Edge Retention/Rolling Test Stand

[grepper]

And, thank you Mr. Bud. They are beautiful roses! However, if you send me flowers again please choose a less dangerous variety! I clumsily grabbed one to partake in the delightful aroma and promptly stabbed my finger on a very sharp thorn. I felt extremely stupid for having done so. After all they were sent from an experienced and talented blade sharpening Exchange member!

[grepper]

There is another way to look at the oddly similar resistance to dulling comparing the RHC 55-57 blades to the RHC 60-61 blades.  One possibility of the similar performance is the thinness of the edges cannot be compensated for by using a harder steel, and that the forces applied to the edge during cutting operations simply negates the increase in hardness.

Another possibility is that the edges have been reduced in hardness by the sharpening process to the point where they are of similar hardness.  Softening of the edges could occur due to flash or background heating as steel is brutally torn from the edge by abrasives as Mr. Jan has suggested, or possibly metallurgical changes due to plastic deformation or both.  But I’m talking above my pay grade here, and simply passing along explanations offered by more knowledgeable sources.  I’m not so concerned about the “why” here, but rather simply offering edge softening as a possible explanation of why the two blades perform similarly.  

To me, the odd ductility of burr material is indicative that something has changed in the chemistry of the steel.  It has been postulated in this forum that this can be explained simply as a property of very thin metal.  Maybe.  I don’t know, as once again metallurgy expertise over my head.  But if indeed the properties of the metal have been rendered more ductile than can be explained away as simply thinness, then it seem reasonable to question how deeply into the edge does this ductility go.  

Assuming that the edge has indeed been rendered more ductile due to sharpening, I would assume that this increased ductility would gradually dissipate as distance from the edge increases towards the center of the blade.  Just a guess.

This is oddly contradicted by the apparent propensity of Shun blades to chip when only chopping vegetables, as though the edges of those blades are hard and brittle right to the edge.  But conversely, that is not what the SET (Structural Edge Test) data suggests.  Confused?  I am.

Maybe it’s a combination of force applied during cutting negates the difference in hardness of RHC 55-57 blades compared to RHC 60-61 blades, and that the edges have both been dehardened during sharpening.  To me it seems that the SET data leans toward the latter, and that both edges have been rendered to more or less equal hardness during sharpening.  

Fun stuff to ponder.

[Mark Reich]

Hm. Interesting things going on here, along with the appreciated comedy relief.  

The Jaques Pepin video is informative, but pretty silly. Mr. Pepin showed how one should operate a knife at the 2:45 mark, but it is obvious that he only uses  that motion as a demonstration. The only time he wasn't chopping, rocking or dragging sideways is when he showed the "correct" slicing motion. Otherwise he was constantly chopping, which was odd for a video of "proper technique" by a professional.

To be fair though, I think chopping is a necessity for efficiency, and if you chop lightly, straight up and down as Mr. Pepin does, I don't think it's unnecessarily hard on the edge, but a lot of people cut with a rocking motion. In other words, the front to middle of the blade stays in contact with the board while the blade is rotated. This is actually what is very hard on an edge. If you think about it, it torques the edge like crazy, resulting in rolled and/or chipped edges, depending on the steel.

Most people that actually bone meat (such as cutting up wild game) do it in a way that really magnifies this effect, unless they are cognizant of it.

There is a very good book, "An Edge in the Kitchen" by Chad Ward, which is probably the best selling kitchen knife book in history. I got it years ago when it was the #1 best seller. It will come up by the time you search "an edg". I haven't read it since I got it, but I'm going to try to find it to read again.

Oh yeah, if you read from the Shun site, chipping occurs from oxidation as much as anything, And they are speaking of stainless steel.

[EOU]

Just rusted a chip right through it.  Our money was on steel eating bacteria Mark.

[EOU]

Great food for thought Grepper and thank you very much for asking the questions. This thread seems to draw a large number of views but it seems that we are addressing a room full of crickets most of the time so your post is much appreciated. You hear plenty from us so perhaps someone else will join you in a conversation.

We're on a roll (pun intended) around here. Tell you the truth, this is very interesting stuff. Even more so once we saw the results of the test we're posting now. 

We're back to the far side of the world again and this was our next test subject:

                           

So $150.00 knives to $5.00 knives. We must have a dozen of these laying around here that we have used to conduct various tests but purchased two new ones today for the test. We used one and conducted two tests simultaneously on a single blade. This was accomplished by creating two different sharpness levels, immediately adjacent to each other, on the same edge. Out of the box the edge measured 286 and after deburring measured 168. We then separated the edge into two halves with tape over the edge.

                         

We then sanded the edge apex, out to the point, until we had a sharpness level reading of 291 then removed the tape. So now from the tip to the midpoint we have an edge that measures 291 and from the midpoint to the handle 168. The idea is to roll across the intersection of the two sharpness levels thereby testing the effects of rolling on sections of edge that have two different initial sharpness levels. The comparison was almost startling.

After one set we took our edge tester measurements and, of course, we have to take two measurements at two different locations on the blade. Sounds confusing so how about this; one measurement at each of two different locations.

1 set   (291 begin) now 380        (168 begin)  now 592     

168 to 592 after one set??? This was amazing! We had to take another reading at a slightly different edge location to confirm.

[EDIT 3/24 - Turned out the following day that there was a reason for this "amazing" number. Apparently the factory had left us with a very nice wire edge on their knife and this had a significant effect on the roll result. We sharpened the knife in-house and conducted the test again. The numbers from the section of the blade that we dulled and then conditioned are valid. The factory edge (168) numbers are not. The retest began at a sharpness of 164 and after 1 set finished at 435 which is much more in-line with other knife results. Big difference. Live and learn.]

 We got 602 on our second measurement so the huge roll on the sharpest side of the blade was for real. Back to the SET for two more sets of edge rolling.

3 sets (291) 473                        (168) 704

5 sets (291) 595                        (168) 805

So both sections of the blade just continue to roll at a fair clip and we just weren't that interested in hanging around to see where they would stop. In this test it is abundantly clear that the sharper portion of edge rolled at a much greater magnitude. It would also appear that we've reach a quality point nadir where steel, hardness factors etc. begin to really weigh in. No real idea on hardness but if it was over HRC 53 we'd be quite surprised. If it was 50 we wouldn't be surprised either.

[KnifeGrinders]

Even at this initial research stage the test results have proved the fundamental concept change that it is not the edge angle for the purpose, but the edge sharpness.
That's why felling axes are sharpened at 25 degrees included, the same as kitchen knives, just not the same sharp.

The test results prove with an exact science precision what had been advocated by Cliff Stamp over 10 years ago, and what Grepper meant saying
"Our esteemed Exchange member Thomas (Edgepal) has often stated something to the effect that no edge should be sharper than is needed for a particular task, and that the task at hand determines the blade used."

The conventional concept that 40 degrees included edge is for chopping, 30 degrees for cutting and 20 degrees for slicing has been made terminally outdated by the SET.

The other day we discussed the "edge angle for the task" with Youngbin (SHARPCO) who sharpens for living, and given the new SET data, I have updated my website changing our default edge angle we sharpen for customers at, from 30 degrees included to 20 degrees for quality knives and 24 degrees for mainstream, no matter chopping or slicing knife - edge sharpness will be fitting the function, not the angle.
When Grepper says "I think this offers a huge opportunity for both knife makers and sharpeners." - mate, this is already happening.

[grepper]

Mr. Mark,  just to throw Mr. EOU into a tizzy, I must say that was a most perspicacious observation you made about Mr. Pepin’s propensity for chopping.  Even though I don’t cook much more than fried eggs, I like to watch other people do it, and I’ve seen most all of Mr. Pepin’s cooking shows.  He constantly chops.  Chop, chop, chop, chop.  He’s very fast, accurate and looks at the camera while doing it.  He’s an accomplished super chopper!

He also has another interesting little habit in that before commencing chopping he likes to give the blade edge a single, fairly substantial whack against the cutting board.  He does it almost every time, and every time I cringe.  But considering how greatly his knife skills exceed my own, maybe I should stop cringing and think of it as a teachable moment (a phrase I hate).

“Oh yeah, if you read from the Shun site, chipping occurs from oxidation as much as anything, And they are speaking of stainless steel.”

Yeah, I saw that too.  While I inwardly chuckle and think maybe it’s just an excuse for not so durable steel, Mr. MaxTheKnife, who has sharpened more blades than I will in my lifetime, has stated in a post here that something like 98% of the Shun knives he sees are chipped.  If memory serves, he attributed some of the chipping to chemical corrosion from people putting the blades in the dishwasher.  I have no idea, just passing along the info.

That said, I do find it puzzling that Shun, makers of high end quality blades, declares in their main FAQ that in order to successfully make it through chopping the dinner’s broccoli without damaging the blade, one must proceed with care, and only employing proper slicing technique. Really?

My money’s on a Reich Precision blade, designed and proven to do real work.  

BTW, Mr. Mark, ever consider making kitchen cutlery?

[Bud]

What a load of #### that is. $150.00 bucks for a knife and it's a snowflake. Interesting test with the cheap knife. Goes to show that just not any knife will do the job. The cheap knife wasn't too much better than the cold rolled steel. At least the sharp side. I wonder if we're going to find out that the sharpest edge may not be the best edge for lots of things. 300 edges used to be my best effort. Now I don't think I know anymore how to sharpen an edge that dull. May have to get out the sandpaper like EOU did.

[grepper]

There is a lot to ponder in your latest $5.00 knife SET test Mr. EOU, more than I wish to in this post.  I would however like to comment on the results of the sharper 168 portion of the blade because that was sharpened most closely  to the other tests performed on  the unhardened and the HRC 55-57 and HRC 60-60 blades.

The latest $5.00 blade, RHC 50ish, performed better than the cold rolled blade, but not as well as the RHC 55-57 blades. This suggests that harder steel is producing a blade more resistant to dulling, but only to a point.  I say only to a point because the HRC 55-57 and HRC 60-61 blades performed similarly to each other.  

In other words, it looks like HRC 55-61 blades perform similarly, but anything less hard suffers noticeable performance degradation.  Almost like you have further defined the bottom fence.  Maybe we could suppose that RHC 55-61 is the “sweet spot” in producing blades that are not too hard to sharpen, are not overly expensive and have similar performance.  Maybe that is why all of the common blades we see lie within that hardness range.  Duh.

However, it makes me wonder if there may be a next level of increased performance in, say, hardness HRC 65-67.  A upper fence delineation.  But that is mostly out of curiosity and I really don’t care that much because from what I’ve seen the blade would be excessively expensive, probably very prone to chipping and way too difficult to sharpen.  

I do think it would be interesting to perform SET tests on the two blades HRC 55-57 and HRC 60-61 both sharpened to, say, an initial sharpness of 300.   I have a suspicion that harder HRC 60-61 steel may perform much better than even slightly softer steel such as HRC 55-75 when not over sharpened.  It could very well be that our proclivity to over sharpen edges chasing the dubious and less than useless “scary sharp” negates and obscures the real benefit of  fine hard steel.

Umm, congrats on sticking with your vision of the SET and bringing to fruition.  It seems to be producing data that is incredibly useful, and is answering very long standing questions that up to this point have only been uselessly blathered about ad-nauseam without resolution.  Methinks it is an amazingly admirable accomplishment.

[grepper]

Mr. KG, “Even at this initial research stage the test results have proved the fundamental concept change that it is not the edge angle for the purpose, but the edge sharpness.”

I don’t know if I completely agree with that.  Not saying that I disagree, I mean at this point I'm open to just about anything, but I would like to think that a less acute bevel is less prone to rolling than a more acute bevel.  

That said, I would be completely open to learning that initial sharpness has much more influence on resistance to dulling than bevel angle.  Every day here on the Exchange I seem to be presented by facts causing me to think that everything I “know” is wrong!  How cool is that!

I do agree that the SET data, at least so far, conclusively shows initial sharpness is critical in regards to resistance to rolling.   It makes sense, seems common sense that a less thin edge is more resistant to rolling, and is actually sort of a relief because of those reasons.

“When Grepper says "I think this offers a huge opportunity for both knife makers and sharpeners." - mate, this is already happening.”

Very cool mate!  Very cool.  Not only are you open to change, but quickly adapting new methods taking advantage of new data as it becomes available.  I truly believe it is a huge opportunity, but only for those who are listening and realize the ramifications.

I thought I had the perfect 150 edge.  Not too sharp, not too dull.  But really it dulls quickly.  Now, thanks to Mr. EOU’s SET, I think I understand why and how to fix it.  Oh well.