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Edge Retention/Rolling Test Stand
We're on it Bud. Matter of fact we'll be back on it tomorrow morning having just manufactured yet another set of, hopefully, improved designed parts for the test stand. We hope to get a new report up on the Exchange yet this weekend.
Here it is Bud. We had to come in this morning to finish this up because our Saturday didn't go exactly as planned. We think that we are about there with our test stand. We added a feature that allows us to move the impactor relative to the blade as opposed to vice versa. We think that we have to come up with a different name for the "impactor" because the term seems misleading. There is no "impact" in this test. We very gently and smoothly rolling the edge. The new set-up works superbly and our readings seem to reflect the improvement. We used the same old chef's knife we've been using but newly sharpened.  Grepper would be disappointed in us. We began in the 172 - 180 range this time. Another go with the Kally would have repaired that shortfall but we had other things in mind this time. Here's a picture of our test knife after the test. 


We're not going to bore you with before and after microscopic edge pictures this time because there is little discernible between the two in consideration of our new methods. Here is how we conducted the test this time and the procedure includes a new wrinkle this time. First, we established a total piston weight of 150 grams this time. Points "A" and "B" are redundant this time and serve only to verify results. In other words, we want A and B to yield similar results. A, B and C began life at similar sharpness levels. 180, 172, 172 respectively but we had something different in mind for C this time. We ground the apex of the edge down, at the C location, very slightly. Here's how we did it:


The abrasive piece is 5 micron S/C mylar backed polishing film. The sanding was conducted just as the picture indicates. Very slight pressure. When we were finished, C no longer measured 172 but then 239. We try to be very careful when performing this exercise. We sand, then we strop the edge, then we clean and measure edge sharpness. We then put the knife in the test stand and rolled the edge in precisely the same manner at all three locations. We roll about an inch long section of the edge and then measure around the middle of the roll. Here's how we measure these days; we measure once right on the mark and then a smidgeon left and a smideon right of the mark. We then average those three readings. The greatest differential within sets of three measurements was 11% and the smallest 0%. So, not bad at all. 

Here's how the tests came out:

A began at 180 and rolled to 300
B began at 172 and rolled to 295
C began at 239 and rolled to 301

Interesting isn't it? In this case, they all ended up at the same place regardless of initial sharpness level. Lots of different sharpness levels, sharpening variations and roll levels (piston weights) yet to be tested though. Now please keep this in mind when we talk about measuring the roll. We're not measuring (as in inches or mm) edge deflection. What we are measuring is how the roll affects the cutting ability (level of force) of the edge. That's what we're all interested in though, how rolling affects edge performance. If edges could roll 90 degrees and not affect edge performance we wouldn't care if edges rolled or not. 

We think test stand refinement is pretty much done. We need to test some other edge variables just to get a warm and fuzzy feeling about our new device and then we think we'll be ready for some crowd (BESSEX member) testing.
Thank you EOU for the work you have put in on this. This is very interesting indeed. I think that this is going to answer a lot of questions about many things. First edge testers, then Rockwell and now this. What's going to be left to argue about?
Got to tell you, this is starting to be fun. We went to lunch and were talking about the new test stand and where we should go next. We've already decided that we're going to let our member testers figure out how higher HRC edges fare but we decided that shouldn't keep us from testing lower HRC knives. We just happened to have a perfect knife for the purpose. It's a knife cut out of a sheet of .030" spring steel. 


Mcmaster Carr says that it is HRC 50. We sharpened the edge at 19 degrees (our test standard) and 140 sharpness. Then we rolled it exactly like the previous chef's knife test. After rolling, the edge tested 440, 458, 449 or an average of 449. That compared to the average 300 of the Henkel chef's knife which we assume is somewhere around HRC 55-57. There are a few differences here that may not make it quite a apples for apples test (specifically the behind the edge thickness is quite thin here) but the difference in roll is quite notable. 

A 300 point roll is sizable and we cold easily hook our fingernail on this one. Using a Sharp Pad we were only able to straighten it back to 228. We used me2's trick then using the spine of the Henkel knife and got it down to 198 but that was the end of the road.
(02-18-2018, 01:19 PM)EOU Wrote: Here's how the tests came out:

A began at 180 and rolled to 300
B began at 172 and rolled to 295
C began at 239 and rolled to 301

(02-19-2018, 04:57 PM)EOU Wrote: After rolling, the edge tested 440, 458, 449 or an average of 449. That compared to the average 300 of the Henkel chef's knife which we assume is somewhere around HRC 55-57.

Just to play devil's advocate, is it possible from these test results we are effectively seeing another type of hardness testing, but instead of being an indent in the side of the blade, it is the actual edge hardness we are seeing?

My concern there would be that rather than actually see a different between steels, we will only see the actual edge hardness.

With the first test ending up at the same BESS score regardless of the starting condition, and the lower hardness steel ending up at a higher BESS for the same test conditions, it feels as if what is happening is that the steel is becoming deformed until the pressure applied can be supported by that deformed, widened pad of steel.

I'm very interested in this test, but this is what stands out to me from those results.
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Excellent thoughts subwoofer. You're not alone in your advocacy. We're all entering an area where no man has set foot before. We're all devil's advocates at this point. I can assure you, we have no agenda here and few theories. At this point, the only thing that we can tell you for certain is that we simply don't know. We hope that your speculation is correct, that we are testing edge hardness and/or durability because that is where the rubber meets the road in most applications. In fact, if your speculation is not correct then we are likely wasting our time here. 

We hope that there is a general correlation between hardness and edge durability (as this early test seems to indicate) because that doesn't rock the boat of conventional wisdom. We've rocked the boat before and it's no fun.  Assuming higher hardness steels roll less than softer steels then we get to explore all the other contributing factors like all the edge geometry issues, sharpening technique/methods etc.  Just quantifying the edge rolling characteristics of HRC 60 vs. HRC 62 is going to be interesting though. Then there are various steels that might both have identical hardness characteristics but do they resist rolling to different degrees? More combinations and permutations here than you can shake a stick at.

Our general goals with this device are simply this; to help separate reality from myth and to elevate speculation to a set of evidence based findings. That's the bottom line and thank you very much for your comments and participation here.

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