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Sharpness vs Cutting Ability
#1
New article on the definitions of sharpness and cutting ability, where I answer such questions as:

How is sharpness defined in the scientific literature?
Is sharpness better measured with its cutting behavior or by observing the edge?
Is a thinner edge automatically sharper than a thicker edge?

https://knifesteelnerds.com/2018/08/06/sharpness-vs-cutting-ability/
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#2
Well worth a few minutes of everyone's time to read. A well researched and documented article Larrin. Thank you for sharing it here.
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#3
(08-06-2018, 04:38 PM)EOU Wrote: Well worth a few minutes of everyone's time to read. A well researched and documented article Larrin.
Thanks!
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#4
Larrin, thanks for sharing your quite extensive article about sharpness and cutting ability. Smile 

If I understand you correctly, you prefer the sharpness definition based on energy necessary to initiate a cut of a test medium as it is embodied in the Blade Sharpness Index (BSI) definition.

The smallest razor blade apex radius considered in the original papers by McCarthy et al. 2007 and 2010 is 1 micron. The corresponding BSI index is some 0.2.

In the BESS approach we are considering that DE razor blade apex radius of 0.05 microns corresponds to BESS score 50 gf.

I am wondering what is the reason for such a large difference in the apex dimensions considered in the BSI and BESS approaches.
 
Jan


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#5
Those were the edges tested in the paper, not a defined limit. What is the reference for the 0.05 micron radius?
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#6
Hi Larrin,

0.05 micron is the apex radius of a standard DE safety razor, the PT50 displays it in nm, i.e. 50 nm.
The BESS-certified test line is calibrated so that 50 grams (gram-force) required to sever it with a DE razor correspond to the 50nm cutting edge apex radius. Thanks to that we can read the apex radius in nm straight from the instrument display. The display reading of 50nm tells us of the edge thickness of 100nm (50nm x 2) or 0.1 micron.

BESS Score to Edge Width correlation in the lower BESS scale
http://www.bessex.com/forum/showthread.php?tid=186

Sharpness Chart
http://www.bessex.com/forum/showthread.php?tid=205

Larrin, your side-finding in that study is dazing: "Interestingly, double bevel edges cut with less force at the same angle as the single bevel edges." - and is an interesting scientific data on the difference between the Japanese and European knife tradition.
Keeping in mind what you've found , I re-checked the edge rolling numbers for chisel grind vs double bevel blades, scattered in the EDGE RETENTION/ROLLING PART II thread, and see that in Mike's tests chisel ground bevels roll more, in support to your findings.
http://knifeGrinders.com.au
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#7
For the forumers interested in the BSI sharpness definition I am attaching the original paper referenced in Larrin’s article. The BSI (Blade Sharpness Index) paper is worth of reading provided you can digest the formulas.

BSI sharpness is calculated from energy (work) necessary to initiate a cut of a test medium. To get this energy we need to integrate (sum up) all elementary products force times displacement along the cut initiation path.

Jan


Attached Files
.pdf   On_the_sharpness_of_straight_edge_blades_PART I.pdf (Size: 1.18 MB / Downloads: 9)


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#8
(08-07-2018, 04:17 PM)Larrin Wrote: a) Those were the edges tested in the paper, not a defined limit.
b) What is the reference for the 0.05 micron radius?

ad a)
You are correct, but McCarthy et al. (2010) says: "The experiments revealed that a sharp blade (i.e. a virgin surgical scalpel blade) had a BSI of approximately 0.2 while a blunt blade (i.e. an artificially blunted blade was used) had a BSI of approximately 0.5. These values gave an indication of the upper and lower bounds for both sharp and blunt BSI values, respectively".
Based on this quote I would expect that BESS score 50 gf corresponds to BSI index of some 0.2.

ad b)
As far as I know only the EOU support document entitled: Additional Information That may be Relevant and Helpful to the Advanced Sharpener and Edge Tester.

Jan


Attached Files
.pdf   EOU_Support_Document.pdf (Size: 757.36 KB / Downloads: 3)


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#9
(08-07-2018, 05:00 PM)KnifeGrinders Wrote: Hi Larrin,

0.05 micron is the apex radius of a standard DE safety razor, the PT50 displays it in nm, i.e. 50 nm.
The BESS-certified test line is calibrated so that 50 grams (gram-force) required to sever it with a DE razor correspond to the 50nm cutting edge apex radius. Thanks to that we can read the apex radius in nm straight from the instrument display. The display reading of 50nm tells us of the edge thickness of 100nm (50nm x 2) or 0.1 micron.

BESS Score to Edge Width correlation in the lower BESS scale
http://www.bessex.com/forum/showthread.php?tid=186

Sharpness Chart
http://www.bessex.com/forum/showthread.php?tid=205

Larrin, your side-finding in that study is dazing: "Interestingly, double bevel edges cut with less force at the same angle as the single bevel edges." - and is an interesting scientific data on the difference between the Japanese and European knife tradition.
Keeping in mind what you've found , I re-checked the edge rolling numbers for chisel grind vs double bevel blades, scattered in the EDGE RETENTION/ROLLING PART II thread, and see that in Mike's tests chisel ground bevels roll more, in support to your findings.
Thanks for the links, that Science of Sharp blog is a fun one. There haven’t been that many SEM studies of finely sharpened edges.

As for the single bevel vs double bevel, I was reporting some else’s study as I indicated with the references but I agree it is very interesting. I’ve always heard that single bevel is better.
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#10
A hypothetical infinitely sharp blade is 0 on the BSI scale, and I assume that would be 0 BESS as well. I’m not sure how the BESS score would correlate exactly above 0.
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