Unit for sharpness

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coyotes72

Joined
Feb 23, 2016
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We need to develop a unit for sharpness. It should have standards like s30v steel with 30 degree inclusive angle flat grind and mirror edge able to slice standard printer paper with a certain pressure. There should be different coefficients for different angles, levels of edge finish and other factors. What do you guys think, is it a good idea? Are the standards reasonable?


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Cliff stamp has been doing this kind of thing for awhile now . Long history I'm not going to get into but he does sharpeness measured in force and all that good stuff
 
I have a unit for sharpness.....

Sharp enough for me and what I use my knife for, I call it SEFMAWIUMKF units....

I suggest you take the advice above and visit the site metioned to see what an obsession with sharpness and geometry can do to you.....
 
coyotes72 said:
We need to develop a unit for sharpness. It should have standards like s30v steel with 30 degree inclusive angle flat grind and mirror edge able to slice standard printer paper with a certain pressure. There should be different coefficients for different angles, levels of edge finish and other factors. What do you guys think, is it a good idea? Are the standards reasonable?


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Here's a great link

It explains how to evaluate and test sharpness on hair.
http://www.coticule.be/hanging-hair-test.html

The blade steel is irrelevant, they can all get sharp with enough skill and time.
 
Several here have been using push cutting thread on a scale and measuring the load in grams. This is highly dependent on the type of thread used, and so it's difficult to compare from one tester to another. There is a BESS scale that is used by EdgeOnUp sharpness testing equipment, but it is basically grams as well. The advantage of the BESS scale and EdgeOnUp is that is uses a purpose made thread, so users with the same thread and apparatus can compare results.

The other way to test sharpness is by slicing light cord with a weight under tension. I have not tried this myself, as I have been mainly interested in push cutting sharpness (thread on a scale). However, the principle is to place a light cord under tension and make a slicing cut. The sharpness is measured by the length of edge required to make the cut, measured in inches or mm or whatever is appropriate. The shorter the edge needed and the lower the tension the cord is under, the higher the sharpness. For example, using a tension of 1 oz. and measuring a length of 0.25" to cut the cord.
 
coyotes72 said:
We need to develop a unit for sharpness. It should have standards like s30v steel with 30 degree inclusive angle flat grind and mirror edge able to slice standard printer paper with a certain pressure. There should be different coefficients for different angles, levels of edge finish and other factors. What do you guys think, is it a good idea? Are the standards reasonable?


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No. It doesnt make sense. What would be the variable? Different steels? Two blades prepared identically but with different steels will cut the same. Different levels of edge refinement? A better refined edge cuts better than a less well refined edge. Don't need a test for that. Different edge angles? More acute cuts better. Again, no test needed.

What is the variable being measured?
 
coyotes72,

Count me in !
I want to offer my services and expertise in creating units of calibration for cutting edge tools and scientific equipment. The photo bellow is but one example in a long history of such triumphs.

This is the scale invented and developed for the REAL WORLD TORQUE WRENCH. I am sure you will agree that it is infinitely practical for every day encounters with thready twisty things.


Just let me know when we can get together and invent the future.
Until then I will focus whole heartedly and one pointedly on this all important topic and will be in deep mediation until I hear from you.

 
As I'm sure others have pointed out, there are different kinds of sharpness, which is why we have different grinds to cut different foods or materials. Related to that is that some grinds can make a dull edge cut while another can make a sharp edge get stuck in certain materials. So I don't think talking about sharpness as a single phenomenon makes sense - it is actually a concept as complicated as the structure of the material being cut.

You could certainly create a series of tests to try to account for different types of cutting, but I'm willing to bet that such a system would predict performance that doesn't always match reality.
 
Its a good idea, but the variables are exponential.

I whipped up a test bed for retention, sort of a low budget CATRA that uses 3/8" manila but could use other materials as well.

https://www.google.com/url?sa=t&rct...YdR0p3zeYb7BhqLsWRu6NQ&bvm=bv.119745492,d.cWw

You can measure sharp by length of cut and load required, or amount of increasing force needed to make a pressure cut.

For best consistency I swapped coils of rope every 25 cuts and end for end every other. Variations in the rope were enough that it had to be taken into account.

Even if you decided on a reliable test media, you could only state with certainty how sharp it was relative to that media. It would also tell you nothing about longevity of the chosen edge finish.
 
I kinda use this scale butterknife(most non knifenuts blades), dull( no longer shave arm hair at all), need touch up soon(some pressure on skin and some hair cuts), sharp(light skin pressure cleanly shave every bit of hair in a patch), very sharp(hair popping off my arm with almost no pressure), treetopping sharp(arm hair slices just by the pressure of its hair folicle holding it upright, blade not near my skin). The last two is how high i sharpen to, any sharper is just too much work for how long the edge lasts.
 
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