Sharpness Chart

[wootzblade]

Having been using the edge sharpness tester from Mike Brubacher for two years, I don't shave forearm or do hanging hair tests anymore, as the BESS score itself tells me everything.
These traditional tests are no more than historical for me, but I will always be feeling sentimental about them as they've been the only means guiding my sharpening for decades.
But as fellows not having the sharpness tester kept asking for some guidance, I did these measurements for them.
The BESS and apex width values I give for these tests is the earliest attained sharpness (from the dullness end of the range) when the test can be performed more or less cleanly.
And let me re-iterate that the instrument reading - the BESS score, tells the edge apex width only to a first approximation for these "traditional tests".
As our knife community feedback was overall positive, we did a more thorough series of tests for the Australian Knife Magazine.

The tester accuracy is very high, repeatable and exact when done under controlled conditions; so accurate that detects difference in sharpness of DE razors of different brands, e.g. it clearly distinguishes a Feather razor from Gillette.
Feather razor scores 30 BESS, i.e. about 0.05 micron edge, while Gillette scores 40-50 BESS i.e. closer to 0.1 micron edge.
Check for example the razor study done with this instrument by Chase Anderson at https://www.refinedshave.com

I have no need to convince anyone, as I've built my sharpening business on these testers and our computer software, streamlined our sharpening protocols, and we now do volume sharpening 5 min per knife bringing each edge to 0.1 micron edge apex width for mainstream brands, and near 0.05 micron edge for high-end.
Note that the Gillette razor has 0.1 micron edge.

We've made these data available for everyone outside Australia, because we feel ourselves a part of the wider knife community.
It would be a shame to keep them to ourselves only.

 

[miso2]

I am interested in knowing how the BESS score is related to the edge width.
If it is a simple conversion of the force required to cut a material to the contact area, rough edge ridges (toothy edges) may work better than smooth ridges at the same edge width.
Or, has it confirmed with electron micrographs, like ScienceofSharpness does?

 

[wootzblade]

BESS Score - to - Edge Width correlation is true in the scale range from 10 to 400 for a polished edge of finer-grained steels and CPM; but not for ragged edges and edges off a coarse grit with pronounced toothiness. The correlation was established by matching the sharpness score to the direct SEM measurements, and BESS sharpness testers are calibrated to show edge apex radius in nm.

This sharpness tester is spot sampling.
Though a BESS calibrated edge sharpness tester is a great tool to determine the degree of sharpness, by itself it is not sufficient to verify quality of the whole edge as it samples only one point on the edge, even when you take a couple of measurements at its different portions.

At Knife Grinders we check edge by two devices used together: a BESS PT50 edge sharpness tester plus Razor-Edge edge tester.
While the BESS sharpness tester is spot sampling, the Razor-Edge edge tester checks condition along the length of the edge, and used together, they give pretty comprehensive idea of the whole edge quality, and this tandem is our QA method at the end of each sharpening session.

Yet, measuring the edge sharpness with the PT50 tester alone at the same spot on the edge will suffice for guiding your sharpening session in the right direction.

For example, how we use this BESS edge sharpness tester in honing.
We keep honing while the sharpness score keeps improving (i.e. lowering), and stop when the reading has stopped changing.
At this point, should you continue honing - you will lose the edge sharpness you've just achieved.
At this point the right thing to do is either to change to a finer hone, or just enjoy the best attainable sharpness you've already got.

Want your edge to shave - hone it to 150 BESS, but want it to split a hair - change to a finer grit and continue honing to about 120-90 BESS, and then change again to the finest grit and go on honing to 70-50 BESS.

The BESS edge sharpness tester indicates those breaking points in the sharpening sequence, where you have to change to a finer grit, and not to ruin the edge by overhoning.
You know you are overhoning the edge when the BESS reading increases.
When I see this, not only I change to a finer grit, but may also take a shallower honing angle.

We use computer software to control angle of grinding and honing with 0.1 degree accuracy, that allows us to maintain the same edge angle through the whole sharpening process.

 

[HeavyHanded]

So what you are saying is that this system only is really appropriate for testing push cutting, and therefore an edge that would excell at push cutting will excell at this test? So a refined smooth (not toothy) edge is going to score high here even if that edge isn't necessarily ideal in real world use.

Personally I find that looking for light reflecting off the edge is not a very good way to test sharpness. Especially because I am often sharpening in different lighting conditions. I also find it hardest to see what is going on when I am sharpening with a strong overhead light. This is because as I lay the edge flat on the stone the edge reflects the light back making it difficult for me to see.

I use a combination of laying the edge on my finger nail and trying to drag it to one side and then the other to see if it is only catching in one direction. (Rolled edge) I test this up and down the edge. I also slowly slice a piece paper to test the edge for chips. I make sure to drag the edge from heel to tip. If the paper catches that is likely a chip. Those areas get a little extra love.

Exactly.
You can set the testing line on the edge and give a slight pull - the line severs. You can reduce the amount of load and repeat. You'll find the amount of force needed is much lower than the amount needed to pressure cut. In many cases there is an inverse relationship between the two - up to a point.

It tests for a certain kind of sharp, is not predictive of how a given edge might actually perform.

It IS a very well-thought out unit, and would be very helpful in context. For EDU and utility work, not so much.

From what I was able to tell using an optical microscope, ALL sharp edges are submicron along much of their length. Level of refinement = reduction in variation along and across the edge. Very rough edges will have greater % that is not submicron, but on the whole a large percentage will still be mighty thin at the apex.

 

[wootzblade]

Before out study, the only available definition of the demarcation between sharp and dull was Steve Bottorff's "Any edge thickness under a few thousands of an inch could be considered sharp."

I know Steve very well through the Tormek forum, he even personally signed to me his "Sharpening Made Easy" book. He's an honest man, and won't be insulted when we correct him that by our findings, sharp actually starts from tens thousands of an inch edge thickness. Our numbers for "sharp" differ from his by one order of magnitude; when Steve did his estimate of sharp he simply didn't have the equipment and SEM data we have now.

I am proud that it's us Australians who rewrite this critical number defining sharp the whole inet refers to.

 

[wootzblade]

Practical use of these sharpness tests is not as much to determine the already attained sharpness, as to guide your sharpening process.
Some tests are more useful than others as they tell you when you have to change to a finer grit.
Certain sharpness tests are so precise that tell which grit number to choose.

I compiled this Sharpness Chart for those who haven't got a sharpness tester yet.
You can pick tests from this chart, and build your own system of indicators telling you when you have to change to a finer grit in refining your edge.

 

[BluntCut MetalWorks]

Wootzblade - thanks for sharing this sharpness chart. Nice to see a thoughtful compilation of overall a sharp edge can cut/separate correlate to apex width (in microns). Also glad it was done with attempt of high regard for technical and scientific principles.

jpm2 brought up good points about edge-light-reflection test under different light intensity. Perhaps to keep thing simple, your explanation about visible light doesn't reflect against a sub 400nm apex width. This explanation is incorrect. Without a doubt, there are light reflected back to eyes for dull to ultra thin apexes, whether to see/register depend on quantity of received photons. Visible light easily goes through 50nm wide slit, albeit none-aligned-component of (polar/orientation) EM waves are blocked. jpm2 is correct - doesn't matter how sharp (in sharpening context), edge is visible given enough light.

Complexity instantly goes up when more accurately we use 'radius' instead of 'width'. Light deviate/scatter much more drastic/steep against diverging curve surface (e.g. a rod).

What is BESS test thread consistency and granularity? From older BESS thread, I saw image evidences of wedging & binding, so 'granularity' is at least an order of magnitude in size compare to apex width, therefore inconsistent = consider as none repeatable in science. HeavyHanded/Martin & others showed evidence of this aspect of high carbide volume steels got extra high sharpness score when apexes these edges are highly irregular.

 

[wootzblade]

I agree with everything you say.
All these tests and checks, including for light reflection by the edge, are no more than rough checkpoints, to guide the sharpening process in the right direction.
But it's better than nothing for those who haven't got some sharpness measurement instrument giving objective checkpoints.

Here in Australia we work on matching these "traditional sharpness tests" to direct SEM measurements, but do not expect an update too soon, as we do this of pure curiosity and this is not at the top of our priorities.

The BESS PT50B edge sharpness tester covers all my business needs in developing sharpening protocols for each type of steel we have to sharpen, and to streamline them for volume sharpening. We don't even talk microns or edge width anymore, just BESS numbers.

 

[wootzblade]

Cigarette paper test - slice the edge furthest from fingers holding the cigarette paper horizontally, then push-cut down.
Becomes possible at 30 BESS or 0.06 micron edge, but cleanly performs only at 20-25 BESS or near 0.05 micron edge - requires the same level of keenness as the top hanging hair tests.

The vertically held cigarette paper requires less sharpness at 110 BESS, i.e. about 0.2 micron edge, which is close to "scary sharp".

This one is a highly precise test due to standardized "test media", and I replaced with it the toilet paper test in the sharpness chart on our website Sharpness Chart >>
I never took that single ply toilet paper or facial tissue tests seriously anyway.

The only knife in my collection that passed the cigarette paper test held horizontally was a CRK Umnumzaan Tanto.
It scored anywhere between 20 to 40 BESS on the tester, and with that much dispersion I had to resort to other methods to determine the exact sharpness needed for this test.

I used a number of DE safety razors of various brands, slightly differing in sharpness, and Wilkinson Sword was the only brand of those I have that could do the cigarette paper test more or less cleanly.

When I need ultimate precision, I use a guillotine I built for the PT50 edge sharpness tester. It gives highly reproducible readings at the threshold of the instrument resolution.

The Wilkinson Sword safety razor scores 29-30 BESS in this controlled measurement.
This allowed me to finally conclude that the minimum sharpness needed for this test is 0.06 micron edge, but to perform it cleanly - 20-25 BESS or 0.05 micron edge.

I've been told the Tally Ho paper is thinner than many other rolling papers, and 10 times thinner than a human hair.
I've also found out that sharpeners in a number of countries do use cigarette rolling paper for knife sharpness testing due to its uniform standard.

The Tally Ho cigarette rolling paper test is destined to become common with every sharpener.
Horizontally held - for high-end knives and razors, vertically held - for kitchen, butchers knives and alike.

Since this test requires the same level of keenness as the best hanging hair tests, it is a good alternative to the HHT.
It is actually a better alternative, because human hair aren't that uniform as this paper.
Definitely better than pulling out your own hair for HHT, especially when you are of my age and hair are in deficit.

 

[wootzblade]

BTW looking for names of degree of sharpness for this chart was a true pain and fun at the same time.
I had to dig knife forums all over the inet for hours to get those fanciful terms the knife community uses to describe sharpness.
"nuts, scary, crazy, wickedly sharp" etc
None of them are academically endorsed, but obviously full of meaning for those using them.

 

[scottc3]

Wow, Thank you for bringing this set of information, might I call it new tools, to my attention! I'm a primitive, push cutting various papers (20 pound copy paper, lined school binder paper, catalog, phone book...) to test edges with no attention paid to discern media variations or pressures (grasping hand nor pushing).
One of the fundamental take aways I remember from a year of upper devision undergrad neurology, was our measured ability to accurately predict weight variations with our hands and pressure variations with our fingers was not exactly "well developed", not withstanding our experiences of love, work and play. This body of knowledge is not pursuit of perfection as it is establishing the utmost practical edge...
And it needs to be said, what accident of history prevents knife companies from establishing mass producible consistent edges with machines that match those made by guided systems... maybe it's just the lawyers... and the nanny state; after all who of us does not already have a mother?

 

[maximus83]

I agree with everything you say.
All these tests and checks, including for light reflection by the edge, are no more than rough checkpoints, to guide the sharpening process in the right direction.
But it's better than nothing for those who haven't got some sharpness measurement instrument giving objective checkpoints.

This is exactly how I'm using it. The informal sharpness tests, and clarification of the terminology into a consistent hierarchy, are tremendously useful. Example: I just used the thumbnail test, then the receipt paper test with a newly sharpened edge to test slicing off chunks with grain, cross-grain, then doing both push and pull-cuts, with grain and cross-grain. That blade is more than factory sharp and good enough for EDU purposes, and I don't have to keep shaving my forearms bare to prove it.

Thanks for putting this together!

 

[wootzblade]

Thank you, mate.
There is a chance you may get the Tally Ho cigarette rolling paper as well from your local tobacconist.
Though it is called "Australian famous" and we have it in every supermarket under $1, it is produced in Belgium.

If not, tell me what is the common cigarette rolling paper at where you live, and if it is available in Australia, I will test it for you.
I've been told that Rizla lightweight rolling papers would be close to our Tally-Ho brand for paper thickness. Rizla should be available worldwide, I can test it for you if you have it.

 

[Alberta Ed]

What is it when you whittle electrons off atoms to create new isotopes?

 

[wootzblade]

New level of sharpness achieved at Knife Grinders!

Having improved our sharpening protocols based on SEM data studies,
we now steadily get the same or better knife edge sharpness as the Feather DE safety razors.

For quality mainstream steel, from Global and up, the edge sharpness is 20-35 BESS or near 0.05 micron edge apex width.
For premium high-end steel, the edge sharpness is 15-20 BESS or under 0.05 micron edge apex width.
Note that the Gillette DE razor has 0.1 micron edge and scores 50 BESS.

An edge that sharp easily passes the top hanging hair tests.
This level of sharpness is extraordinary for knives, and is more readily achieved by dedicated straight razor sharpeners.
We now get that sharp edge practically at a volume sharpening speed.

More details on the BESS forum:
http://www.bessex.com/forum/showthread.php?tid=209&pid=1613#pid1613

BTW the Sharpness Chart has been updated, and as I know some of you have saved it onto your computer, just check you have the final version.

 

[maximus83]

New level of sharpness achieved at Knife Grinders!

Having improved our sharpening protocols based on SEM data studies,
we now steadily get the same or better knife edge sharpness as the Feather DE safety razors.

That is impressive if getting that level of sharpness on a knife blade. I use Feather DE razors, they are the sharpest razors I've found.

 

[wootzblade]

Thank you mate, yes it is a true breakthrough. Especially for a volume sharpening, within 5-10 min per blade.
Has only become possible on the shoulders of such a giant personality as Todd S and his scienceofsharp.wordpress.com data.

Note that this is on CBN wheels.
We haven't finished our tests with Japanese wheels, and don't know yet if the same extreme knife sharpness can be achieved on them with the same high speed.

 

[kreisler]

Thanks for the chart, very good!

 

[Wowbagger]

I feel there's way too many variables when it comes to edge reflecting light vs sharpness unless the exact conditions are stated, and can be duplicated by us laymen.

What light source, How bright? What background, How dark? Is that with uncorrected 20/20 vision, and/or under magnafication?

I was sitting in the sun in the back of the house. The sun was coming through an open window with a screen. Pretty high here (~7000 ft elev.) so intense sun. I finally remembered to try the refection on the shave sharp edge thing.
I had on a jeweler's visor with the strongest lens.

I tried my M4 edge to shave arm hair. Though it hooks up on my thumb nail the only part that would shave was near the choil.
I could see slight refection along the length of the edge except where it was shaving sharp. Almost no dings; just the ever so slight change in reflection width in places.

I don't doubt it will reflect and shave but I didn't get that result yet. My dark back ground was the inside of a black sintho. fleece sweater.

 

[jpm2]

I was sitting in the sun in the back of the house. The sun was coming through an open window with a screen. Pretty high here (~7000 ft elev.) so intense sun. I finally remembered to try the refection on the shave sharp edge thing.
I had on a jeweler's visor with the strongest lens.

I tried my M4 edge to shave arm hair. Though it hooks up on my thumb nail the only part that would shave was near the choil.
I could see slight refection along the length of the edge except where it was shaving sharp. Almost no dings; just the ever so slight change in reflection width in places.

I don't doubt it will reflect and shave but I didn't get that result yet. My dark back ground was the inside of a black sintho. fleece sweater.

I should clarify that I'm not talking about a bright flashy edge, like dings and flat edges show, just a dull reflected, very thin but well defined line.
I was noting the big difference in bright flashy surface, compared to what I describe above, the other day, and thought this might be what's causing the confusion.