EDGE RETENTION/ROLLING PART II

[EOU]

Forgot to respond to Bud's observation. Same thing as we've seen with many used industrial skives Bud. The corners seem to fold back first and in some cases really radically. Must be true, at least in some cases, in the woodworking biz as well.

[grepper]

...
The current design seems to produce "real use" kinds of roll characteristics. If the current design accomplishes this then we ask "why be more gentle with our test edges than real use itself is?" Here's the second reason; it requires multiple passes over the same point with the current SET force used (150 grams) to produce significant rolls. In fact it may take a total of some 50 -70 passes over the same point until maximum roll has been achieved. This indicates to us that we are probably not setting thumb tacks with a sledge hammer at 150 grams of force. 

What is important for me when considering the data produced by the SET tests is how it relates to real-world use of knives.  Considering that general kitchen use of knives exerts orders of magnitude more force on edges than the 150g SET tests, other than being intellectually tempting to ascertain how little force is necessary to differentiate HRC 54 and HRC 62 steel resistance to rolling is, it seems of little real-world consequence. 
 
I have to admit that I had always assumed that harder steel would have better edge retention, but did so only on intuition.  It makes perfect sense that it should. However, SET results indicate otherwise, and interestingly I don’t find that counterintuitive considering how thin sharp edges are.
 
Even lacking any supporting data, I still would assume that if the force applied to the edge was nominal enough that harder steel would indeed be more roll resistant, and I would even guess that hardness/force roll resistance could be proportional.  It’s just sharp edges are so thin that for knife use the hardness differential is irrelevant and inconsequential in real-world knife use.  

Mr. Jan has postulated that it may be explained with the “foil” effect.  I have yet to be able to understand that, so I’m guessing that it’s the sledge hammer vs egg effect.  Two eggs placed on an anvil may indeed offer twice the resistance to smashing as one egg, but when the sledge hammer slams down for all intents and purposes the difference in negligible.

[KnifeGrinders]

We’ve seen both in our BESS-SET tests and CATRA tests done by Larrin Thomas that mainstream and super-steels sharpness shifts from the shaving sharp to work sharp at near the same rate, but super-steels stay work sharp significantly longer.
The same with hardness - though the initial rolling/blunting rate is rapid regardless of the steel hardness, the higher is HRC, the longer the blade stays work sharp.

[Jan]

Thank you very much EOU and Mr. Grepper for sharing your views on this conplex topic.

For the time beeing I am not deepening the idea of the "foil effect", but rather considering how universally valid the obtained results are, and to what extend they may reflect some specific properties of the A2 steel. This includes grain size, carbide size, carbide hardness vs abrasive grain hardness etc.
Also the question came to my mind if sharpenning/honing could torn out some hard carbides from the matrix and leave a deffect in the edge.
 
Jan

[Mike Brubacher]

Good points all Grepper, Jan and KG. The work that has been presented in this thread and it's predecessor thread is far from all encompassing. If anything, we had questions before the study was undertaken and now we have more questions. There does seem to be a significant difference in edge rolling between steel that was not hardened and steel that was hardened but we could not find a very significant difference between steels that had been hardened to common knife ranges. Interestingly, our informal work with bevel angles and micro-bevels etc. did not indicate significant effect either until we tested our chisel grind edges and witnessed a very significant difference. It seems that if we look at the extremes i.e. bevel vs. no-bevel and hardened vs. non-hardened that we see clear and significant differences but if we look at the minutiae and stepped variations, any advantage of one over another is very difficult to discern with regard to edge rolling. 

It would seem to us that the term "significant" may be key here. 15%, even 25 or 30%, one way or the other may not have much meaning for the home chef but in one of KG's customers meat processing plants it might have profound effect. Perhaps this will be the take-away from the work that has been done to date. Each user has to decide what, for him or her, is significant and what is insignificant.

[grepper]

"...but rather considering how universally valid the obtained results are, and to what extend they may reflect some specific properties of the A2 steel."

Mr. Jan, I would be interested in your views on the above. 

Mr. KG noted, "The same with hardness - though the initial rolling/blunting rate is rapid regardless of the steel hardness, the higher is HRC, the longer the blade stays work sharp."  

There has been so much data posted here in different posts, I don't remember seeing that data.  Mr. KG, if you have the supporting data handy could you please repost it?

All this data is now sprinkled throughout various threads and posts.  I sure would be handy if all the various data was at least in one place!

[Jan]

Mike, you are master of concise summary, I like your recollections because it saves time and prevents misunderstanding.

 
Jan

[Mike Brubacher]

Deserved or not Jan, that is high praise indeed so I will simply accept the compliment and say "Thank You" for expressing it here.

[subwoofer]

I've been meaning to get these results pasted for a little while now. My first batch of SET results with a range of different knives.

I decided to focus on a couple of main ideas, degradation after series one and two, and degradation after a recovery strop. Of course these are closely related to the starting sharpness and edge angle.

The reason the Series 1 column says cycle 5 series 1 is that I was recording the BESS score after each cycle. This proved not to be useful, so I gave up.

You will see that in most cases the degradation after the recovery strop is negative meaning it got sharper. Clearly my edge preparation is not perfect, and my strop is quite effective.

Anyway, these results are what they are, so may be interpreted as you see fit. I will be continuing and working with more steels.

[grepper]

Sorry for being so thick-headed, but does series 1 mean you did one cycle (forward/back again) 5 times?