Knife Sharpness Scale

I like the idea of quantifying the force to cut.

My feeling is that your measurement reflects the keenness of the blade which is only one aspect of cutting performance. However, some data is better than no data.
Probably the Boffins at Gilllete and I are the only ones who have the ability to directly measure and quantify the edge geometry, so a simple and inexpensive testing apparatus is appealing.

I would suggest that an impartial evaluation of the apparatus is required. Send one to Cliff Stamp - I'd be interested to hear what he says about it.
 
Hopefully you remained tuned into this thread Todds. Would you mind if I emailed you with regard to some of the matters you mentioned in your post?
 
Well looks like we are running out of steam here so I would like to thank everyone who has participated in the thread to date and in so doing point to the Todds post as one that, to my my point of view, summarizes the function of the scale/instrument quite well. My feeling is that your measurement reflects the keenness of the blade which is only one aspect of cutting performance. However, some data is better than no data. And true it is. My mercury thermometer gives me the current air temperature. It won't calculate the windchill however. To me, that portion of the blade that first contacts the medium to be cut, sliced, chopped, etc. is a critical factor in how the blade's performance will be judged by the operator. Sort of "where the rubber meets the road" in my thinking. I opened this thread with my comments about a sharpness scale (BESS) and if this thread's interest level has expired then I would like to close with the BESS as well. The BESS gives us an opportunity to move from using terms like "tomato sharp" and "scary sharp" to describe sharpness levels to quantitative descriptors like 129, or 182, or 790 with all these numbers being equated to the relative and general sharpness level of a double edge razor blade with a BESS value of "0". Is the instrument/BESS the be all end all of cutting/slicing efficacy determinations? Of course not. It is, in my opinion however, immensely superior to slicing up tomatoes and paper from a quantitative standpoint. Perhaps next time you and I communicate you won't tell me your knife is "scary sharp" but rather a 75 on the BESS. Now that tells me something.
 
Isn't it much simpler to just simply say how wide the primary edge bevel is at the top???? I hardly ever see this information in any review, and that is practically the only thing you really need to know... At least that is all I need to know to have even a vague idea of what I can make out of a knife... And then to mention, as a side note, the angle of the primary bevel (just in case your sharpening abilities means it still matters)...

And people wonder why Randalls are so popular... Maybe it's because they're the only large fixed blades with a deep hollow grind ending with an edge bevel top that is half a milimeter thick, which means it will remain sharp for decades as it wears up... And being a knife guy for decades, I had to buy a Randall to finally find this out... We sure are completely swamped in useful information I tell you...

Gaston
 
Well it looks like this thread still has some life and that's a good thing. If I understand your proposal correctly you're asking why couldn't sharpness of the edge simply be expressed as a measurement of the thickness of the apex of the edge and that would, in my opinion, be a wonderful thing indeed. The question in my mind is how is that measurement made? Back in my fiber optic sensor days we used to measure the apex height (not width) and other symmetry factors of polished fiberoptic connectors with an interferometer but of course that was a $30,000.00 instrument. My understanding of the thickness of very refined edges is something in the hundreds of molecules range. The theoretical claim for cleaved obsidian is something like a single or ten molecules dependent upon who and what you read. Do you have a measurement system in mind or have I misunderstood your proposal?
 
The primary edge bevel at the top, or if you prefer, the base of the bevel... Since bevels are usually depicted edge-down, I choose to say the top... So I meant: How wide is the bevel at the primary grind line... This crucial information usually appears absolutely nowhere (even though it is practically the only information that really matters with regards to an edge's initial performance)... Even after decades of reading about knives, I only found out by buying them that Randall knives were the thinnest V-edged factory big blades at the base of the edge bevel (not counting my 20 years out of production Al Mar "Special Warfare"): 0.5 to 0.6 mm on a simple caliper... (Most other thin-edged big factory blades being convexed, like Blackjack and Bark River, these don't really count as competitors to Randall for me).

This might explains how roughly finished (and often crookedly made) Randall knives are so treasured (mind you, the handles are usually very nicely done): Thin half-milimeter V-edge bevels on their hollow grinds means they will be easily sharpenable to the same level of sharpness for generations of owners, however crooked and wobbly their other blade grinds are (not to mention the usually awful amateurish finish, full of various strange swirls that -fortunately for Randall- don't really show up in photos)...

Yes I know, convex edges don't really have an edge bevel "base", but at any relevant point, put a triangle inside the convex edge, and you get the basic sharpness vs lateral strenght geometry (allowing you to ignore temporarily the diminution in sharpness that the "fatness" of the "convexing" added), making it easy to deduce the actual true sharpness potential, if you were to not fully re-profile the entire thing... With the basic convex geometry established, you will know what the "formerly" convexed edge is capable of with just minimal flattening of its sides into a proper V shape (still a bad ordeal mind you, but not as terrible as a full re-profile)...

It really is irrelevant what finish you put on that V bevel: Your choice, but knowing the basic dimensions of the bevel's triangle means you know what you are starting with, performance wise, before ever going through re-grinding that edge, or buying the thing in the first place... And somehow that basic info, obtainable in seconds with any caliper, is never presented anywhere...

Gaston
 
OK I think I have it now and sorry for my earlier confusion. I think, in principle, that you have a very valid idea. Once again your thought process has some applicability to the laser/optics industry in that if you want a very small spot size you better start off with a laser diode with an equally small active area or "point source" as it is known in the industry. My personal but less than scientific observations in the edge business tells me that the thinner starting point of the edge to be ground the sharper or more acute the finished edge can become i.e. razor blades.
 
While the forum posts seem to be few the emails have been many so I am going to try and clarify a few things in a sort of mass way. The first issue is test media. BESS certified test media is under the province and control of BESS•U. No matter who the instrumentation manufacturer may be if they invoke the BESS or claim BESS Certified on the instrument then they must utilize BESS certified test media. This, of course, keeps everyone on the same page sharpness data wise. The second point of confusion seems to surround the question of the test methodology and I am going to borrow from a communication (redacted and paraphrased) I was copied on from one of our sharpness testing instrumentation manufacturers with his explanation. I believe that most of this has already been covered in bits and pieces but here it is in concise form;

Thank you for forwarding John's comments. While this particular area is well outside my training and well inside John's I think there is the possibility that we may have managed to convey the wrong picture to John with regard to the measurement mechanism and how it functions.
From the outset it was the intent of BESS•U to develop a pure edge sharpness test media and method that would not be significantly affected by either sharpening angle or blade geometry. While we understand that these other factors may certainly affect the overall cutting ability of the blade in general use they were not intended to enter our equation. I have previously given you the analogy of a mercury thermometer. It just gives you the temperature - not a wind-chill calculation. The instrument and test media operates under the presumption that the blade geometry has already been set so all that remains to the user is to refine or maintain the edge already defined by the blade manufacturer.
Our test media is .009" in diameter and was developed so that it shares some of the same characteristics as a glass fiber optic fiber with regard to it's shear characteristics. As you may know fiber optic fiber is cleaved rather than cut. The outer cladding is scratched and then only slight pressure need be applied in order to sever it cleanly and completely. This was the sort of severing action that we sought in the development of the test media. I'm not at liberty to describe the exact makeup of the test media but hopefully this lends a little more clarity to our intended design goals.
It is our thinking that with a test media diameter of only 9 thousandths of an inch in combination with our designed shear characteristics that we are testing the extreme apex of the edge only. . If one were envisioning something down the lines of a CATRA for example it would certainly be understandable how the methodology could be misunderstood. Assuming that I have interpreted John's remarks correctly then this would not represent our first failed communication event with regard to this matter. We need to do a better job of communicating our test methodology so that potential users are able to connect the dots.

So there you have it forum members and guests. If you still have questions both this thread and my email remain open.
 
I would talk to the folks at wicked edge about this whole sharpness thing. Clay and the gang have it down pat IMHO. That being said I dont see many manufacturers going for this type of certification, as not all blade shapes or styles lend themselves to cutting very well (See Striders tanto blades). Personally the only manufacturer I have seen that ships a stupid sharp nife is medford knife and tool.
 
CharlieSoxx said:
... and 55 for my straight edge razor. ....
Click to expand...

If I understand correctly, that is a total of 105 grams on a 225 micron diameter filament. That seems like a very high pressure for a delicate straight razor edge.

Have you looked at the edge of the razor after testing with a microscope to see if there is visible damage?

I would expect a properly honed straight razor to require less force than a DE blade, not double....
 
Sorry for the delay in responding but have been out of town. The sharpness test is nondestructive. I cannot speak to what tests the instrumentation manufacturers have conducted relative to that design issue but I know that ten minutes experience with the device will demonstrate from a practical standpoint that there is no damage to the edge via the testing process. It seems though that I read or heard in a meeting at some time or another that repeated tests at a single point will begin to dull the edge of a DE razor blade. I've never taken enough tests on one blade to witness that phenomena myself but it does sound logical.
 
Sorry, forgot to address all of your questions. I mean this in my most earnest attempt at levity - "who said that my 55 represented a properly honed straight razor?" I would love to hear from other straight razor users (not like me but the guys who actually know how to hone a razor) what measurement levels they are able to achieve. While there is little doubt that they will be able to surpass my efforts I would be surprised (but I've been surprised before) if they could surpass the sharpness level of a DE blade.
 
Well, I certainly am a common man so I hope that I can be forgiven my misconceptions. I'm going to move on from this thread now, hold the applause please, and move back to the industrial and research arenas where I can pick up again on my proselytizing for the BESS sharpness scale. Before doing so I would like to expand on this post's "common" theme. I have read much from some quarters regarding the question "What is sharpness?". Without a doubt BESS•U.org and our instrumentation manufacturers subscribe to the commonly held notion that a razor blade is sharp and a butter knife is dull. The most notable physical factor separating these two objects with respect to cutting efficacy is the thinness of their respective edges. If you subscribe to this theory as well then Bess certified test instrumentation in conjunction with BESS certified test media is your ticket. Your bonus will be a means of collecting and then communicating sharpness data in a clearly understood and quantifiable manner and to do so with those who do not even own an instrument. My personal email attached to this forum remains open as does that of BESSU.org. Thanks to all for your input and interest in BESS.
 
ToddS said:
I like the idea of quantifying the force to cut.

My feeling is that your measurement reflects the keenness of the blade which is only one aspect of cutting performance. However, some data is better than no data.
Probably the Boffins at Gilllete and I are the only ones who have the ability to directly measure and quantify the edge geometry, so a simple and inexpensive testing apparatus is appealing.

I would suggest that an impartial evaluation of the apparatus is required. Send one to Cliff Stamp - I'd be interested to hear what he says about it.
Click to expand...

Todd, would you be willing to provide measurements on Feather DE razor blades? Shoot me an email, I'll have a 50-ct pack shipped to you if you'll feed my curiosity :D
 
bpeezer said:
Todd, would you be willing to provide measurements on Feather DE razor blades? Shoot me an email, I'll have a 50-ct pack shipped to you if you'll feed my curiosity :D
Click to expand...

The Feather DE is relatively keen, but not as keen as the Feather Artist Club blade or a blade in a Gillette Fusion cartridge. The PTFE coating gives it some cutting advantage beyond geometry alone.

There is Feather DE blade midway through this post: https://scienceofsharp.wordpress.com/2015/03/24/sharp-and-keen-part-2/
 
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