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Marko Tsourkan
09-09-2011, 02:32 PM
As I mentioned in one of the posts, I would like to start comparing edge retention among knives from different makers, Japanese and American.

I asked a member here to help run the test and have a volunteer who will bring his KD for testing.

I think this time, we are going to compare knives in AEB-L, 52100 and a tool steel to KD, all with DT heat treatment. R2 was mentioned as one of the high performing steels, so it would be fun to test it as well if somebody cares to volunteer their knife.

How the test would be run.

All knives will be sharpened to about 3K and will have about the same level of sharpness (to be determined how to measure it, please advise) by same person so we have a consistency in edge.

The cutting will be done on a block of a hardwood that sits on top of a digital scale. Only 2-3" of the edge will be exposed (the rest taped off) to expedite the dulling. We will be cutting 1/2" sisal rope and recording a number of cuts.

There is certain amount of pressure applied during a slicing cut and a scale reflects that. On my last test, the pressure varied between 18-22LB on a fresh edge, and I attribute the rather a wide range to a lack of a cutting technique. I think we will address that by having a person do the cutting who works in a pro kitchen. :)

Once a pressure during the cuts starts exceeding an acceptable range, it means the edge is dull. We then compare the number of cuts among different steels, makers, etc.

It it important to match geometry of the knives, as a thinner knife will do more cuts than a thicker one, but even without comparing knives one to another, one should have a pretty good idea about edge's holding ability.

Bill Burke does a lot of similar testing for his knives, so I will email him for some advise.

I will also contact a few others guys who are local to come and partake in the test. It should be fun.

M

Larrin
09-09-2011, 02:46 PM
Are you sure that slicing rope is the best test for kitchen knives? After all many members of the forum claim to do primarily chopping/push cutting. I'm not sure that rope is the best medium to simulate food, either. Furthermore, slicing rope, at least outside of Ed Fowler, is controlled primarily by wear resistance, which I still do not believe is the dominating property required for edge retention in kitchen knives. However, this view is primarily promoted by Roman Landes, and I'm still open to suggestion. But my opinion, at least, would not be changed either way by more rope cutting tests.

Marko Tsourkan
09-09-2011, 02:53 PM
Cutting rope with a push-cutting technique is much harder than slicing but we might try that as well. I am also open to other media to be used, but for now, I can't think of anything else. Bill Burke uses a similar test to assess performance of his knives and quite successfully I would say, so this could be a good start.

Results of a rope-cutting test can be interpreted to reflect a number of things: steel, geometry, heat treatment, etc and by no means will it be a scientific test, but it will give us some food for thought.

This is all new to me, so I am very much open for suggestions.

M

Larrin
09-09-2011, 03:20 PM
I also think you're in for a long road to get any of these tests to work. Movement on the scale is sporadic and difficult to quantify. It would take significant experience to do it that way. This would mean you need a repeatable sharpness test, which then means you'd have to develop and practice that test as well. Furthermore, the sharpening consistency is incredibly important in these tests. I'm not anti-testing, to be sure, but remember not to be too optimistic.

Marko Tsourkan
09-09-2011, 03:21 PM
Maybe it is where Edge Pro can come handy? :)

What would make a good sharpness test? I was cutting paper to assess edge sharpness during the the last test. Is there a better way? I don't want to go past 3K edge for a rope-cutting.

M

Eamon Burke
09-09-2011, 03:31 PM
A common logical misconception(as understandable as it is) is that kitchen knives get dulled by the food you are cutting. While this may be true for, say, carbon steel blades cutting sundried tomatoes, or leeks(with little rocks), or knives that never touch the board(like yanagiba), it is not the case for 90% of kitchen work. Cutting 500 potatoes in half by holding them in the air and push cutting them into the garbage will not nearly cause the degredation that cutting the same 500 in half into a cutting board will. Most all knifework is done on a board, and the board's part in the situation cannot be understated.

I would consider the best, most applicable edge retention test to be banging a knife into boards of various materials(or striking board materials into the edge, either way is the same result), with mechanically controlled force, and analyzing the edge with a powerful microscope.

Also, I think this is a situation where the Edge Pro would be greatly suited for the task. Imagine that.

Keith Neal
09-09-2011, 03:32 PM
Marko:

This sounds very interesting, and I look forward to your report.

I'm sure you know this, but I'll wade in anyway just in case I can help.

In any experiment, control of the variables and repeatability of the results are key. That is going to be difficult in this situation, but perhaps there are things that can be done to help.

Perhaps you could arrange some sort of mechanical device to perform the cutting with the same force and movement each time. Rather than try to record the force required to fully cut, measure the number of full cuts made with the same force before the edge fails to complete the cut. That would give you a finite number to compare.

Perhaps some measurement of the "same level of sharpness" could be invented. Microscopic examination or something. I don't have any brilliant ideas for that one.

It would really help if you could find knives of the same type -- all gyutos for instance.

In any case, reducing the uncontrolled variables will give you and us more confidence in the test results.

Good luck. It should be very interesting.

Keith

Marko Tsourkan
09-09-2011, 03:38 PM
I don't have means or ability to build a mechanical device, so we will have to rely on our skills and try to account for variables the best we can. Edge Pro might be considered for consistency of sharpening.

I repeat, but no means it would be a scientific test, but I am confident some conclusions can be drawn from it.

M

Larrin
09-09-2011, 03:40 PM
Johndoughy has an interesting idea. Probably the best way to do it would be to drop the wood onto the knife from a controlled height (to prevent changes between knife weight). Different hardnesses of wood could be used as well as different heights. This leads us to the recurring problem of different edge geometry, however. "Similar" geometry isn't good enough. If both rope slicing and cutting board chopping tests were done a more complete picture of edge retention could be found.

As for sharpness testing, microscrope analysis would be interesting. With slicing sharpness testing, you can attempt to measure the length of the edge required to slice a predetermined object with low abrasiveness and high consistency. Push cutting edge retention is somewhat more difficult. A consistent artificial material thread under consistent tension with a small scale could do the trick. It's been done before, at least.

Eamon Burke
09-09-2011, 03:40 PM
I don't have means or ability to build a mechanical device

I understand, the test I think would be definitive would require a mythbusters-type budget. But I still think the focus should be off the food and on the board.

Marko Tsourkan
09-09-2011, 03:47 PM
The board will be a piece of hardwood, likely face or edge grain walnut (not end-grain) and same board will be used consistently. A choice of cutting surface and a choice of rope as medium is to speed up the dulling of the edge, as some edges can last a month+ in a pro kitchen, so we would want to shrink it down to a manageable time. The last time I did the test, it took me about two hours of cutting (mind you, I am not a good cutter, plus I had to keep track of a count) before the edge was dulled, so if you test more than one knife, this can be a time-consuming event.

M

Marko Tsourkan
09-09-2011, 03:54 PM
Johndoughy has an interesting idea. Probably the best way to do it would be to drop the wood onto the knife from a controlled height (to prevent changes between knife weight). Different hardnesses of wood could be used as well as different heights. This leads us to the recurring problem of different edge geometry, however. "Similar" geometry isn't good enough. If both rope slicing and cutting board chopping tests were done a more complete picture of edge retention could be found.



A device like this I can build. I already have a design in mind. :)



... A consistent artificial material thread under consistent tension with a small scale could do the trick. It's been done before, at least.


Do you have a reference to this?

M

Larrin
09-09-2011, 04:19 PM
You can reduce the cutting time on rope with higher grit sharpening. The chopping test might also be easier to compare with higher grit sharpening. I'm trying to find a good reference for you on the sharpness test.

Dave Martell
09-09-2011, 04:31 PM
A consistent artificial material thread under consistent tension with a small scale could do the trick. It's been done before, at least.


Oh no Larrin.....you're not going to say that name are you? :slaphead:

Larrin
09-09-2011, 05:02 PM
Oh no Larrin.....you're not going to say that name are you? :slaphead:
He's not the only one. There's also the CATRA sharpness tester but the cost would likely be prohibitive: http://catra.org//pages/products/kniveslevel1/st.htm

Marko Tsourkan
09-09-2011, 05:16 PM
Thanks, Larrin -