# Maximizing Edge Retention  What CATRA Reveals about the Optimum Edge



## Larrin (Jun 18, 2018)

New article on a never-before-published CATRA study which looked at an impressive number of variables, including edge angle, edge thickness, cryo, powder metallurgy, hardness, and sharpening grit, all with 154CM and CPM-154. What makes an edge cut the longest?

http://knifesteelnerds.com/2018/06/18/maximizing-edge-retention/


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## Xenif (Jun 18, 2018)

Wow what a great article! Every one of your articles has been excellent, but this one is my favourite


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## K813zra (Jun 18, 2018)

Nice write up but I am going to have to re-read it after work. Too much for my brain over coffee.


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## Interapid101 (Jun 18, 2018)

Another great article. I'm surprised about the effect (or lack thereof) of sharpening angle. Maybe I missed it/misunderstood in the article, but any comment on how the 20 and 34 degree angles produced alternating cut lengths (ie long, short, long) from cut to cut after they lost about 50% of cut length? Wouldn't one expect that there would be a steady decline? It appears almost like the shorter cuts are stropping the edge to produce a longer cut on the next attempt.


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## Larrin (Jun 18, 2018)

Interapid101 said:


> Another great article. I'm surprised about the effect (or lack thereof) of sharpening angle. Maybe I missed it/misunderstood in the article, but any comment on how the 20 and 34 degree angles produced alternating cut lengths (ie long, short, long) from cut to cut after they lost about 50% of cut length? Wouldn't one expect that there would be a steady decline? It appears almost like the shorter cuts are stropping the edge to produce a longer cut on the next attempt.


I don't know the answer to that. I know if you watch the test you see that the cuts are not always continuous due to resetting the card stack. Perhaps that has something to do with it. I'm not sure what you mean by the lack of effect of sharpening angle since that was the strongest effect described in the article.


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## Interapid101 (Jun 18, 2018)

Larrin said:


> I don't know the answer to that. I know if you watch the test you see that the cuts are not always continuous due to resetting the card stack. Perhaps that has something to do with it. I'm not sure what you mean by the lack of effect of sharpening angle since that was the strongest effect described in the article.



Regarding sharpening angle, sorry I wasn't clear. I was referring to the notion that a more obtuse angle will retain the edge better than an acute one. In these experimental conditions, this was not the case, and the acute edge still offered a slight advantage after 60 cuts.


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## Larrin (Jun 18, 2018)

Interapid101 said:


> Regarding sharpening angle, sorry I wasn't clear. I was referring to the notion that a more obtuse angle will retain the edge better than an acute one. In these experimental conditions, this was not the case, and the acute edge still offered a slight advantage after 60 cuts.


Got it.


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## Benuser (Jun 18, 2018)

And this only makes sense with steels that easily take and hold those acute angles. And perhaps I may suggest that in normal kitchen work the board contact is a more decisive factor in edge retention than the produce. 
Thanks a lot for sharing!


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## Larrin (Jun 18, 2018)

Benuser said:


> And this only makes sense with steels that easily take and hold those acute angles. And perhaps I may suggest that in normal kitchen work the board contact is a more decisive factor in edge retention than the produce.
> Thanks a lot for sharing!


As you may know, the property of a steel to be able to handle acute edges is called "edge stability." I think it is better to evaluate it independently when it comes to comparing the behavior of the edge. Because different users, different knives, different types of cutting, and different materials being cut will lead to different "composite behavior" when combining resistance to rolling, chipping, and wear. The CATRA test focuses almost entirely on wear.


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## Benuser (Jun 18, 2018)

IIRC Wüsthof has used CATRA results in advertising. But wear resistance isn't all that relevant in the kitchen, or am I missing something?


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## Larrin (Jun 18, 2018)

Benuser said:


> IIRC Wüsthof has used CATRA results in advertising. But wear resistance isn't all that relevant in the kitchen, or am I missing something?


That depends. Are your edges blunting due to rolling, chipping, corrosion, or wear?


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## Nemo (Jun 18, 2018)

Larrin said:


> That depends. Are your edges blunting due to rolling, chipping, corrosion, or wear?


Apart from rolling, is there any way to know which each of these contributes (short of electron micrography)?


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## Larrin (Jun 18, 2018)

You would probably be able to see chipping, rolling, or corrosion with a handheld microscope.


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## Nemo (Jun 18, 2018)

Larrin said:


> You would probably be able to see chipping, rolling, or corrosion with a handheld microscope.


Mmm... Might have to get one....


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## Nemo (Jun 18, 2018)

Does this mean that for maximum edge retention (at least against silica impregnated card), a blade should be sharpened to the most acute angle that it will tolerate without generating carbide pull-out (or edge rolling for a softer knife)? Or do we not have enough information about that from this experiment?


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## Larrin (Jun 18, 2018)

Nemo said:


> Does this mean that for maximum edge retention (at least against silica impregnated card), a blade should be sharpened to the most acute angle that it will tolerate without generating carbide pull-out (or edge rolling for a softer knife)? Or do we not have enough information about that from this experiment?


Yes, the edge should be as acute as possible while avoiding chipping and/or rolling.


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## Benuser (Jun 18, 2018)

Larrin said:


> That depends. Are your edges blunting due to rolling, chipping, corrosion, or wear?



Probably by micro-corrosion and wear due to board contact, and for the wear not so much by the cutting itself.


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## HRC_64 (Jun 18, 2018)

That raises an intersting question,
how does acid + wear resistance
play out in the real world?

154 variants are already some 
degree of stainless,

but maybe in general does
high wear rating help
vs acids ?

Or, are the two variables
not usefully correlated?


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## Larrin (Jun 18, 2018)

The only thing that helps against corrosion is corrosion resistance. There is some literature out there on combined corrosion and wear but Im not sure if there are any on blades.


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## HRC_64 (Jun 18, 2018)

Makes sense, 
thanks for the explanation.


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## LifeByA1000Cuts (Jun 18, 2018)

Wouldn't BESS style measurements taken after testing repeated *impact* on wood layered with some substance of edible texture be far more relevant than cardboard cutting....?


...


How long does the edge on the cheapest kind of yanagiba (420J2 steel) last, once decently sharpened? ... Longer than one would think, if only used as a strict pull cutter....


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## HRC_64 (Jun 18, 2018)

For people who are just skimming the thread, this pic is from the article.
Very well done writeup, so encourage people to click thru,

>http://knifesteelnerds.com/2018/06/18/maximizing-edge-retention/


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## Dave Martell (Jun 18, 2018)

Another nice article Larrin.


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## carlBC (Jun 18, 2018)

Wow this was a really interesting article. THanks for the read. Learned a lot and well presented. Will inform my future purchases/sharpening!


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## panda (Jun 18, 2018)

can someone give me the cliff notes version (laymans summary)?


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## carlBC (Jun 18, 2018)

panda said:


> can someone give me the cliff notes version (laymans summary)?



I'm a knife scrub but decent with data usually, so either this is highly appropriate or highly inappropriate to answer 

The shallower the angle of the knife tested until 20 degrees (10 a side) on the type of steel they used correlated very strongly with ability to cut better over time.

However the biggest drop in cutting ability happens very quickly and similarly across knives, the original advantage of the 20 degree knife is eroded over time, but stays sharper longer.

Hardness, edge thickness, hardening technique (cyro, yes or no), and grit of final stone used all correlated with edge retention SLIGHTLY, no where near the magnitude of the angel sharpened too.

EDIT: Cliff of CLiff: So sharpen your knives well to the finest edge you can wo rolling/damaging profile of the edge (im assuming this is some sort of given, sharpen well...). It will cut better longer, this was tested between 20 and 60 degrees


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## panda (Jun 18, 2018)

so this scientifically just confirmed what we already knew?


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## carlBC (Jun 18, 2018)

panda said:


> so this scientifically just confirmed what we already knew?



With a very large degree of magnitude lus1:

That said I actually didn't know this, I had heard a bunch of myth about thicker edge maybe lasting longer. And it puts a contrast on HOW correlated it is. This correlation dwarfs all others listed.

So buying a high HRC blade is good because you CAN sharpen it to a finer edge. Just having a harder blade won't make the edge last longer (well it will, but this improvement is absolutely dwarfed by edge angle) - so if you don't want to sharpen or can't better than, 40 degrees for whatever reason theres no purpose to a higher HRC blade


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## labor of love (Jun 18, 2018)

Sounds like a guideline for those who favor edge stability. But for those that favor edge retention...well thats another can of beans...no? I probably shouldnt even comment yet as I havent read the actual article.


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## carlBC (Jun 18, 2018)

labor of love said:


> Sounds like a guideline for those who favor edge stability. But for those that favor edge retention...well thats another can of beans...no? I probably shouldnt even comment yet as I havent read the actual article.



The data looked like it showed that over more cute the lower angled knives always cut better than the knife on a similar number of cuts sharpened to a different angle. Initial advantage is never overcome by some other property...but I also would really like to know if I am misreading this horribly wrong, as, again, scrub

"There was a difference in final thickness of the apex of the edge after the knives were run through the CATRA test. The 20° edge was about 23 microns after the test, 34 degrees led to about 19-20 microns, and the 50° were around 16-17 microns. All of these images are of the ingot 154CM steel. So it appears that with a lower angle edge it can wear down to a larger apex and still maintain better sharpness than a higher angle edge."


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## HRC_64 (Jun 18, 2018)

My question is, which one will (best) cut a tomato after the test? 

The thin edge which lost more apex but still benefitted from geometry;
or the thick edge which kept more apex, but was hobbled by its geometry.

(note the test substrate was a hard product, not that there's anything wrong with that)


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## Barmoley (Jun 19, 2018)

Great article, you guys should read it. Larrin mentioned that this test is mostly a test of wear resistance which makes sense since the machine cuts in a certain way and it is cutting abrasive material. So the study is very useful in predicting cutting ability and to show that for the same/similar steel angle is the most significant variable in predicting how long the edge will last. You cant blindly say that more acute angles are always better once different steels are involved, it might be, but this study wasnt about that, hopefully future studies. If the steel can support very acute angles then sure, but if the knife dulls due to chipping, rolling or eroding then more abtuse angle might last longer. So a perfect steel would need to be very tough, get very hard, be very stain resistant and very wear resistant. Fortunately such blade material doesnt exist because if it did this hobby would be over :bigeek:


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## madelinez (Jun 19, 2018)

I'm surprised how little a difference the PM process makes. Would be interesting to see a similar study on toughness.


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## Larrin (Jun 19, 2018)

madelinez said:


> I'm surprised how little a difference the PM process makes. Would be interesting to see a similar study on toughness.


There is a comparison between an ingot and PM steel here: https://knifesteelnerds.com/2018/06/04/toughness-testing-cru-wear-z-wear/


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## Larrin (Jun 19, 2018)

panda said:


> so this scientifically just confirmed what we already knew?


On some other forums they are arguing about how they still know what they know despite this study.


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## Nemo (Jun 19, 2018)

panda said:


> so this scientifically just confirmed what we already knew?


This issue is at the heart of what constitutes the scientific process.

One starts with a hypothesis and attempts to disprove it with an experiment.


Essentially, unless you have experimental evidence for it, it's only an educated guess or an opinion, not knowledge.


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## rick alen (Jun 19, 2018)

I don't understand why the DMT 8K leaves such deep gouges, let alone the jagged edge. I know people have said it sharpens like a 3K when new and even after lengthy break-in it is still no better than 6K. But why would a 600 be so comparatively smooth?


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## Dave Martell (Jun 19, 2018)

rick alen said:


> I don't understand why the DMT 8K leaves such deep gouges, let alone the jagged edge. I know people have said it sharpens like a 3K when new and even after lengthy break-in it is still no better than 6K. But why would a 600 be so comparatively smooth?




The abrasive particles are shaped differently.


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## Knifefan (Jun 19, 2018)

Does anyone have an idea how the CATRA test actually relates to real-life use, like 1 stroke on the CATRA machine equals to 1 week use in an average home kitchen?


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## Knifefan (Jun 19, 2018)

Great article, btw.


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## Xenif (Jun 19, 2018)

Knifefan said:


> Does anyone have an idea how the CATRA test actually relates to real-life use, like 1 stroke on the CATRA machine equals to 1 week use in an average home kitchen?


That will be very hard to compare as we all have diffrent knife strokes, cutting boards, produce to cut, etc.


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## milkbaby (Jun 19, 2018)

Knifefan said:


> Does anyone have an idea how the CATRA test actually relates to real-life use, like 1 stroke on the CATRA machine equals to 1 week use in an average home kitchen?



I don't think there is a simple correlation. The CATRA test is slicing through cardstock impregnated with abrasive. Slicing through a tough substrate (like cutting rope or cardboard) seems to be the typical test protocol for measuring what's called "edge retention". But there's also edge stability issues in the kitchen as an edge rolls or fractures irregularly, I think. So it's possible edge dulling/wear will come from a different combination/ratio of factors in the kitchen, it seems like most wear will be from board contact and for carbon steel knives maybe corrosion? But this is just conjecture on my part.


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## Barmoley (Jun 19, 2018)

This CARTA test would be great at predicting performance of a mandeline and similar kitchen tools. Are "blades" on mandeline single bevel, as it seems that the lowest angle the steel can support would be the way to go to maximize how long the edge would last.


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## Larrin (Jun 19, 2018)

CATRA reports that "consumer panels" that rated knives based on edge retention correlated highly with edge retention results other than for textile cutting. Phil Wilson reports that his rope cutting correlates well with CATRA. I don't have any specific data on kitchen use.


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## rick alen (Jun 19, 2018)

Dave Martell said:


> The abrasive particles are shaped differently.




So the 600 has particles like flat disks that shave material (there are actually relatively large particle abrasives shaped like this for polishing some copper alloys) and the 8K like spades? I would think it would have to be at least that radical a difference.


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## Keith Sinclair (Jun 19, 2018)

Thanks for the article. Interesting that it reinforces much of what many here already know from experience. Grind is very important and higher grit stones don't improve cutting with gyuto's doing massive prep. A medium stone cut the most cards.


How knives cut tomatoes. Thin edges rule in my experience sharpened on a 1K stone. Have cut as many as two 25# cases of tomatoes for Lomi Salmon at once. Wash & use a tomato corer to take out stem. Slice and dice. Dicing 50# of tomatoes with a carbon gyuto would only use a polishing steel just a couple lite measured strokes a few times because of the edge repeat hitting on a plastic board. No way I could do that with a stainless Forschner.

Know I sound like a broken record but most persons saying acidic foods dull carbon knives have little or no experience cutting massive amounts of acidic foods to back up their statements.


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## Barmoley (Jun 19, 2018)

Acidic foods must dull carbon knives and even stainless knives, the question is how fast. Might not matter if it happens slowly enough. Maybe another study, after comparing different steels on the CARTA test.


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## Keith Sinclair (Jun 19, 2018)

How did all that acidic food get cut before stainless was invented early 20th century? Any knife dulls no matter what steel it is. I first read about acidic foods dulling carbon in a Chad Ward book. Have read it often on knife forums. Acidic foods will quickly stain a new carbon blade, if a blade is not being used laying around it will corrode. A carbon blade if it is touched up on the stone is capable of cutting acidic foods all day long.


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## panda (Jun 19, 2018)

keith the whole dont cut acidic foods with carbon is just one of those home cook myths..


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## merlijny2k (Jun 20, 2018)

Keith Sinclair said:


> How did all that acidic food get cut before stainless was invented early 20th century? Any knife dulls no matter what steel it is. I first read about acidic foods dulling carbon in a Chad Ward book. Have read it often on knife forums. Acidic foods will quickly stain a new carbon blade, if a blade is not being used laying around it will corrode. A carbon blade if it is touched up on the stone is capable of cutting acidic foods all day long.



If it is from Ward treat with great caution. 

In any case my Blue steel gyuto keeps cutting tomato's much, much longer without sharpening than euro stainless. It is just that the rod takes 5 seconds and the stone takes 5 minutes and the result for sharpening as far as tomatoes are concerned are similar. Therefore usually I reach for the softsteel anyway. But never noticed anything about my carbons suffering from pineapple or something. It may stink quite a bit if the patina is young but it stays sharp.

I agree though that a tomato should be part of the evaluation at some point because tomatoes and peppers are the only thing that makes you want to sharpen anyway. For most other work a non abused hardsteel edge lasts practically forever. At least in my home, while tomato ability starts to drop after 1 or 2 meal preps for my softsteel knives or 5 to 10 meals for the J-knife. 10 out of 10 times my wife asks me to sharpen her knife it is also from tomato struggles.


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## Benuser (Jun 20, 2018)

A few very light strokes on a dry fine stone and your Blue Steel edge is restored.


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## K813zra (Jun 20, 2018)

panda said:


> keith the whole dont cut acidic foods with carbon is just one of those home cook myths..



Funny you should say that because I had never heard of it until I started using these forums. Regardless, I use carbon on tomatoes just and I can a lot of them even if only once a year.  (Limited use on lemons/limes etc.)


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## merlijny2k (Jun 20, 2018)

Benuser said:


> A few very light strokes on a dry fine stone and your Blue Steel edge is restored.



I'll try that what do you recommend Eden 5k or Coti?


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## Benuser (Jun 20, 2018)

merlijny2k said:


> I'll try that what do you recommend Eden 5k or Coti?



Don't know the Eden. I use the Snow-white Naniwa Junpaku 8k. Coticule will work as well.


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## nopomo (Jun 20, 2018)

Keith Sinclair said:


> A carbon blade *if it is touched up on the stone* is capable of cutting acidic foods all day long.



Not that I disagree, but is that meaningful? Any knife will cut anything for any duration if you sharpen it whenever it dulls.


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## Benuser (Jun 20, 2018)

nopomo said:


> Not that I disagree, but is that meaningful? Any knife will cut anything for any duration if you sharpen it whenever it dulls.



Meant here is a touching up consisting of a few strokes, hardly a sharpening. The question is whether this is particular to carbons, or not. Stainless edges, especially if not highly polished, will suffer from dulling as well if not cleaned in time after contact with acidic food.


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## HRC_64 (Jun 20, 2018)

keep in mind often the issue with tomatoes is "teeth", 
not sharpness in some absolute sense.

so benuser is saying you can put some "bite" 
back in the edge with minor work.


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## HRC_64 (Jun 20, 2018)

my earlier comment upthread about tomoatoes was along similar lines,
the catra test showed significanly more 
deformation on the apex of the acute apex.

that means perhaps a dis-proportionately
impact on edge polish/toothiness, etc
even if superior geometry remains

it would be interesting (even if academic)
to consider if the "Worse edge" had
ability to remain toothy longer...


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## Barmoley (Jun 20, 2018)

I think what Larrin is doing and studies like these are interesting and useful. They help us understand what is going on with edges in controlled cutting environment and show which of the attributes affect performance more than others. How this translates to use in kitchen knives is more difficult to answer, since too many variables are involved. I don't think anyone was implying you can't use carbon knives for acidic foods or anything else, ofcourse you can, as humans have done for thousands of years. The article also didn't make any conclusion of which steel is better for anything.


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## Keith Sinclair (Jun 20, 2018)

HRC_64 said:


> keep in mind often the issue with tomatoes is "teeth",
> not sharpness in some absolute sense.
> 
> so benuser is saying you can put some "bite"
> back in the edge with minor work.



A toothy edge works on a majority of food. Most cooks in the real world sharpen on one medium stone. Certainly Japanese single bevels are different. The geometry of a SB with a hollow ground backside make for some of the finest edges finished on a polishing stone.


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## LifeByA1000Cuts (Jun 21, 2018)

I have had carbon edges notably degrade through a handful of tomatoes... as in, would easily bite the first and would be erratic on the fifth... sure it is a myth? Or is there reason to believe the tomato skin is just so damn tough it works as an anti-strop?


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## Barmoley (Jun 21, 2018)

I've had similar happen. I suspect 2 possibilities, either there was a burr/wire edge or the edge was too polished. For me my edges seem to last longer on tomatoes with lower grid. I used to do 6000 and 4000 feels sharper longer. My plan is to try 2K and 1K next or even DMT 600:bigeek:


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## HRC_64 (Jun 21, 2018)

In one of salty's videos he talks about moving his edgeto keep it (razor) sharp...on a single tomato...


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## madelinez (Jun 21, 2018)

LifeByA1000Cuts said:


> I have had carbon edges notably degrade through a handful of tomatoes... as in, would easily bite the first and would be erratic on the fifth... sure it is a myth? Or is there reason to believe the tomato skin is just so damn tough it works as an anti-strop?



I go through a lot of tomatoes (and pickles) with my carbon steel knives and they stay peak sharpness for a month or two at least. Sounds more like you're experiencing a wire edge.


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## K813zra (Jun 21, 2018)

My FKH (SK-4 @ 58 HRC) lasts through the entire canning season without touching anything more than a stack of slack newsprint and I don't squash my tomatoes. Then again, I am not trying to chop them either. Push/pull/slice is fine by me. No need, for me, to rapid chop a bushel of tomatoes. (Edge is that left from an Ikarashi fwiw.)


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## bahamaroot (Jun 22, 2018)

LifeByA1000Cuts said:


> I have had carbon edges notably degrade through a handful of tomatoes... as in, would easily bite the first and would be erratic on the fifth... sure it is a myth? Or is there reason to believe the tomato skin is just so damn tough it works as an anti-strop?


Tomatoes have plenty of acid that degrades a knife edge rather rapidly compared to other veggies. I can tomatoes every year and you can definitely notice degradation in a knife edge after several tomatoes. That's not to say the knife is immediately dull but the degradation is definitely noticeable. The acid in tomatoes will definitely kill that fresh off the stone edge as fast as anything you will cut.


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## bahamaroot (Jun 22, 2018)

K813zra said:


> *My FKH (SK-4 @ 58 HRC) lasts through the entire canning season without touching anything more than a stack of slack newsprint* and I don't squash my tomatoes. Then again, I am not trying to chop them either. Push/pull/slice is fine by me. No need, for me, to rapid chop a bushel of tomatoes. (Edge is that left from an Ikarashi fwiw.)


Not with a 58Hrc knife or your not canning that much, especially tomatoes.


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## K813zra (Jun 22, 2018)

bahamaroot said:


> Not with a 58Hrc knife or your not canning that much, especially tomatoes.



I sure do, every year. About A basket every few days for a couple of weeks.


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## bahamaroot (Jun 22, 2018)

Total BS.


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## K813zra (Jun 22, 2018)

bahamaroot said:


> Total BS.



Whatever you say.


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## HRC_64 (Jun 22, 2018)

K813zra said:


> Whatever you say. ...



How can you resist the urge to sharpen _anything_ for that long :rofl:


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## K813zra (Jun 22, 2018)

HRC_64 said:


> How can you resist the urge to sharpen _anything_ for that long :rofl:



Not as long as you might think. I grow two to three tomato plants and two cucumbers. I don't grow a forest. And I have stone tester knives for daily sharpening. (Tojiro ITK and Zakuri B#1)


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## bahamaroot (Jun 22, 2018)

If that's all you grow then you don't can that much. I've got 14 tomato plants alone. Those "baskets" you speak of must be pretty small. I'm talking about doing several cases of Juice quarts and another several cases of diced tomato quarts on top of what we use fresh. I can enough tomatoes to last us through the rest of the year and have plenty to give to family and neighbors.


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## HRC_64 (Jun 22, 2018)

yeah, even our season is like 4-6weeks and its not california
or somewhere with proper mediterranean climate


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## K813zra (Jun 22, 2018)

bahamaroot said:


> If that's all you grow then you don't can that much, I've got 14 tomato plants alone. Those "baskets" you speak of must be pretty small. I'm talking about doing several cases of Juice quarts and another several cases of diced tomato quarts on top of what we use fresh. I can enough to last us through the year and have plenty to give to family and neighbors.



Didn't mean to imply it was hundreds of cans of tomatoes just that the edge isn't going to become completely useless on tomatoes after just a few which was earlier implied. Apologies, I will try to be more exact in the future.


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## Barmoley (Jun 22, 2018)

This is a perfect demonstration of why what Larrin is doing is so useful and interesting. All the talk about real life use and cutting tomatoes for days, month years..... Precisely why scientific method and experimentation is so important. I am not doubting any of the participants and believe that all are truthful, the problem is that until you define what sharp is and what a generic tomato is, besides all the other parameters you cant compare these things.


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## Larrin (Jun 22, 2018)

It would be fun to set up an experiment with a sharpness tester and some common acidic foods. Maybe someone has even done it already.


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## Keith Sinclair (Jun 22, 2018)

Barmoley said:


> This is a perfect demonstration of why what Larrin is doing is so useful and interesting. All the talk about real life use and cutting tomatoes for days, month years..... Precisely why scientific method and experimentation is so important. I am not doubting any of the participants and believe that all are truthful, the problem is that until you define what sharp is and what a generic tomato is, besides all the other parameters you cant compare these things.



Agree, the large amounts of tomatoes I cut were not vine ripe, but my carbons could go through many slicing and dicing. When I worked in a large banquet Hotel we used a machine to dice tomatoes for lomi salmon. It was terrible the lomi came out mushy. Only a sharp knife makes good Lomi Salmon.

All I can say is cut tons of acidic foods with carbon knives over 25 years and never crossed my mind that acid was dulling them. Thin geometry and easy to sharpen carbon worked better than my stainless knives. My knives were the most borrowed for special jobs, sometimes I would come back from setting up a banquet and find a chef using my knives to clean & portion fish and meats than ran out on the front line. They would go straight to my carbons because I kept them sharp. Was a total carbon junky only later found out about user friendly powder steels like R2 and SRS15. Others ,G3 AEB-L much better than any stainless I had ever used before.


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## Paraffin (Jun 22, 2018)

Larrin said:


> It would be fun to set up an experiment with a sharpness tester and some common acidic foods. Maybe someone has even done it already.



That would be difficult to calibrate to real-world conditions, since some of us are apparently seeing quick degrading of the edge with acidic food, and others aren't. I don't cut cases of tomatoes or lemons at a time, but I have gone through a couple dozen plum tomatoes with my carbon knives when making a huge pot of tomato or chili sauce, without noticing any decline in cutting ability. 

Also, I'm having trouble imagining a reaction that would actually _remove_ or _re-shape_ metal at the blade edge in a relatively short amount of time, say an hour or two of heavy tomato prep. This isn't hydrofluoric acid we're talking about here.


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## bahamaroot (Jun 22, 2018)

Barmoley said:


> This is a perfect demonstration of why what Larrin is doing is so useful and interesting. All the talk about real life use and cutting tomatoes for days, month years..... Precisely why scientific method and experimentation is so important. I am not doubting any of the participants and believe that all are truthful, the problem is that until you define what sharp is and what a generic tomato is, besides all the other parameters you cant compare these things.


 I agree, it would take a much more scientific method to clarify any of this, too many variables at play here.
The only thing I can say for certain is if you cut a bushell or so of tomatoes you will definitely feel the degradation of any edge be it carbon or especially a soft stainless. Tomatoes are that acidic. I'm in know way saying that it will render the knife edge near useless but there will be a major difference between the starting edge and the ending edge just from the acid.


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## Nemo (Jun 22, 2018)

Paraffin said:


> Also, I'm having trouble imagining a reaction that would actually _remove_ or _re-shape_ metal at the blade edge in a relatively short amount of time, say an hour or two of heavy tomato prep. This isn't hydrofluoric acid we're talking about here.



But we are also only talking about remiving or reshaping or chemically changing a fraction of a micron of steel.


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## Nemo (Jun 22, 2018)

Larrin said:


> It would be fun to set up an experiment with a sharpness tester and some common acidic foods. Maybe someone has even done it already.


Test cuts on rope soaked in vinegar vs rope soaked in water?


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## Barmoley (Jun 22, 2018)

I don't think it is acidic food in general I think it is tomatoes specifically, especially really ripe tomatoes. When the skin is tough and there is no support. This doesn't happen with tomatoes that are not soft, those you can cut for a while without noticing edge changes. It is unlikely to be caused by acid, tomato skins are tough and the fruit is soft, so tiny edge changes are very noticeable.


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## Larrin (Jun 22, 2018)

Paraffin said:


> That would be difficult to calibrate to real-world conditions, since some of us are apparently seeing quick degrading of the edge with acidic food, and others aren't. I don't cut cases of tomatoes or lemons at a time, but I have gone through a couple dozen plum tomatoes with my carbon knives when making a huge pot of tomato or chili sauce, without noticing any decline in cutting ability.
> 
> Also, I'm having trouble imagining a reaction that would actually _remove_ or _re-shape_ metal at the blade edge in a relatively short amount of time, say an hour or two of heavy tomato prep. This isn't hydrofluoric acid we're talking about here.


Well first we should look at a relatively extreme case just to see what could realistically occur. Such as lemon juice immersion of the edge and sharpness tested after 1, 3, 10, 30, 100, 300 minutes. For example, if there was a measurable loss of sharpness after 1 minute that would confirm that corrosion affecting the edge is not only possible but relatively likely with corrosive foods. On the other hand if after 300 minutes there was no drop in sharpness that would indicate that loss of the edge through normal cutting and cleaning would be unlikely. Youd need a good sharpness tester.


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## panda (Jun 22, 2018)

those that dont believe a 58hrc knife can last through blasting away tomatoes is cause you're not that good at sharpening despite what you might think and/or your technique is the culprit (too much board contact/force)


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## Nemo (Jun 22, 2018)

Larrin said:


> Well first we should look at a relatively extreme case just to see what could realistically occur. Such as lemon juice immersion of the edge and sharpness tested after 1, 3, 10, 30, 100, 300 minutes. For example, if there was a measurable loss of sharpness after 1 minute that would confirm that corrosion affecting the edge is not only possible but relatively likely with corrosive foods. On the other hand if after 300 minutes there was no drop in sharpness that would indicate that loss of the edge through normal cutting and cleaning would be unlikely.


Good idea.

The only confounding factor I can think of is rhat there may be an interaction between the acid and the abrasion on the edge caused by cutting.


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## bahamaroot (Jun 22, 2018)

Barmoley said:


> I don't think it is acidic food in general I think it is tomatoes specifically, especially really ripe tomatoes. When the skin is tough and there is no support. This doesn't happen with tomatoes that are not soft, those you can cut for a while without noticing edge changes. It is unlikely to be caused by acid, tomato skins are tough and the fruit is soft, so tiny edge changes are very noticeable.


It's definitely the acid in the tomato. All of the tomatoes I cut when canning have already been blanched and peeled by pulling the skin off before cutting. No skin is ever cut and I cut the tomatoes in hand over a 1/2 sheet so board contact is not a problem either.


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## Larrin (Jun 22, 2018)

Nemo said:


> Good idea.
> 
> The only confounding factor I can think of is rhat there may be an interaction between the acid and the abrasion on the edge caused by cutting.


But doing both at a time would leave you unable to determine the individual effects. If acid alone didnt affect the edge a second experiment could be cutting some fixed material (such as rope as you said) both with and without the acid. But the wear from the rope may overwhelm the effect of corrosion.


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## Barmoley (Jun 22, 2018)

Larrin said:


> Well first we should look at a relatively extreme case just to see what could realistically occur. Such as lemon juice immersion of the edge and sharpness tested after 1, 3, 10, 30, 100, 300 minutes. For example, if there was a measurable loss of sharpness after 1 minute that would confirm that corrosion affecting the edge is not only possible but relatively likely with corrosive foods. On the other hand if after 300 minutes there was no drop in sharpness that would indicate that loss of the edge through normal cutting and cleaning would be unlikely. Youd need a good sharpness tester.



This would be a great test that would really show how much food corrosion affects edges. Some effect has to exist, but how severe and how rapid are very interesting questions.


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## bahamaroot (Jun 22, 2018)

panda said:


> those that dont believe a 58hrc knife can last through blasting away tomatoes is cause you're not that good at sharpening despite what you might think and/or your technique is the culprit (too much board contact/force)


Never said that I dont believe a 58hrc knife can last through blasting away tomatoes. Only that that knife will not last a whole season of canning something like tomatoes with only stropping on newspaper. After several hours of cutting up nothing but tomatoes there will be a definite difference in the edge. And it won't survive a whole SEASON with just news stropping regardless of your sharpening skills. And mine are quite good rather you believe it or not.


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## Nemo (Jun 22, 2018)

Larrin said:


> But doing both at a time would leave you unable to determine the individual effects. If acid alone didnt affect the edge a second experiment could be cutting some fixed material (such as rope as you said) both with and without the acid. But the wear from the rope may overwhelm the effect of corrosion.


Agreed. 
I guess you'd have to have 3 arms: acid only, abrasion only and acid plus abrasion in order to tease out the differences.


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## Nemo (Jun 22, 2018)

Barmoley said:


> This would be a great test that would really show how much food corrosion affects edges. Some effect has to exist, but how severe and how rapid are very interesting questions.


It would also be interesting to compare different steels.


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## Barmoley (Jun 22, 2018)

To make it simpler you could just do simple high carbon and acid like Larrin suggested. If there wasn't enough of an effect, you could reasonably infer if acid is the cause.


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## Larrin (Jun 22, 2018)

Yes it would be reasonable to start with a simple carbon steel for a baseline. Then compare with stainless, for example.


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## Paraffin (Jun 22, 2018)

Nemo said:


> Agreed.
> I guess you'd have to have 3 arms: acid only, abrasion only and acid plus abrasion in order to tease out the differences.



I'm still wearing my skeptic's hat about a purely chemical reaction from tomato acidity causing any change in cutting action over a period of a few hours. That would be a powerful change in the metal of the blade edge on a microscopic level. It would be the first thing to test, because we all sharpen differently with different amounts of "tooth" that will affect cutting veg.

So, expose the blade edge to tomato juice over a few hours and then take a series of electron micrographs at different magnifications, like those at the scienceofsharp web site. Preferably with a few different metal types. Compare that to micrographs of the blade edge before acid exposure. This would demonstrate whether acidic foods alone are a factor. 

Maybe someone can talk that guy at scienceofsharp into testing it, or a phase 2 of the OP article.


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## bahamaroot (Jun 22, 2018)

Would be simple to do a test cut with a freshly sharpened knife and then soak the knife in tomato juice and then repeat the test cut to check for comparison.

The next question would be does the combination of the acid and the cutting through the fiber of the tomato combined, even as delicate as it is, make a difference. Acid and light friction....


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## Keith Sinclair (Jun 23, 2018)

Putting a knife in a glass of lemon or tomato juice & testing it on equal tomatoes or lemons before and after would be a test. I prefer the real world where it counts that's what knives are for cutting food.

Take a case of tomatoes or lemons split it in half equal to each cutter. Slice & dice tomatoes or cut the lemons into wedges. I'll take a thin carbon laser, you take the stainless knife of your choice. If corrosion guys are right esp. a super thin edged carbon will dull in the act of cutting and quit performance. Save one lemon or tomato at end to see how each cuts. 

As said agreed with the findings of this test even though it was cutting cards. A medium grit cut over 1000 cards and knife geometry was most important factor. A toothy 1K edge is best for tomatoes, bell peppers lots of food and keeps working for hours. Polished edges do not work as well for lots of prep. unless it is sushi or sashimi.


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## HRC_64 (Jun 23, 2018)

The acid just weakens the (apex) metal a tiny amount, 
its the board contact that kills the (now weakened) edge....



ALso, with tomatoes, I swear the seeds don't help 
those seeds between your board...and the knife


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## bahamaroot (Jun 23, 2018)

My knives dull cutting tomatoes for hours and the knife never touches a board, I cut them in hand. Acid and seeds?


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## HRC_64 (Jun 23, 2018)

There is fibrous material in side the tomato, besides the seeds,
of course so this makes some sense...


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## Larrin (Jun 23, 2018)

A microscope isnt necessary if using a sensitive sharpness tester using a finely sharpened edge. Any change would show up.


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## Paraffin (Jun 23, 2018)

Larrin said:


> A microscope isnt necessary if using a sensitive sharpness tester using a finely sharpened edge. Any change would show up.



I agree that a sharpness test under controlled (and repeatable) conditions would show whether tomato acid reduces sharpness. I hope someone can do that, and put this idea to rest one way or another.

Regarding the microscope... I'm still curious about the proposed mechanism for weakening the edge. Tomatoes have a very mild level of acidity, compared to the industrial acids that we know can etch and physically change metals. An electron micrograph would show pitting or other changes that could reduce cutting ability.


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## Larrin (Jun 23, 2018)

Paraffin said:


> I agree that a sharpness test under controlled (and repeatable) conditions would show whether tomato acid reduces sharpness. I hope someone can do that, and put this idea to rest one way or another.
> 
> Regarding the microscope... I'm still curious about the proposed mechanism for weakening the edge. Tomatoes have a very mild level of acidity, compared to the industrial acids that we know can etch and physically change metals. An electron micrograph would show pitting or other changes that could reduce cutting ability.


A microscope would be great for observing how the edge was corroded for sure.
This website lists food acidity: http://www.webpal.org/SAFE/aaarecovery/2_food_storage/Processing/lacf-phs.htm

It looks like tomatoes are around 4.5 pH, though apples, oranges, and lemons are all more acidic.


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## Keith Sinclair (Jun 23, 2018)

Most seafood is high on pH level. You acid dulling knives worry dudes better go over to Tsukiji market and tell those poor dumb Japanese to stop using their carbon knives to clean all that fish right now. Get Sushi chefs to ditch their carbon Yanagiba's and Deba's and get stainless. 

If you are cutting tomatoes in your hand it's a good thing your knife is not that sharp.


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## Paraffin (Jun 23, 2018)

Larrin said:


> A microscope would be great for observing how the edge was corroded for sure.
> This website lists food acidity: http://www.webpal.org/SAFE/aaarecovery/2_food_storage/Processing/lacf-phs.htm
> 
> It looks like tomatoes are around 4.5 pH, though apples, oranges, and lemons are all more acidic.



Yeah, that's why I'm still skeptical. I've never heard anyone say that cutting apples will dull a blade more quickly than other produce, and they're more acidic than tomatoes. Not that I'm doubting anyone's personal experience, but it could be something other than a fairly mild low PH that's affecting the edge that quickly.


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## Larrin (Jun 23, 2018)

Keith Sinclair said:


> Most seafood is high on pH level. You acid dulling knives worry dudes better go over to Tsukiji market and tell those poor dumb Japanese to stop using their carbon knives to clean all that fish right now. Get Sushi chefs to ditch their carbon Yanagiba's and Deba's and get stainless.
> 
> If you are cutting tomatoes in your hand it's a good thing your knife is not that sharp.


On the list the seafood looks like its mostly close to neutral (7).


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## HRC_64 (Jun 23, 2018)

Keith Sinclair said:


> If you are cutting tomatoes in your hand it's a good thing your knife is not that sharp.



Agreed. :lol2:


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## Keith Sinclair (Jun 23, 2018)

Larrin said:


> On the list the seafood looks like its mostly close to neutral (7).



Yes your right


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## Larrin (Jun 23, 2018)

I found this: http://www.edgeonup.com/Video PT50B Oxidation LR.mp4


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## HRC_64 (Jun 23, 2018)

Larrin said:


> I found this: http://www.edgeonup.com/Video PT50B Oxidation LR.mp4



I can't really follow how the machine works 



> PT50B... This instrument is the direct replacement for our original PT50 which is currently at work throughout the US and 17 countries world-wide. With a faster processor and simpler operation the PT50B is the workhorse instrument for professional sharpeners, knife enthusiasts and woodworkers. The PT50B has a steel measurement platform and delivers 5 grams of resolution with a 1 year warranty. 5 grams of resolution is more than adequate for all the sharpening room discoveries you will soon be making! The PT50B includes a knife fulcrum and our Aluminum Test Fixture. The PT50B can easily use our Disposable Clip system if purchased separately. The clip system is not only versatile, super fast and simple but a real advantage for anyone with diminished eyesight and/or hand and finger dexterity.



some other crazy products, here...

http://edgeonup.com/Analog Testers.html


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## Larrin (Jun 23, 2018)

The machine is a scale with an aluminum block on top that holds taut a thread. You press the blade onto the thread until it cuts through. The maximum weight applied is displayed on the scale.


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## HRC_64 (Jun 24, 2018)

Ok, I was trying to understand that ... 
thanks for making it more clear.


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## bahamaroot (Jun 24, 2018)

Keith Sinclair said:


> ...If you are cutting tomatoes in your hand it's a good thing your knife is not that sharp.


Not dull knives, that much skill.


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## bahamaroot (Jun 24, 2018)

Larrin said:


> A microscope would be great for observing how the edge was corroded for sure.
> This website lists food acidity: http://www.webpal.org/SAFE/aaarecovery/2_food_storage/Processing/lacf-phs.htm
> 
> *It looks like tomatoes are around 4.5 pH, though apples, oranges, and lemons are all more acidic.*





Paraffin said:


> *Yeah, that's why I'm still skeptical. I've never heard anyone say that cutting apples will dull a blade more quickly than other produce, and they're more acidic than tomatoes.* Not that I'm doubting anyone's personal experience, but it could be something other than a fairly mild low PH that's affecting the edge that quickly.


I've never cut apples, oranges or lemons for a couple hours at a time to know how they affect edges. Only tomatoes, that's why I only mention them.
All the others may be as bad or worse but I don't have the first hand knowledge to know.


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## HRC_64 (Jun 24, 2018)

are you using a cut glove? why cut them up in hand 
if we are talking peeled tomatoes, sounds slippery


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## bahamaroot (Jun 24, 2018)

I'm dropping them directly into a canning jar through a funnel as I cut them. I used a cut glove when I first started cutting like this but haven't used one in years. I use only the slightest of a slicing motion, more just simply a light push through the tomato. It drops through very easy and it's really not that hard to get a feel for when to stop before cutting yourself as the tomato separates. 
I can tell when the edge of the knife is starting to degrade because the gets harder to push through the tomato so I stop and strop and start again and the edge difference is obvious.


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## HRC_64 (Jun 24, 2018)

OK, I was picturing diced tomatoes done in hand and cringing...:lol2:


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## K813zra (Jun 24, 2018)

HRC_64 said:


> OK, I was picturing diced tomatoes done in hand and cringing...:lol2:



Like that fellow that dices the onion in hand on youtube? There was a link around here awhile back.


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## bahamaroot (Jun 24, 2018)

Depending on the size of the tomato I cut it into anywhere from four to eight pieces as I can them, turning the tomato in hand as I cut. I"m not dicing them into 1/2" pieces or anything crazy like that in hand. I don't always go completely through the tomato either but by the time they get through the canning process they have come completely apart.


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## HRC_64 (Jun 24, 2018)

K813zra said:


> Like that fellow that dices the onion in hand on youtube? There was a link around here awhile back.



[video=youtube;3wlgNYVRN7Q]https://www.youtube.com/watch?v=3wlgNYVRN7Q[/video]


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## K813zra (Jun 24, 2018)

HRC_64 said:


> [video=youtube;3wlgNYVRN7Q]https://www.youtube.com/watch?v=3wlgNYVRN7Q[/video]



Yeah, man. That is not for me!


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## domgro (Jun 28, 2018)

This is very interesting.

I have two questions:
1. Which (common) kitchen knives do have low edge angle?

2. If the edge angle is i.e. 30°, can I sharpen the edge angle to lets say 15-20° or isn't it possible?
sorry if this is a dumb question, I'm a noob when it comes to knife sharpening


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## Drosophil (Jun 28, 2018)

To answer both questions: you can put whatever angle you want, provided the steel can take it. Soft steels can't hold a thin edge for very long before rolling.


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## domgro (Jun 28, 2018)

ok, thank you


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## paulraphael (Jul 21, 2018)

This is convincing for test case of cutting soft, very abrasive material. The question I have, is to what degree this simulates cutting food on a normal cutting board. 

My impression is that my knives don't dull primarily from abrasion, but from edge failure of one kind or another. Maybe this reveals a problem with my knives or my sharpening technique. Has this organization done any systematic studies on the causes of dulling, which have led to this particular test?


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## Barmoley (Jul 21, 2018)

It seems to make sense that wear is not a primary dulling mechanism of kitchen knives and yet we see that in general more wear resistant steels hold their edges longer when cutting food. Given a good heat treat of each, even at similar hardness
blue super>blue 1>blue 2>white. 
The ones that hold the edge better have more carbides and are more wear resistant because of that, so wear must play a significant role in dulling when cutting food.

Larrin we need more tests......


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## Larrin (Jul 23, 2018)

More tests will come. Don't worry! I would imagine that even if the food doesn't wear the knife very much that the wooden cutting board might. Deformation and chipping of the edge while chopping/slicing against the board are also important mechanisms.


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## bahamaroot (Jul 24, 2018)

There is no arguing that deformation and chipping play a major role in edge life but I also believe acids can and do play a role too.
If acids can etch, patina and rust a steel how can it not affect edge life?


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## Nemo (Jul 24, 2018)

bahamaroot said:


> There is no arguing that deformation and chipping play a major role in edge life but I also believe acids can and do play a role too.
> If acids can etch, patina and rust a steel how can it not affect edge life?


I suspect that you are correct however the only way to know for sure is to do the experiments.


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## masibu (Jul 25, 2018)

Id like to see a test involving the use of microbevels of various grits/angles to compare to the dmt 600 without one. Lower grits perform better at low angles for increased aggression but for really high grits (depending on the knife) higher angles seem to be more stable without losing much cutting ability. 

For simplicity I would use the same 'knives' as used here throughout the experiment as pure carbon alloys don't require the same high angles as stainless. I don't have a scientific background to prove microbevels work I just know they do. It would be interesting to see if that translates on one of these tests and by how much the edge thickness changes.


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