Edge Retention/Rolling Test Stand

[grepper]

Have you noticed how Mr. EOU always speaks as "we" instead of "I"?

[EOU]

Okay. We're going to drive a stake in it. Just ordered the hardened rod and as soon as we get the rod in we're going to make the new steel platens. Let us see how/if it works and then we'll go from there. We need to produce a nice, broad range of effect i.e. really good edge = 50 and really bad edge = 300 so that differences are easily discernible. If it actually turns out to be 20 and 400 then fine but we don't want a range of 20 and 45 although 20-45 might be actually telling the complete story already. If you recall, people used to get thrown in jail for suggesting that the earth wasn't the center of the universe so if it turns out that indications are that there isn't much of a measurable difference, no matter the sharpening technique/steel/sharpness level, please provide references for a good bail bondsman. 

The relationship between edge impingement area and force is just going to have to be trial and error. We're going to begin with .3125 (pin diameter) and 5 Lbs. (added weight) and see what we get. We like 5 LBs or there about because that's about the force required for a sharp knife to cut a potato in two and it's a very manageable amount of weight to be working with. We don't want to be placing 50 LBs. on the piston platen so if adjustment is made it will likely be made by adjusting to a smaller impingement area.

Our experience tells us that test apparatus like this, right off the bat, give strong indication that there are significant differences to be discovered and in a reproducible fashion or they don't on one count or the other. This little gizmo has some hoops to jump through and some simple tests to pass before it sees the light of day. We should have something to report, thumbs up or thumbs down, end of next week.

[EOU]

You snuck that post in Grepper while "we" were composing "our" own. "I" don't always author the EOU posts but more often than not I do so Mr. EOU is just fine. As Ken might suggest, just think of "us" as the Borg.

[grepper]

"We are Borg."

https://www.youtube.com/watch?v=cvwFcbAmYQg

"We are Hugh."
https://www.youtube.com/watch?v=sRc8EyPoxOU

[EOU]

So, we had our new parts and about thirty minutes so decided to have a quick look-see at how things are going to work. Please don't accept these results as gospel just yet because we have neither repeated the test nor examined the process for errors. We did think that you might be interested in how we go about things of this nature though.

We began with a mid-range Henkel chef's knife. The knife had been sharpened at about 22 degrees and we wanted to make certain that it was subjected to some fairly extensive grinding so decided to change the grind angle to 19 degrees. We put a 80 grit ceramic belt on our Kally with custom guided knife rest and raised a burr. We then switched to 180 grit ceramic belt and raised another burr. We then removed the burr with a Sharp Pad, placed a marker near the edge, and then took a picture of the edge. 

   

Don't know where the black marks emanate from but there they are. We then measured the edge with a PT50A using standard test media fixture and got 166 and 171. Then we put the knife in a vise and set it in our new test fixture. We lowered the 5/16" diameter hardened rod down on the edge at the marker.


   

We added a 2000 gram weight to the platen. The piston weighs 140 grams so 2140 grams = about 4.7 lbs

   

Then we removed the piston and the knife from the vise and shot a couple more pictures. The first of the marker in proximity to the edge.

   

Then the edge itself.

   

Then we measured twice again. 166 and 166. That surprised us. We know that edges roll. While we need to repeat the experiment it may very well be that edges need more encouragement to roll than we gave this one. In any event, and assuming that this test holds up, sharpened edges seem more durable than we first gave credit for.

[KnifeGrinders]

We should read this result as an evidence of an edge that has been completely deburred.

Mike, would you be able to produce a feather/wire burr, and repeat the same test?
E.g. this type of micro-burr inevitably forms when after #1000 you strop an edge edge-trailing on a leather with 0.5 micron diamond paste.

[EOU]

We will give it a try KG but we all can predict the result of that test. We do happen to possess the best wire edge producer known to mankind. It's one of those ceramic wheel pull through sharpeners sold by a major knife producer. If you catch it just right (enough pull thrus but not too many) it will produce a wire edge that measures 110-120 and then 700 after you make one cut through a carrot.

[grepper]

I did some pressure tests once with a potato.  If memory serves correctly, slicing through the potato required 3-4 pounds pressure.  I didn’t do sharpness readings, but I would surely think that slicing a bunch of potatoes would show at least some dulling of a blade.  However, potato cutting involves impact with the cutting board.

So, what’s next?  Try more weight?  At some amount of weight crushing/rolling of the edge will occur.  For example, it would be very easy to seriously change the edge with a vice.  Maybe it’s just a matter of increasing the weight until enough edge deformation occurs to provide a useable range of sharpness readings.

[EOU]

Your post timing is excellent Grepper and made even better by the fact that we couldn't get this post up yesterday due to our host's server issues.
 
But now we're getting someplace. We decided that rather than take the time to repeat our first test that we'd just jump the weight up and see if we were on the right track at all. 4.7 lbs didn't seem to have much effect but 9.7 lbs. did. Same knife and edge location as the first test but we began this time with a little lower initial sharpness number after additional leather only honing on the edge. The edge, this time, measured 159 to begin. 
 
We put the knife in the test fixture and applied the 9.7 lbs at the platen and then removed the knife. Measured 429 and 445 at two different points. That's a lot of roll! But was it roll or crush? If the edge is crushed it won't come back with leather honing. We straightened the edge on a Sharp Pad and then took a lot of measurements and additional honing. The story didn't change with the additional honing/measurement efforts. At the estimated epicenter of the 5/16" diameter test point we got 229. Not bad but not perfect either. 1/16th inch to the side of that point we got 160 and we got 160 again when we moved the measurement point a 1/16th of an inch to the other side of the 229. These numbers were very reproducible. So, in a nutshell, the 229 was in the middle and flanked equidistant on both sides by 160's. Everywhere else inside the test area measured very close to 160. The reason/cause for 229 versus 160 was not visually discernible using an optical microscope.
 
So it was almost a perfect test sans our one 229. We got the kind of edge movement we were looking for, approximately 280 points, and fell just short of restoring the edge to its original sharpness level. A few adjustments and we might just get there. Past experience tells us that 300 points of roll on stainless steel knives is just about the limit. Beyond that, edges usually cannot be fully restored. A well designed edge test system might more accurately define this limit though.
 
This second set of measurements is very encouraging. Please keep in mind with these reports that, at this juncture, we're only testing the tester and the edge information presented is secondary to that purpose. Once we get our test fixture and procedure tuned in that's going to change. Then we might not have to speculate about many of the factors we think might be germane to producing long lasting and serviceable edges, we'll just know.

[Mark Reich]

IMHO, you may be able to test edge folding from normal things, like cutting board material.

This would take a lot more weight, against a softer surface than hardened steel, because the momentum of hitting a cutting board after a potato separates would be significant.

I'm not sure if that would be germane, or practical to estimate, but I certainly see the relevance of this new testing device!

Pretty exciting, and I'm very proud of the EOU crew!