used in small circular motions (because I am more accurate that way) to sharpen the blades, using 100 circles per side. The progress of both blades was watched evenly during the honing. Neither seemed to have an advantage. A 4000 grit waterstone was used for two more sessions of 100 rotations each and both blades were now free of any reflecting areas and very sharp.

So in summary :

1) both blades even though having very thin edges, with high relief angles, were able to resist any significant damage even when cutting very hard material, abrasive enough to actually cut into the steel

2) it doesn't seem to be practical to cut until the blades can't cut any more as they actually self-sharpen past a certain point and thus don't get any duller unless you wore away so much material the edges thickened (removed the edge bevel)

3) both blades were worn enough through the cutting to require use of a benchstone to sharpen, steeling or the use of a v-rod was not practical, however the honing was only a few minutes per blade

4) neither showed a significant advantage in regards to edge holding, durability, or ease of sharpening.

5) used carpet can dull even a quality blade very fast, and thus little cutting has to be done to guage edge retention. Beyond even a small sample edge retention would have to be guaged by honing time which would then include the ease of machining.

The next thing I am going to try is to include a few other blades as a benchmark, some harder more wear resistance ones, and some softer less wear resistant ones and see how they fare. I am also going to try to do less cutting, and see if a more precise estimate of honing requirement can be determined as was done with the blades from Ray Kirk.

-Cliff

 

[db]

Any difference in hand comfort?

 

[Jeff Clark]

Carpet dirt is a severe abrasive. Maybe new carpet would slow the wear process down and make it more easily measured. I wonder whether new or old carpet is more representative of accelerated "normal" wear. You could probably get scraps of carpet from a carpet store, a carpet installer, or around a new housing construction project.

 

[Buzzbait]

Old carpet is one of the nastiest things to cut that I've come across. I was cutting some ancient carpet around the family camp last year, and totally blunted the edge of my Dozier K-4 in just a few cuts. I was surprised to say the least. It turned out that the carpet was filled with sand and small rocks and such. Nasty stuff!!!

One question though. Cliff, you mentioned that both knives were sharpened to a 22 degree bevel. Doesn't the Pronghorn have a convex edge? It sounds like the Pronghorn might have performed better if the convex edge had been left intact.

 

[Cliff Stamp]

Db, ergonomics are very different for those two knives. The Pronghorn is very grip specific due to its extensive contouring, it doesn't fit my hand well except in a couple of grips. My hand is however fairly large and thick. The MEUK is much more versatile. This is one of the big problems with ergonomics, but carries over to all areas of performance, focus vs range.

Jeff, yes, new carpet would be slower to blunt, and also a lot more uniform. It would be worth looking at as well.

Buzzbait, the primary grind is full convex, however there is a secondary flat edge bevel. Leaving it at full convex would likely make it very prone to damage considering how acute this would leave the edge (<10 degrees per side). Of course increasing the final edge curvature would reduce the impaction damage, the same would hold for the MEUK.

-Cliff

 

[brownshoe]

Why put a polished edge on a blade that will be used to cut carpet? Basically that's an oxymoron. You should put on a coarse strong edge of a stlye (e.g. angle, back bevel, etc.) appropriate for the type of cutting/material that the test requires and the edge design. In addition, most knife makers, even factory knives, will tell you what type of edge is most appropriate for their blades. Just ask.

 

[Cliff Stamp]

brownshoe :

Why put a polished edge on a blade that will be used to cut carpet?

Mainly as that was the initial state of both knives due to some other cutting which was done just previously. The run mentioned in the above was done mainly as a trial to examine method, so the goals were fairly general in nature. However as with all tests done in the reviews, performance is examined under various grit finishes, specifically including ones which are not optimal.

However, based on the rapid rate and type of blunting, I don't think that a more coarse edge would offer a significant gain in lifetime, and may even result in more rapid edge loss due to possible fracture of the microteeth, which would then lead to faster edge thickening.

In addition, due to the nature of the carpet, the cut is also very strongly push dependent, very little will be cut on a low push slice. Most zipper cuts done on such materials are optimal with high polishes for this reason. These blades are slim enough to do this well, other much more heavily profiled blades would have to resort to a sawing motion.

When slicing ropes, the micro-teeth (even when very deep at fine angles) are easily strong enough to resist gross damage. However here, like chopping wood, they may simply break either through direct impact failure or by passing ductility limits. In such cases the edge holding can be poor, and the loss of metal much greater than with higher polishes.

Back to the work :

I prepared the CPM-10V for the cutting last night so it is good to go now as are the MUEK and Pronghorn, all with 600 DMT edges. I am still trying to clean up the Opinel.

Awhile ago, in an effort to remove the secondary edge bevel, a very coarse abrasive was used (40 grit ZO) which turned out to be not a very good idea as it left very deep scratches in the primary grind which are opening up to visible serrations in the edge.

These notches are just under a mm or so deep, and this would likely give the Opinel a large advantage on any kind of sawing cutting as it is in effect a serrated edge. I might try it with this just to note the level of effect and compare it to the edge after further work to refine it.

-Cliff

 

[Buzzbait]

I agree with Cliff about the grits. Using a very coarse grit edge on that carpet may have ripped the edges all to hell and back, even if the initial performance may have been accelerated. You have to ride that fine line when cutting nasty materials, between performance and durability.

 

[brownshoe]

Shouldn't you use the type of edge that the maker recommends? Cliff, have you found out the maker's instructions for sharpening?

Take Spyderco for example, since they sell a sharpening system with specific instructions for their knives. Their video indicates that they recommend sharpening at 40 degrees stopping with the flats of the coarse stones. They state this gives the best utility edge. Wouldn't a 40 degree somewhat coarse edge be the best way to sharpen a Spyderco for testing in carpet cutting?

I've bought 6 handmade or custom knives, each maker has indicated the purpose of the blade and how they believe the knife should be sharpened. I have two chisel ground blades, both with widely different instructions for sharpening. Sharpening and testing should be in accordance with the blade design.

 

[Cliff Stamp]

brownshoe :

Shouldn't you use the type of edge that the maker recommends?

If you wanted to do a purely promotional review for the maker of course you would let them decide exactly how the work should be done. I would agree that work should be done to showcase the makers intended goals, but would not restrict the work to just that for rather obvious reasons which were pointed out in the recent Pronghorn thread. Doing so would completely remove the ability to point out weak points in the designs, and leave you totally unable to compare the knife to blades made by other makers and prohibit exploration of individual aspects (geometry or steel) which could be useful in other knives.

Cliff, have you found out the maker's instructions for sharpening?

Ed goes into this in detail on his video which I bought some time ago.

Take Spyderco for example, since they sell a sharpening system with specific instructions for their knives. Their video indicates that they recommend sharpening at 40 degrees stopping with the flats of the coarse stones. They state this gives the best utility edge. Wouldn't a 40 degree somewhat coarse edge be the best way to sharpen a Spyderco for testing in carpet cutting?

It would not give the best performance if that is what you are asking. The Sharpmaker in general doesn't give optimal edges for a lot of cutting tasks. Most utility work could be done with far more acute, and often far more coarse edges. I also don't agree with Sal on sharpening 100% either, such as his comments that the purpose of a strop is to create a burr or fine wire edge. This is a common misconception which leads to the myth that polished edges are frail.

Sharpening and testing should be in accordance with the blade design.Sharpening and testing should be in accordance with the blade design.

This ignores the fact that opinions on such issues are not universal. You can have makers with near identical knives and radically different opinions on how to sharpen and scope of work. Thus comparing the two knives would obvious lead to cross overs, extending this to commenting on a knife in general has a very obvious conclusion.

It also ignores the fact that performance could be enhanced by different sharpening methods, and that the scope of work could be more narrow or more broad than they thought. I have used custom knives for many tasks which the maker never assumed their knife would function, mainly as they had never tried it.

In regards to sharpening, a rather obvious point would be that people may be interested in how the knife would perform with other grits and methods of sharpening as it is what they are familar with. Some work well, some do not. The weak points as well as the strong points of knives are commented on.

In regards to specific grits, compare to the NIB finish, the performance of the Pronghorn can be enhanced for most push cutting with the use of a more polished finish, and slicing can benefit from a still more coarse finish, both aspects will be noted in the review commenting on raw cutting ability, edge life times and rate of blade wear.


Of course at any time during the review (or even after) a maker is free to suggest changes in sharpening, or method in general.

Back to the carpet :

This weekend I finally got around to doing more cutting. Four knives were used of various steels and hardness levels. The cutting was not nearly as extensive, only 14 cuts were made in total with each knife. The cuts were done in random order to reduce systematic effects from possible very dirty patches.

The extent of blunting could be noted among the blades with a clear difference in how much sharpness was lost in regards to ability to cut various cords (push and slice). The edge behaviour was also clearly distinct in the extent of reflection of light, and the amount of damage which could be noted under magnification. The blades also responded at various rates to steeling and honing. This needs to be repeated a few times to allow prediction of decently robust behavior.

For this run a 600 grit DMT rod was used as the final finish, not as much for the performance increase, but mainly as it was a much more aggressive sharpener and thus could be used to judge the extent of blunting at the edge by sharpening (this is then influenced by machinability as well). In regards to raw performance, the micro-serrations by the DMT finish are wiped off pretty fast and within a very short period of time the cutting action is dominated by the edge finish as produced by the grit in the carpet as noted in the above.

Based on the cutting and the extent of damage induced (100-200 microns), even a very coarse finish (100 grit AO) is not likely to eave teeth large enough to induce a saw effect for any length of time (they are smaller than the chips knocked out of the edges). Such large teeth would also be more prone to damage than a finer finish and would also induce a greater extent of metal wear. However there could be a self-sharpening effect depending on the nature of the breakdown of the steel. This would be something to look at. Push cutting the carpet would also be optimal with fine polishes so this would be informative to do as well.

-Cliff

 

[brownshoe]

Cliff your arrogance is astounding. You basically stated that Sal Glesser and Spydercos 25 years of experience in both materials and sharpening systems is nothing compared to your large brain.

It makes no difference to you that a maker designs a knife for a particular job and has a recommended method of sharpening. Following the design is like following the directions. It should be the first point in testing. If a knife makers design/edge combo is poor, you can stop testing. Any further work done with different types of edges is experimental on your part, not really a test of the knife as designed by the maker.

Your lack of respect to the professionals of this business is astounding. So is some people's belief that your discovery that thin hard blades cut better is revelatory and science. You'll probably discover the wheel tomorrow.

 

[Buzzbait]

Give it up brownshoe. As often as I may disagree philosophically with Cliff, he's right on in this thread. Cliff may not be 100% right in every word he says, depending on your point of view, but his premises are correct for the type of testing that he’s doing. You’re looking that start a fight with Cliff in the wrong thread. Give it up.

As far as the Sal Glesser comment goes, there are different styles of sharpening. I would not call anybody right or wrong when discussing sharpening techniques, unless there was a grievous error. Sal could be right using his technique, but Cliff also uses a very sound sharpening method.

 

[Cliff Stamp]

brownshoe :

You basically stated that Sal Glesser and Spydercos 25 years of experience in both materials and sharpening systems is nothing compared to your large brain.

No I basically stated that I don't agree with him 100%. What you stated, while colorful, doesn't follow. Now if I said that I agreed with him 0%, and he was a ignorant nob, then you would have a point of merit.

It makes no difference to you that a maker designs a knife for a particular job and has a recommended method of sharpening.

Which I never said, in fact I did say that makers were free to suggest work done to be included which would illustrate the focus of their design.

Following the design is like following the directions. It should be the first point in testing.

Yes, why I said such work will be included in the review.

If a knife makers design/edge combo is poor, you can stop testing.Any further work done with different types of edges is experimental on your part, not really a test of the knife as designed by the maker.

Exactly, and since the work I do is not primarly designed for that purpose your arguement does not apply. Your line of reasoning also ignores that this maker "opinion" is not uniform, and thus following your advice prohibits reviews in a relative sense and keeps them isolated and thus meaningless. It is also what propogates many of the myths in the industry.

Your lack of respect to the professionals of this business is astounding.

Which is implied by the fact that I don't agree with every maker says? Which by the way would be impossible as they constantly contradict each other. That point itself illustrates a fairly major problem with your central arguement.

So is some people's belief that your discovery that thin hard blades cut better is revelatory and science.

As noted, I have given credit for the fundamental ideas of hardness on edge retention, and grit influence and edge geometry (especially thinness) on cutting ability to Alvin Johnson and Mike Swaim, work which was later extended significantly by Joe Talmadge.

Lots of others have done similar work, Goddard for example noted the effect of hardness on edge retention, his work was extended by Wilson who found wear resistance a much more secondary effect. Busse brought in the effect of impact toughness and ductility on edge retention on heavy chopping knives.

Leonard Lee talks about all three effects in his book on sharpening in some detail as well.

You'll probably discover the wheel tomorrow.

Man are you behind, I discovered the wheel just after I invented the internet, and before I patented sliced bread. It was just about the same time I discovered iron and came up with fat free potato chips (and new coke).

Buzzbait :

As far as the Sal Glesser comment goes, there are different styles of sharpening. I would not call anybody right or wrong when discussing sharpening techniques...

You have to look at what he was trying to do. Consider a Spyderco blade with an applied high relief convex grind to the shoulder, and stopping the polish at a lower grit. Is this modification right or wrong. It is a meaningless question as it isn't defined. .

The Sharpmaker is simple to set up in a few sentances, requires ittle skill to use, and almost no maintaince. Can performance be increased by deviating from this setup, of course. However then you get into angle particulars, relief grinds and grits. For someone getting into sharpening this just presents too much confusion as the edge angle (for a particular task) depends on the steel, heat treatment and skill and strength of the user.

It is just like the maker comments that brownshoe made. Does anyone actually believe that everyone should have the same edge angle and finish on their knives. Of course not. Even the makers who recommend the same thing don't agree with this, like the Sharpmaker solution, they will give a general responce, which the user can refine for greater performance. There is evidence of the kind of improvement that this can make in the reviews, Joe Talmadge has done this as well, showing improvement of ~700% with an alteration of geometry and grit level over the maker / manufacturer edges.

The recommendations on sharpening are just a starting point, the edge profile and sharpening method should be refined to suit the users scope of work, skill and physical ability. There is no maker I have yet seen that would argue this isn't reality and that everyone would have optimal performance with their stock edges.

-Cliff

 

[Roadrunner]

I always love seeing your responses to criticism Cliff. The hardest thing for most people to do in response to criticism is keep their cool, and it's also the most confusing and infuriating response for an antagonizer. Very nice review as well, I had never really considered how abrasive old carpet would be. If I can find some I may use it to test the Spyderco Lil' Temperance that I have as part of a pass-around right now; I could compare it to my Kershaws in 440V to see if the different heat treats affect performance.

 

[brownshoe]

Thanks for the advice Buzzbait. I will give it up; on this and other cliff threads. However, I find it hard to see it wrong to test a knife with the designer's edge grind and in ways for which the knife was originally designed. This is the legitimate first test, the one by which the knife should be first judged. Other tests are extensions to the original purpose of the blade. Same example, why skin a hog with a Swat entry tool? Just becaust it can be done?

 

[Gabe Newell]

Standardized tests are a very good thing.

If you are testing a CPU, you test its floating point performance regardless of whether or not it is going to be a home machine used primarily for email or an engineering workstation used for doing atmospheric simulations.

A test is more useful if you have lots of other instances where you've run that test.

In some cases doing poorly or failing at a given test is perfectly reasonable, expected and desirable if, for example, the intended use would benefit from a trade-off between the characteristic being measured and some other characteristic.

In other words, you would expect and desire a small pocket knife to fail edge impact tests, but you would still be curious at what point it failed and whether or not the expected corresponding increase in abrasion resistance materialized.

What you want to avoid are idiosyncratic or one-off tests that make it impossible to compare the results with other testing.

So why skin a hog with a SWAT entry tool? Because you tested all of the other knives by skinning a hog.

 

[Gabe Newell]

"Intended use" is the filter which you apply to the results of standard tests, not the criteria used to create non-standard tests.

 

[Roadrunner]

brownshoe, please don't give up posting in any subject you feel the desire to add input to. I have no issue with your last post, you respectfully disagreed with Mr. Stamp and offered reasons for doing so. That's what debate is. My issue is when you make personal attacks and resort to name-calling and insults. That degenerates the conversation and doesn't help anything, least of all the views you are defending. That stuff belongs in W&C, not in a serious discussion. Don't withdraw your input, just make it constructive and relevant.

 

[Copis]

I use a coarse edge when I want "bite", but I find it less durable than a polished edge

To basically push-cut thru old or new carpet I use a polished edge. I find it optimum for push-cuts in terms of durability.

It has nothing to do with makers recomendations and suggestions. It has everything to do with the way you use your blades

Are you going to tell me that I use my blades wrong? Knives are a personal and individual thing.

BTW I'm told on a daily basis that my arrogance is astounding!

Bill

 

[Cliff Stamp]

brownshoe :

However, I find it hard to see it wrong to test a knife with the designer's edge grind and in ways for which the knife was originally designed.

You say this like someone is opposing it. What I and others have argued is that work done with a knife can be extended beyond the intended scope of work to allow information to be gathered for other purposes. Such information isn't used to judge the suitability of the knife for its intended purpose.

Well to complicate matters somewhat it can be in certain cases due to differences in opinion mainly on techniques and to address tradeoffs in design. For example lets say you have two utility knives and one of them was designed not to cut bone and other hard materials.

In a review of such knives, I would first do the work in the intended scope of work of the weaker knife. Later I would work to illustrate the drawbacks compared to the other knife. What is being shown here is the tradeoff of cutting ability for durability and specifically range of functionality.

This isn't used to judge the maker of the knife, but comment on the usefullness of the knife in a general manner. For example the Deerhunter will in general out cut the Howling Rat on thick and binding materials. The Howling Rat is better at twisting, prying, splitting and other heavier work.

Similar methods can be used for other performance ablities as makers will in general have vastly different opinions on scope of work issues even if promoting knives for exactly the same thing general purposes (survival, hunting, combat etc.) . When such knives are being directly compared, which is frequent, the most broad range of work is done, otherwise the testing would be biased in favor of the more focused knife.

Roadrunner :

I had never really considered how abrasive old carpet would be.

Fibreglass insulation is very abrasive as well and is also readily available in consistent bulk form. I considered that but it really irritates my skin. If you can stand contact with it (it doesn't bother some people), it makes a very nice extreme testing medium.

gaben :

"Intended use" is the filter which you apply to the results of standard tests, not the criteria used to create non-standard tests.

Yes, and point made very precisely. Look at the conclusions drawn from the tests. This is how their merit must be drawn. This is basic logic. You can judge a test irrespective of what it is being used to determine.

Copis :

Are you going to tell me that I use my blades wrong?

Yes, unless you can find a maker to tell you otherwise, don't ask too many though because if they give you different opinions you are screwed. I have been on the phone the whole morning trying to get in contact with Skippy as I need to know which is the right way to scoop peanut butter from the jar, clockwise or counterclockwise? Does anyone out there make peanut butter?!

-Cliff