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Overheated edge BESS scores
#1
Last week I assessed in-house sharpening methods at a meat factory, and found out you can tell by BESS scores if the edge has lost its temper from overheating during sharpening.

These 2 knives are identical, one sharpened by me and another by the Customer; have been cutting non-stop for 5 hours, and boned 200 pig legs each.
Can you tell by the diagram below, which knife was sharpened wrong? BESS scores are on the vertical axis.

[Image: overheated_edge.png]
http://knifeGrinders.com.au
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#2
Interesting.  Why do you think the sharpness level of the two blades converge over time?  Would it be reasonable to hypothesize that even though one edge has lost its temper, both end up rolling the same amount?  Could this indicate the depth of the loss of hardness and/or the blade just gets thick enough away from the edge to withstand the stress load in that particular environment?

Also interesting is that for the first 1.5 hrs. there is little difference in performance between the two blades.  There is only for about a 1.5 hr period where the one pig deconstructing employee has to suffer applying 0g-100g more force to demolish the pig than the other.  

By lunch time, the workload of both swine demolition technicians is basically the same.
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#3
The red was sharpened by you and blue by the customer?

Where is their cutoff for what they consider dull?
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#4
KG, thanks for this interesting quiz. Smile 

I am missing the initial sharpness of the red knife, but despite this fact I think you have sharpened the blue knife.

Jan


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#5
The initial sharpness was almost the same.

@grepper: "Could this indicate the depth of the loss of hardness ..."

That's what I think as well, just the very edge apex gets softened. The difference evens as the apex in Knife Grinders’ knives (the reddish line) gets blunt by the 3rd hour.
Checking the edges at 1.5 hour, the overheated edge is rolled, while the KG's not.

These two curves tell us more than that, and what they tell is typical, as they are average numbers drawn from many knives over several days.
Good brand knives lose the initial sharpness within the first hour of use, and stay the same pretty sharp for the next 3-4 hours - as in the diagram above, hardness 56-58 HRC; while in the inferior brands (hardness <= 55 HRC) sharpness keeps worsening with time.
In other words, change in BESS scores with work hours helps differentiate better blade steel from inferior.

@Me2 "Where is their cutoff for what they consider dull?"
When they start feeling it dull, the edge often scores in the "very sharp" range on BESS.

Someone said that the edge retention also depends on how we cut.

I was amazed  bedazed at how long the meat plant operators can maintain their knife sharp, they may have their knife shaving sharp for hours, having de-boned hundreds of legs and shoulders, cutting through tendons, not flesh.
Honestly, it's a mystique to us unsophisticated.

To be more correct, it's both art of cutting and art of steeling.
The best of them steel the edge very gently, like tongueing an oyster, one touch per side.
http://knifeGrinders.com.au
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#6
Do you know the sharpening angle and grit for each knife?
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#7
KG, than you very much for your detailed explanation of this very interesting study! Smile 

I am wondering how it is possible that your customer is able to sharpen an edge to a BESS score less than 50. Is it your apprentice?

Jan


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#8
(01-05-2018, 05:22 AM)me2 Wrote: Do you know the sharpening angle and grit for each knife?

They are identical in both groups, how else could we compare?
I had to buy a #400 CBN wheel to match the grit of the customer; our edge angle was set with computer software to match their angle of 40 degrees.

@Jan
Jan, I thought we are the best in Sydney till I met their sharpener; to start with, he sharpens almost all knives at about 100 BESS.
But when I asked him to sharpen to his best, and he spent a minute per knife instead of the usual 20-30 sec, the 4 knives we tested scored 40-50.
Can you beat it? I can't, at least not at this speed.

But I see what you mean - it's a glitchy Microsoft diagram building soft that shows initial sharpness under 50, in fact it averages around 100.
http://knifeGrinders.com.au
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#9
KG, thanks for your additional explanations. It's a remarkable real life story. Exclamation Smile

You are correct, standard MS diagram would be more useful for education purposes.

Jan


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#10
Mr, KG - I’d love to see more data if you have it and can share any of it. 
 
Real-world use is the best edge retention testing method, especially with a large sample base over an extended period and there is little of that type of testing that I have seen.   A meat factory is a rare and unique opportunity!  Your effort is commendable, and thanks for sharing.  Um, Mr. Grocer, where does bacon come from?
 
It is one thing to measure edge retention with a quick test or cutting some rope, etc., but nothing beats understanding how an edge holds up in the environment that it is used in.  From what you say, apparently you were able to measure various brands of knives with different types of steel used by a variety of tendon cutting associates.  I’m sure that provides a very well rounded overall data set to study, and I would be interested in hearing what you think after you have analyzed the data.
 
I found this interesting, “Good brand knives lose the initial sharpness within the first hour of use, and stay the same pretty sharp for the next 3-4 hours - as in the diagram above, hardness 56-58; while in the inferior brands (hardness <= 55) sharpness keeps worsening with time.
 
Cool stuff!
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