Sharpening Stainless Steel and Japanese High Speed Tool Steel
- This topic has 67 replies, 8 voices, and was last updated 10/14/2017 at 9:05 am by
.
-
One of the things I hope to accomplish with the new grit chart is to include the sharpness results. We will probably have a some sort of legend which will indicate if a knife finished with that grit at n° will:
All those tests are for cutting material accross the blade. Would be interesting also include results of slicing material along the edge. Like distance that blade travels to cut through tomato skin. The knife weights should be equalized to have the same pressure. I am kidding. 🙂
5 users thanked author for this post.
Sharpness is a really difficult quality to systematically quantify. We all know it when we feel it, but actually putting a number to that sharpness so that it can be compared to another sharp thing is not trivial.
4 users thanked author for this post.
Even if you were to use a clamped knife in a mechanical measuring device, just because it tests sharper scientifically measured with a calibrated device, doesn’t mean it will feel sharper and perform better when doing a real-life cutting activity. That’s when shape and profile and weight and balance come into play. I’ve done several paper cut tests where newsprint was cut with a “whisp”.  But when I cut food it felt like I had to push more excessively than what would have made sense for the sharpness of that knife.
Marc
(MarcH's Rack-Its)4 users thanked author for this post.
Sharpness is a really difficult quality to systematically quantify. We all know it when we feel it, but actually putting a number to that sharpness so that it can be compared to another sharp thing is not trivial.
Even if you were to use a clamped knife in a mechanical measuring device, just because it tests sharper scientifically measured with a calibrated device, doesn’t mean it will feel sharper and perform better when doing a real-life cutting activity. That’s when shape and profile and weight and balance come into play. I’ve done several paper cut tests where newsprint was cut with a “whisp”.  But when I cut food it felt like I had to push more excessively than what would have made sense for the sharpness of that knife.
Agreed. At best we can set some benchmarks to show the performance of a specific grit at a specific angle on some common tasks. Taken alone, the information wouldn’t be very helpful, but shown in a progression, it might be helpful for people to be able to see that at x finish, the knife needed n force to make the cut or was able to pass HHTn, but then with one more stone/strop/film added, the force required to cut dropped to n grams or the knife edge now passes a new HHT level.
-Clay
Sharpness is a really difficult quality to systematically quantify. We all know it when we feel it, but actually putting a number to that sharpness so that it can be compared to another sharp thing is not trivial.
Even if you were to use a clamped knife in a mechanical measuring device, just because it tests sharper scientifically measured with a calibrated device, doesn’t mean it will feel sharper and perform better when doing a real-life cutting activity. That’s when shape and profile and weight and balance come into play. I’ve done several paper cut tests where newsprint was cut with a “whisp”. But when I cut food it felt like I had to push more excessively than what would have made sense for the sharpness of that knife.
Agreed. At best we can set some benchmarks to show the performance of a specific grit at a specific angle on some common tasks. Taken alone, the information wouldn’t be very helpful, but shown in a progression, it might be helpful for people to be able to see that at x finish, the knife needed n force to make the cut or was able to pass HHTn, but then with one more stone/strop/film added, the force required to cut dropped to n grams or the knife edge now passes a new HHT level.
I look forward to seeing the data once it has been collected and tabulated. My prediction is that if you plot the average scratch width of the finish versus the force needed to cut the test material it will yield an asymptotic trend. It would also be interesting see a plot of force required to cut a test medium as a function of sharpening angle with a fixed sharpening progression. Yes, I am a nerd.
3 users thanked author for this post.
Here’s the problem in trying to quantify sharpness as I see it. Take one knife made of a certain steel, now take the same knife offered in a different steels, now consider how many different knives their are and all the different steels, the combinations are almost endless. Then consider that each “batch” of steel has different qualities and characteristics all though they are called the same steel. A metallurgist can identify steels that are produced by each individual batch of steel even though the intention by the manufacturer was 2 identical batches of steel. The time to chart all this would be bordering on insanity and never ending, in my opinion. Very early on I realized that every individual knife has an edge waiting to be discovered. I believe it is my job to find the edge in that particular knife that compliments the geometry of the blade, the material it’s made from, its intended use, the person that will be using or abusing it, and in the case of a quality knife, of a master smith, the edge they envisioned for it (that’s the purest in me). As stated by MarcH, the best test, in my opinion, and I believe the only test that really matters is the test of use in the hand of the person that will be using it as stated by Organic as well. That and time.
Some knives work better for what they will be used for, ie “feel sharper”, at a 600 grit finish with light stropping. Others benefit from more polished and more refined edges. Even the expensive Japanese knives that cut the intended material whisper smooth and paper thin, and by the way don’t come with a remarkably refined edge as MarcH has shown in so many photos, may not benefit from what I consider to be an “over refined edge”. Some large knives that will be cutting harder, denser material may benefit from a 200 or 400 grit edge. A straight razor seems to benefit from a micro convex edge to get rid of the burr as much as possible. So each edge will “feel” sharper if sharpened for it’s purpose, in the proper manner, with the proper technique, not just it’s refinement.
I guess what I’m trying to say is sharpness is not just how far you can refine an edge. but what the use is and how it will be used is a determining factor as well. So I don’t believe “sharp” will ever mean the same thing to any 2 knives or any 2 people. In my opinion it’s not something you can scientifically quantify unless you have identical knives, with steel from the same batch, and sharpened at the same time, and even then I don’t think it’s a fair test. I haven’t even addressed the stones and how they change with the user, amount of use, material they are used on, so on and so on.
Yes there are things that we can share that make us better at this craft, but it’s how and when we use the methods and techniques that determine how a particular edge will benefit. Some methods and techniques benefit the edge of certain knives more than others.
I’m just expressing my opinion on this and it’s not my intention to insult or offend anyone. I do believe, and I myself am guilty of this at times, we are looking for absolutes in something that doesn’t have many absolutes. Thanks guys and sorry if this turned into a rant.
Well said! I do think that sharpness can be quantified if there are enough constraints on the cutting task, but even then the data will only be directly correlated to that specific application. Once you switch from measuring force required to push cut a string to force required to slice the a string the numbers and rankings of which blade is sharper might change dramatically.
I think one thing we all can agree on, when we pick up a knife and cut with it, we know what sharp is and how it feels, and we know if that knife we just cut with, is sharp. “Which is sharper”. Ah? That’s a tough one.
Marc
(MarcH's Rack-Its)
- You must be logged in to reply to this topic.