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+--- Thread: Areas of Use and Limitations of the edge sharpness testers (/showthread.php?tid=191)
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Areas of Use and Limitations of the edge sharpness testers - KnifeGrinders - 10-27-2017
Question of where the EOU edge sharpness testers can be used and where not, has popped up too often through the last weeks for me not to bring it up here.
People seem to confuse edge sharpness and cutting performance testing.
Though there are other makes, a classic cutting performance evaluation tester is the CATRA Tester .
Here's how I see the difference in areas of use between the edge sharpness and cutting performance testers - and will appreciate your input.
Edge sharpness testers use a thin line test media, and the testing action is a point cut.
Cutting performance evaluation testers use a thick sheet test media with a wearing effect on the edge, and the testing action is a depth cut.
An edge sharpness tester tells you how sharp the edge is, which reflects only the 1st phase of cutting - penetration.
Edge sharpness tester scores have no bearing on the blade angle and profile because of that.
A cutting performance tester also tells you how effective the edge angle and blade profile is.
Edge sharpness testers have two primary purposes:
- monitor edge durability of the same blade over time;
- improve and streamline sharpening protocols.
Edge sharpness testers cannot be used to compare cutting performance of blades of varying geometry, and determine which one is superior to another.
Edge sharpness testers can be used to compare performance of blades of similar geometry but made of different steel.
I can put the same sharp hair-splitting edge on blades from 12 to 50 included angle, but they won't cut the same, and an edge sharpness tester can't tell me which will cut better.
Or can?
RE: Areas of Use and Limitations of the edge sharpness testers - grepper - 10-27-2017
Excellent post and good points Mr. KnifeGrinders. I agree. Sharpness and how well the blade will perform in various situations are different, but not necessarily exclusive. A dull blade will never perform well regardless of the bevel angle or edge finish, while a sharp blade may or may not perform well for a particular task depending on the bevel angle and especially the edge finish.
Sharpness must be established first as there is not much sense in messing around with a dull blade. Once a blade is sharp, the bevel angle and edge finish can be tuned to the task at hand. For instance, when slicing tomatoes and most general tasks a toothy edge will perform better and longer than a smooth polished edge. For chopping and push cutting there is not much advantage in a toothy edge.
Sharpness testing not only allows establishing initial sharpness, but also aids in determining how well a blade of different bevel angles and edge finish performs as it dulls.
Sharpness testing aids understanding of blade performance and edge retention. Performance to task and stress resistance are indeed different tests than sharpness, but nonetheless closely interrelated at all stages of stress and performance testing.
RE: Areas of Use and Limitations of the edge sharpness testers - KnifeGrinders - 10-28-2017
Let me rephrase the last bit.
Suppose I am charged to determine the best edge angle for each cutting task. How can I do this with Mike's tester?
We can plot scores as a function of number of cuts till the edge dulls for a range of edge angles, then limit the best angles to those satisfying the task, and exclude the rest.
Will that work?
RE: Areas of Use and Limitations of the edge sharpness testers - grepper - 10-28-2017
Sorry if I misunderstood your post. It seems to me that performance to task would require a different set of tests than just sharpness. Indeed, sharpness testing would be part of it such as establishing initial sharpness and monitoring sharpness along the way, but that would not answer the question of what is the “best edge angle for each cutting task”.
What exactly do you mean by “best”? For example, what angle requires the least cutting pressure, or what has the best edge retention/sharpness after a given number of cuts, or what “feels” the best to most people when cutting. That type of thing.
One type of test might be where a set amount of pressure is applied on a blade and then the number of strokes necessary to cut some specified amount of material is counted. That would answer one question. But then the question of sharpness retention over time could be considered. Maybe it’s better to start with a duller edge because that edge generally performs better, longer and therefore lowers long term sharpening costs in a production environment even though it may require greater pressure to cut at the onset.
So, I would think that it is necessary to define exactly what the initial question is before attempting to design a method of testing for it.
RE: Areas of Use and Limitations of the edge sharpness testers - Ken S - 10-28-2017
I think initial edge sharpness and edge retention are different concepts. Both are important. The Edge on Up testers are the most useful practical instruments I have seen to measure initial sharpness. The most useful tester for edge retention I have seen is designed by Pavol Šandor. Pavol has produced several excellent you tubes demonstrating his device. Even though I know no Slovakian, watching Pavol's you tubes I can fully understand his very useful device.
I believe a well versed sharpener should understand the difference between initial sharpness and edge retention.
Ken
RE: Areas of Use and Limitations of the edge sharpness testers - EOU - 10-28-2017
Hello KnifeGrinders, Grepper, Ken and all other interested parties,
This is a great thread so thank you. If you don't mind we'll chip in with our thoughts here. Instrumentation can be designed to test for very specific parameters and, in the alternative, very general ones. An emergency trip to the doctor might be a good example. If, upon examination, the EKG shows no indication of a heartbeat, the doctor is likely to cancel the patient's blood test. Blood tests can be important but, in the absence of a heartbeat, not really important at all. We look at edges in much the same way. We think that a properly sharpened edge is the heartbeat of a cutting instrument. If the edge on your chef's knife is dull, there's not much point in pondering the other geometric attributes of the blade. At least, not until you've sharpened it.
There is absolutely no doubt that the thinness or thickness of an edge apex (sharpness) is not the sole arbiter of how a cutting instrument will perform in a given task. Anyone who has attempted to chop a tree down with a razor blade can attest to that. In our opinion though, a designed sharpness level is the heartbeat of most any cutting edge. Designed sharpness level? Yes, an apex radius/width that has been designed for the task to be accomplished. The axe and the razor blade might be two good examples. One good and one bad for chopping wood and one good and one bad for shaving.
We're (EOU) believers in toothy edges but that was not always the case. We used to say "What do you want, a saw or a knife?" Toothy versus polished is a different discussion but still germane to this thread in this vein "Would you rather be working with a sharp saw or a dull saw?" Once again we find ourselves back at edge sharpness.
Now, after all this waxing, we'll finally attempt to contribute something here. We make a big deal in describing our products as being "a pure edge apex measuring system, independent of blade geometry". We're going to have to stick with that because that's just the way our stuff was designed. Our current mission is to answer one question, "how thick or thin (sharp) is the edge apex?" We're going to assume that a 4mm thick blade sharpened at 22 degrees is going to require more force to push through a pork loin than a 3mm blade sharpened at 15 degrees. We just don't know how much more. So, does our system answer all the relevant questions? Of course not. We do think that we provide a pure and non-obfuscated indication of the most important and the most relevant question, edge sharpness.
We've got some very smart and knowledgeable customers out there though and it wouldn't surprise us one bit if somebody devises a test that squeezes more info out of our systems.
Like we said, great thread and thanks for beginning it. Never hesitate to disagree in part or whole with EOU. We haven't thrown a tantrum for almost two weeks now. We've learned far more from our customers than our customers have from us.
RE: Areas of Use and Limitations of the edge sharpness testers - KnifeGrinders - 10-28-2017
Thanks for your input, friends.
Grepper, there is no confusion of yours - all you've said is what I've been thinking but was unable to word.
You've added a new interesting aspect of evaluation - the best sharpness for each task, since, of course, the sharpest is not always the best.
Am trying to make most of the edge sharpness tester in an evaluation, where other than edge sharpness parameters must be considered.
Suppose an abattoir wants to determine the best edge angle for each cutting task along the production line, to increase throughput while reducing frequency of sharpening and prolonging the knife life span, saving on the related costs. Though many operations are done with power cutters, they use several standard types of knives in each.
Slaughtering
Head & feet cutting off
De-skinning
Chest opening & evisceration
Carcass Trimming
Carcass Splitting & breaking
Boning
Subdividing cuts
Slicing & portioning
Skinning and gutting knives are good examples of when too sharp is bad.
When I check their professional knives out of the box, the boning knife edge angle is 40 degrees, cutting is 30 degrees, and slicing is 24-28.
So we already have an empirical angle range for these tasks.
I keep thinking of how a PT50 could be used for further improvement within that range. For example, will a boning knife of 44 degrees outperform the standard 40 degrees knife, or that will be a 36 degrees knife, but will it still satisfy the task?
You all have already helped with clearer demarcation of its area of use, am now thinking of how to better use it within that, or even beyond though indirectly.
Talking to other edge sharpness tester users helps better understand all that, and this forum is the best place for this.
I don't think we can just through a PT50 to a meet or poultry processor, and leave them alone with it, they need help with a methodology for their evaluations.
Similar with sharpeners, hobbyist or professional, with all the experience we have we could provide them with an explanation on how to use the PT50 to improve sharpening process.
Do you think it makes sense to start a new thread "How I use my sharpness tester to improve sharpening" for that?
RE: Areas of Use and Limitations of the edge sharpness testers - grepper - 10-28-2017
You have brought up exactly why performance/edge retention for a particular task is not only a difficult concept but also difficult to devise tests for.
Your question, “For example, will a boning knife of 44 degrees outperform the standard 40 degrees knife, or that will be a 36 degrees knife, but will it still satisfy the task?”, illustrates the point very well as it is a very specific, targeted type of use. I think that is excellent because it helps to define and limit the number of variables involved in constructing a test. Of course you could always throw in edge finish (more/less toothy/polished) into the mix just to confuse things and make the consideration of and testing of same more difficult or at least more time consuming.
Sharpness testing could be used to determine at what point a blade becomes too dull to use for a task regardless of the edge geometry. It could also help to determine how an overly sharp edge bends and rounds more quickly then a less sharp edge and therefore is not indicated. Of course that could change with the edge geometry. So you could end up with data indicating that for a 20° bevel angle, anything sharper than X is not productive, but for a 30° bevel the initial sharpness might be something else. It can get really complicated when you start to think about it.
That’s not to say that less detailed results are not helpful. After all, we are considering animal disassembly by slicing and hacking with basically crude tools, not slicing samples for microscopy slide prep. So it very well may be helpful and advantageous just to be able to say that, generally, for a boning knife, a 25° bevel sharpened to 200 gf initial sharpness works well with overall good edge retention for most situations.
It’s a cool subject and needs a lot of exploration. I hope you continue to post your thoughts on the subject.
“Similar with sharpeners, hobbyist or professional, with all the experience we have we could provide them with an explanation on how the PT50 is used to improve sharpening process”
I agree. Shared experience as well as handy tips and tricks is always useful, especially for someone new to the game.
Do I think that it “makes sense to start a new thread "How I use my sharpness tester to improve sharpening" for that?” Yes! New threads are a good thing. So often thread subjects morph into totally different subjects. Better organization is always a good thing.
RE: Areas of Use and Limitations of the edge sharpness testers - KnifeGrinders - 10-28-2017
Thank you. I am after a high-level understanding in this thread, and this is exactly what I am getting from you.
RE: Areas of Use and Limitations of the edge sharpness testers - me2 - 12-07-2017
One area of limitation I've thought about is the difference in edge type and use vs how the sharpness is measured by the EOU testing equipment. For example, I tend to do more push cutting during use. This comes from breaking down boxes when I worked at a grocery store. For that type of use, high polish and low angle worked well. This is also the way the EOU testers work, by pushing straight down into a medium and seeing how much effort it takes to cut.
However, for those that use more of a slicing motion, and coarser edges, it seems it might not be the most representative test. Don't get me wrong, I've had coarse edges that had very high push cutting sharpness, but it seems it might be like testing a hacksaw by trying to plane a 2 x 4. I've seen some tests used that were for coarse edge slicing ability, but they are not standardized.