Chopping boards and Self-Improved Sharpness phenomenon

wootzblade

wootzblade

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We need help of the collective mind of the forum.
Researching effect of chopping boards on edge longevity, we came across the phenomenon of improved sharpness as we sliced edge-friendly chopping boards http://knifegrinders.com.au/SET/Chopping_Boards.pdf

To see if it was something about the factory edge, I re-sharpened the knife used in our chopping board experiment at the same 16 dps, using our sharpening and deburring procedure for mainstream stainless steel knives. The edge angle was controlled with our computer software for Tormek, and verified with a laser protractor.
The only difference was that I started on #80 CBN wheel to remove the metal affected by factory sharpening, and then followed our standard procedure on CBN wheels #200, #400, #1000 and deburred as described on our website http://knifegrinders.com.au/06Procedures_SS.htm

The edge scored 80 BESS, so I had to bring it to the initial sharpness of the knives used in the experiment which was 120 BESS - I did it by rounding the apex by gently honing it on the rock-hard felt wheel with 1-micron diamonds on Tormek at 2.5 degree higher than the edge angle, till the edge started scoring the same as the knife in the experiment.

Then I tested the low-density polyethylene board the same way we did with the factory-sharpened knife.
If you ask me why i did not use the best edge-friendly high-density polypropylene board - I avoided extremes on purpose as I wanted to look further into the phenomenon of self-improved sharpness as such.

re-sharpened.JPG


Following are the sharpness data and chart.
We see that the re-sharpened and cleanly deburred edge also gets sharper from slicing the chopping board due to this mystical phenomenon, and sharper than the factory edge.
We see that it is not plastic specific, and not about the burr.
I am still scratching my head for a plausible explanation of this phenomenon.
Comments are welcome.

re-sharpened_data.png


chart.png
 
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Very interesting phenomenon.

My thoughts.
(1) It is still burr/wire edge removal.
(2) Plastic board cleaned smudge off from the edge.
(3) Plastic does refine the edge.
(4) It caused some micro chipping and increased the apparent sharpness, assuming that a coarse edge performs better than a polished edge on the tester.
 
miso2 said:
Very interesting phenomenon.

My thoughts.
(1) It is still burr/wire edge removal.
(2) Plastic board cleaned smudge off from the edge.
(3) Plastic does refine the edge.
(4) It caused some micro chipping and increased the apparent sharpness, assuming that a coarse edge performs better than a polished edge on the tester.
Click to expand...

The fact that the effect fully develops between 200 - 400 cuts, we may assume that #1 and #2 have role before that, and # 3 carries on.
But it is not only about plastic, as we saw somewhat similar effect on some wooden boards as well, though to a lesser degree, as detailed in the report. But true that the plastic effect is more pronounced and regular.

Can we think of an explanation for the "Plastic does refine the edge"?
It is clear that no abrasion happens when the plastic board is edge-friendly.
 
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It could be a combination of a few causes.
I see the effect at 40 cuts (though "n" is only two), such that I would not eliminate #1 and #2 just because the effect persists.

What about #4?
Does a (refined) coarse edge score better than a polished edge on the tester?
 
We took measurements in the same point on the edge through the experiments.
When the edge is coarse, ragged, chipped - the sharpness tester readings are chaotic, the more polished the edge, the more uniform are the sharpness scores on the instrument.

I would not suggest chipping happens in the Victorinox s/s steel X50CrMoV15, for sure not under the test load of 2 kg.
Neither happens the edge rolling. Thanks to the test stand, lateral forces are way less than those perpendicular to the edge, preventing the edge rolling.
Those forces straight onto the edge do not cause the apex to mushroom or we would see worsening of the sharpness scores.

Thank you for your thoughts, as it is starting clearing...
 
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I should have been a bit clearer on chipping.
What I meant by "micro-chipping" is really a putative micron scale edge chipping/deformation.
The idea is that sharp peaks (caused by the putative "micro-chipping") would penetrate the cut medium better than a sharp ridge, thereby providing smaller force for cutting and smaller score.
Electron microscopy evaluation would be required to test this idea, though......

By the way, did you change the position of the board at each cut?
 
All boards were brand-new.
We kept changing the board position every 20 cuts through all the tests, ie after 20 cuts done in the same line on the board, the edge was moved to a fresh untouched board surface to continue there, and so on.
 
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Did you allow it to smack down on the board with ea cut like most people do. Lol jk

Neat test, i imagine you remove the burr before starting so that wouldnt be it. I would think that if anything after 20 cuts on the same line the "abrasion" would be as great or greater on the sides than the apex. I bet results would be different if each cut was in a different location.
 
It might be due to something happening inside the tiny grooves in the boards that were forming during the 20 cuts.
By the end of the test the plastic boards had noticeable grooving in the tested areas. Wooden end-grain boards also had some grooving, while the long-grain almost none.
 
It can only be from some form of burnishing.

Were the cuts done as a sliding cut, or straight down chop?

Personally I have not noticed my hardwood cutting boards (cherry, maple) to improve edge quality over time. But there are several factors at work no doubt.
 
Sliding cut.
Something made the edge apex narrower and firmer as we sliced the boards. The sharpness score on this tester improves with the narrower apex and harder apex.
 
Did the glass board also develop grooves?
If not, at least the initial improvement might not be due to burnishing.
 
wootzblade said:
We see that the re-sharpened and cleanly deburred edge also gets sharper from slicing the chopping board due to this mystical phenomenon, and sharper than the factory edge.
We see that it is not plastic specific, and not about the burr.
I am still scratching my head for a plausible explanation of this phenomenon.
Comments are welcome.
Click to expand...

You might find this interesting... in particular from 3:30 to the end...

 
One of the things I like about using kitchen knife steels known to be 'softer', i.e., more ductile, is that the ductility of the steel is what makes it easier to realign if the edge rolls or burrs a little bit. This is characteristic of kitchen stainless like the Victorinox blades and others, and is what makes them responsive to minimally-abrasive tools like a smooth (polished) honing steel. In reading this thread, it wouldn't necessarily surprise me if there's a little bit of that going on, in cutting the grooves in the cutting board. In a sliding cut, as described earlier, I could see how a fine edge with a very, very thin burr (or 'wire' edge) could be moved and/or kept into line, in drawing the edge through the material.

And if the cutting board material (low-density polyethylene) is actually playing into this, I could also see how it could effectively 'clean' the apex of loose or weak remnants of burrs, further refining the apex.

Might also be a little bit of work-hardening going on as well, if the fine edge of the blade is repeatedly being rolled slightly and then 'moved' back into shape during repeated draw-cuts in the material. In that case, I'd also expect to see the sharpness eventually degrade, as the steel at the edge becomes work-hardened to the point it becomes brittle and starts to tear away from the edge, or fold over. I've noticed this with some of my ductile kitchen stainless that I've maintained over several weeks at a time with only a smooth steel. For a while, the edge can be maintained sharp, even becoming seemingly more robust & strong in doing so. But eventually, the apex becomes weak and unstable. That's when I notice the cutting becomes hit-or-miss from one cut to the next. That's my cue to take the edge back to the stones, to strip away the weakened metal and reset the edge to clean & strong steel.
 
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Microscopic photos of the apex would help with figuring this out. Like others have noted, perhaps the plastic is polishing the steel which the tester reacts positively to? You need a SEM!
 
Obsessed with Edges said:
One of the things I like about using kitchen knife steels known to be 'softer', i.e., more ductile, is that the ductility of the steel is what makes it easier to realign if the edge rolls or burrs a little bit. . . . In a sliding cut, as described earlier, I could see how a fine edge with a very, very thin burr (or 'wire' edge) could be moved and/or kept into line, in drawing the edge through the material.
Click to expand...

Even with the hard kitchen knives perhaps.
My Little Monster for example.
LINK > > >
older thread LINK > > >
The little guy stayed hair whittling for a year of careful daily use on fruit, vegetables and opening packages.
Stayed shave sharp another six months plus !

Hahaha I then resharpened it and encouraged my partner known here as The Chef to use it when she felt like it . . . with in a week or two the edge was rounded and we had edge problems.

She has a habit of slicing something and then raking the slices off the board with the edge down against the board. I meticulously turn the knife over and rake with the spine of the knife on the board.

That might be the dif.
I resharpened.
Tactfully said maybe that wasn't a good idea to make that knife a "group use" knife.
No more edge rolling.

The knife is ONLY used on the type of cutting board you describe; softish plastic. :thumbsup: Hell I even bought one to use at work.
 
wootzblade said:
I did it by rounding the apex
Click to expand...
Sorry
I have to say : Cringe.
I'm a flat facet off the stones guy (no roundy roundy please).
Oh sure round the transition cornice behind the edge but keep the sharpening bevel geometry "pure" OFF A STONE. ;)

PS: Oops . . . that wasn't as specific as I had intended.
Pure off a sharpening jig guided stone including deburing and "stropping" on the stones.
 
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Perhaps the board material is (microscopically) splitting ahead of the knife, like a watermelon rind tends to do. If the contact is therefore less on the apex itself rather than the sides of the bevel right behind the apex this could produce a keener edge via burnishing.
 
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