Edge Retention Test Stand

[grepper]

When I think of making an edge retention tester many questions come to mind, and when I think about each one it leads to more questions.  At first it seems like a simple idea, but after even a little consideration I think there is a lot more to it.
 
For instance, consider an edge retention test for kitchen knives.  In that case, the material being cut, broccoli or whatever, is not going to dull the blade much by itself.  What dulls the blade is contact with a cutting board.  That contact with the cutting board is mostly in two forms, straight or slightly angled impact from chopping, and slicing across the board surface.
 
Just touching on the many implications of this, one obvious question is, would the test cylinder be made of wood?
 
Consider this sentence from Mike's description of the idea, “The new test stand will be capable of gradually indexing a sharpened edge across the length of a long cylinder as the cylinder is rotated.”
 
Now, I’ve never layered spinach over the edge of a blade and then run a rolling pin over the blade to slice the spinach.  Would it be better if the test cylinder did not rotate and was just dragged over the blade?  Would that yield different results than if the test cylinder was rolled over the blade?

I'm not trying to resolve this particular question here, but rather pose these questions as an example of the complexity of the issues.
 
I’m glad that Mike is considering this a collective effort of the Exchange members.  To me it seems much more complicated than first meets the eye.  Many minds providing feedback and ideas on this will no doubt yield a better result in the end.  I suspect it will be an evolving project.

[Soxx]

I'll leave it up to you guys to decide how this machine should be designed but it seems to me that we should talk about what we are testing for before deciding how the machine should be designed. I can see that Edge is building in a fair amount of flexibility into the current design and that may work out just fine but Mr. Grepper raises a fair point. It may turn out that Edge's design proposal is just what we need but let's get some conversation going here with regard to what we want to find out. So I'll start the ball rolling here because this is all very interesting to me on several levels.
 
First of all, what group of knife users is going to have priority here? Is it going to be the bunch who carry high hardness steel folding knives around in their pocket or the ones who use stainless steel cutlery in their kitchen every day? I can pretty much assure you as to which is the larger group. Perhaps it is neither, maybe something in between. Second, what aspect of dulling are we testing for (degradation as Edge puts it.)? Metal wearing away, edges rolling, edges chipping, edges flattening out? I have an opinion on that but I'll finish my list here first. How about factoring in how difficult or easy it is to put a new edge on a knife after it has been dulled. I think that a ceramic knife would fair pretty well in edge retention tests, maybe even King, but once it becomes dull or damaged how difficult is it to put a new edge on? So I'll stop asking questions and, like I said, start the ball rolling with my opinion on at least one of these questions.
 
I don't see the sense in conducting tests that we know the answers to. Harder steel is going to be tougher to grind down than softer steel. Steel manufacturers provide huge amounts of documentation already on these steels. I suspect that harder steel edges are more difficult to roll but don't know that for certain. I do know that every knife I own is subject to rolling though and I would go so far as to say that is the prime reason my knives edges get dull. I've run test after test with a leather strop block or a sharp pad and one of my edge testers. Same story nearly every time. Rolled edge and not missing metal. You can only straighten an edge so many times though and then it needs to be sharpened. So there is my two-cents on that.
 
If we are talking about rolled edges I would be very interested in seeing what factors contribute most to the rolling of edges. Sharpening angle, grind, blade geometry, initial edge sharpness. Here's a question for you. Would an edge that rolls fairly easily but can be straightened easily be better or worse than a knife edge that resists rolling but can't be straightened? I've got a friend  who used to own 5 meat processing facilities in California who wouldn't spend three seconds thinking about that question. I'll give you a hint, he's a grand master with his sixty year old butchers steel.
 
Thanks to Edge for putting this forum together. I watched it for a week before signing up. I've seen mostly respectful conversation here and an appreciation for everyone's viewpoint. If it stays that way, and here's the bad news for you guys,  I plan on being here a long time.  

[grepper]

I agree.  Not only should we ask what group of knives/users are we testing for, but also what questions is the edge tester attempting to resolve.  It is difficult to seek answers to unasked or poorly defined questions.
 
When I first heard of the tester, my initial reaction was that it would just affirm the obvious.  As Mr. Soxx stated, hard steel is going to perform better than soft steel.  So why bother?
 
I think one example of a possible answer to that question is that the tester may be able to help answer questions like what the most effective blade hardness, geometry and level of sharpness is for a particular blade in a particular environment.  For instance, is paying more for a harder steel blade more cost effective than just replacing it more often?  How does that relate to sharpening costs or equipment downtime?
 
I’ve read that many chefs prefer more ductile, softer steel blades because they are easy to sharpen, take a nice sharp edge and are easy to quickly maintain with just a few masterful swipes on a steel.  On the other end of the spectrum is the probably millions of knife steels that sit unused because people don’t understand their purpose.
 
So I agree.  At this point there are far more questions than answers, not only in design and implementation, but also more basic, preliminary questions such as why and what for.

[wadebevan]

Wanted to throw my .02 in.
My primary goal for knives is kitchen use. Not commercial kitchen use, but just home use.
Being an amateur chef and a little obsessed about it, I use my knives a lot, which is what led me to make my own knives in the first place.

After using my first knife (the Nikiri) in the kitchen for about a week now, I know based on experience/feel that the high carbon tool steel is far better at edge retention.

But, it is subjective. I would like to learn more about a more scientific/objective way to 'dull a blade under controlled circumstances'.

I've read a few things about cutting cardboard or paper or whatever on the internet, but, these too seemed pretty 'slushy' in the details.

[wadebevan]

Hey all, I am revisiting this thread because I should have my new Edge on Up PT50A tomorrow, and I wanna get testing!
My plan, as unscientific as it may be, is to sharpen, measure, cut, measure, cut, measure... and so on.
The cutting is the part that isn't very accurate, so I plan on at least trying to replicate the details for each cutting session.

I know the cutting board is likely to do the most dulling, so I will try to keep my cutting style the same at various parts along the edge, and with the same board.

I also plan on having a control blade for reference, in this case I will use a Shun-Ken Onion sharpened to the same initial sharpness.
(My Nikiri has about the same edge angle of 16*)

Any suggestions on what material I should cut in between measurements?

[Mark Reich]

I'm  late to this party, but I'd like to respond.

IMHO, "cutting material on a cutting board" is not scientific enough. What's needed is the most uniform wear along the entire length of the blade.

I heard a couple times the "difference between having the test cylinder rotate".

The good thing about your test cylinder rotating is that you don't have any burr or wire edge "piling up" in the test media of a single slice. That negates artificial galling, which would be a huge variable.

I normally rotate the media (whatever test media- I like "Sharpies" best), because of this propensity. Especially final deburring and "destressing" (like "proving" an edge by using it).

Most people cut cardboard, which is pretty subjective, but making slices on hard plastic might be better. I like cutting manilla rope the best.

[Ken S]

Wadebevan,

Like you, I sharpen primarily my home kitchen knives. I appreciate the desire to create scientific, controlled testing conditions. However, I think we need to make allowance for the home kitchen. "Average" knife use is a bit like average temperature. I think is makes sense to test periodically, perhaps every couple weeks or before and after touch ups with a steel, etc. I am as interested in how well the knife sharpened on Monday works for Thursday dinner as initially.

Incidentally, I think you will enjoy your new PT-50A. My PT-50 is now the "vintage" model. It serves me very well.

Enjoy!

Ken

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Pavol Sandor has posted a you tube of a very clever continuous edge tester of his own design using rope. The you tube is in Slovakian, however, the video portion is readily understandable.

Ken

[Edgepal]

On a knife fair I find a steel producer that have made three knifes in three different modern hard steel for testing how the edges work and how they wear during normal use. The blades whas not similar thick and the edges had different edge angles.....

To come so close to sientiffic testreults as possible the edges must hold exact the same edge angle, if not - it is impossible to compare them.

Today can I adjust edge angles down to 1/100 part of 1 degree. My next step is to be able to control edge angles down to 5/1000 parts of 1 degree - and my goal is to come down to 1/1000 part of 1 degree with full control of the angle. When I have the time for it I shall sit sown and work with this.

How 1/100 part of 1 degree looks like on an edge can you se on my homepage Chef/precision grinding.

I like to se testnings of edges in different degrees, lets say how an edge on 20 degrees total edge wears compare with an edge in 22 degrees total edge - in different materials and in normal way of use.

Thomas