razoredgeknives wrote:


Ah Ha, the Professors papers resurfaces again ! Very Good ! I have quoted many times in other thread topics his classic definition of "sharpness"..

The problem is that "sharpness" is a very very hard word to get your mind and hands around. Definition of "apex sharpness" get confused in these discussions with "cutting ability" which are two different things.

As long as the edge is "straight" (whatever that means) and is vanishingly small, you have "sharpness:.

Josh, I know you are a member of the team that is working with me on the sharp-tester-jig. I am soon going to send out a condensation of many emails from that group, where these definitions are discussed in some detail: Here is an example quote that might be of interest:

As to the geometry of the bevel effecting how sharp the edge is,.. In theory, any angle from 1 degree to 179 degree could be made to be very sharp if the that point is vanishingly fine and straight. Of course, as a practical reality the real limits of angle are much less. (this is) point sharpness.., (this is not) "cutting ability" which is a whole 'nother world. If we were using the jig to test any form of "cutting ability" then we have to do something very different than thin tape that is pressed, without lateral movement, across the blade edge. ..... The mind exercise to visualize (testing sharpness or to answer the question 'how sharps is it?') .. can be stated as this: If the blade edge was infinitely sharp and the (material to be cut) was infinitely thin we would have a metric result of 100 on the scale, Anything that makes the blade edge less than that, or anything that makes the tape less than that lowers the number. The two factors interact. What we want to test and quantify is the deterioration of the blade as it goes less than infinitly sharp, we could do that if we had the right infinitely thin test tape, but we don't.

So, Josh, before you start discussing grit in relation to sharpness, you best get a firm definition of sharpness that you can center the discussion around. Most people do not understand, but 'whittling hair' is not a test of sharpness, it is a test the cutting ability of a blade to whittle hair. This is a subtle but very important distinction.

About what level of refinement is good for EDC use I've read 600 grit stones will get you a sharp edge that lasts. See here: bit.ly/MYhQsY

Clay, can't wait for the microscope pictures and the coming experiments!

Dan, thanks for the post. Those are excellent points... But in this thread I am not really trying to define "sharp" per say, just see if anyone can offer any experience or data to show that the edge of the edge does indeed get thinner with higher levels of polish or grit. And if so, will this degrade the edge quicker due to it being weaker?

Ben, thanks for that thread! That is very relavent to what we are discussing... It would appear that a course edge (i. E. Maybe 1k diamond) is more durable in the long run. Hopefully after Dan gets this "tester" done we can have some standards with which to test different kinds of edges!

BenBurke wrote:


Ben,

Thanks for the link. These discussion from 2005 that Cliff participated in are a very valuable reference, and should be required reading. It was around that time that Cliff coined the phrase "cutting ability" and spelled out in an understandable way several important concepts.

A quick note for you guys - I've also started an actual knife WIKI on this site, much like the actual Wikipedia and would like to begin populating it. I'm hoping to get some help with writing articles on everything from steels, knife history and construction, edge geometry, blade designs, abrasives, heat treating, sharpening theories etc... essentially everything knife related. The address is here: wickededgeusa.com/wiki/index.php?title=Main_Page. (Embedded link won't work so you'll have to copy and paste.)

razoredgeknives wrote:


well OK, it is perfectly OK to bring me back on track to thread discussions Now that we have this new topic area I feel a license to "drift off" a bit, but of course, that is not always appropriate.

So to address your specifics above I would venture to say that

1.) polish of the side of the edge positively may or may not make the apex become finer! It depends if the polish is applied in a particular way that continues to narrow the systems apex. It would seems that it is possible to just polish, abrade and polish, *only* the sides and never touch the apex. Then I would say you get no harm / no foul to edge longevity. In that case you potentially lessen frictional coeffiecients with the material being cut but there may be a trade off there as "stiction" is a real factor in material science. That effect when discussing knives I call the "cheese paradox".. it is the reason that a dull single wire cuts cheese better than a finely polished and very sharp razor blade.

2.) the degradation during use (slice cutting) of ever finer apex is really in the realm of, and up to, the steel in question. Can it handle it? some do some don't. That is why (see my previous post with the image link) that applications of things like Boron Nitride are very effective on keen edges on lesser steels. Of course super fine edges are subject (in the real world) to "rolling" and other deformations, so geometry also becomes an important factor. It is an interplay of factors, there are no easy "one size fits all" answers.