Edge Retention/Rolling Test Stand

[KnifeGrinders]

EOU, thank you for taking time to explain everything that clearly - uncertainties all gone.

[Bud]

Good laugh Mr. EOU but its too late. I already sent the flowers to Grepper. I am very much looking forward to Shun test results. I hope that you do not disappoint me.

[Bud]

Forgot to make a prediction. Henkel equaled 220 grams of roll on the BESS - Shun will be 175.

[Bubby]

You're way off Bud. I say 174.

[grepper]

The beautiful posies arrived today.  Thank you Mr. Bud!  My little shop has never been more cheery or smelled as sweetly!   Now I’m thinking about hanging some pictures on the wall.  

Well, golly gee shucks Mr. EOU.  I red that post again taday and I find it real hard to even say that first senence. Musta been some short term thing after watchun a Jeperdy show on the TeeVee set.  What ever it was it seems to have wared off.

You guys have no idea what you are talking about!  I’m placing my bet @ 174.5 .

[EOU]

We've completed the first step in our Shun tests so can now announce the winner of the "Shun Roll Contest". Bud guessed 175, Bubby 174, and the always diplomatic Grepper 174.5. Under the official rules of "The Price is Right" game show contest where one tries to be closest to the actual price without going over, the winner is...Bud. We'll finish our tests and post the details later today. Congratulations Bud!

[EOU]

And thank you Grepper for posting in English. You must have used your dictionary this time.

[EOU]

OK we've rolled the Shun and due to popular demand we're going to post the results here. To make a long story short our new VG10 Shun rolled 232 points after one set. If you don't remember what a "set" is or the details of the test procedure refer back to our previous post #88 in a response to KG on the previous page. 

So here is our new Shun knife. VG10 steel core and 60-61 HRC. Beautiful knife.

                                                                                       
       Nice Box                                                                       Nice Knife                                           Micro of steel laminations

So first we see how sharp it is right out of the box.                             And then after a little stropping
                                                                                             

Then take a picture of the edge.
              

As you can see we have a microbevel here. They say the primary bevel is 16°. Don't know about the micro but assume perhaps 20°. Few visible scratches in the primary but the micro looks a bit on the toothy side. Now it's time to get rolling.

                   

We performed one set initially and then measured. 

                   

That's 396. So we began at 164 and ended after one set at 396. 396 - 164 = 232. Now we want to see how far the edge will roll with our 150 gram load by performing additional sets. We've included the data from our Target puchased Henkel knife and B-50 cold rolled as well for comparison.

                                                   

At the top of the column in parenthesis are the initial beginning sharpness values of the edges. As you can see the Shun and Henkel rolled very much the same during the early stages but the Shun pulled up about a hundred points shy of the 
Henkel in total roll. 

A couple of micro pictures taken edge-on of the rolled section and an adjacent straight section.

                                                              

Taken within the test area section, here are near and far pictures of the Shun edge after testing was complete. Shun, in their instructions, seem very concerned with cutting activities that might chip their edge. As you can see, Structural Edge Tests didn't chip the edge.

                                                               

Here's the best photo we could come up with showing the reflected light off the rolled edge section. Once again, the roll is substantial enough to easily hook a fingernail on. 

                           

[Bud]

I won! I'm going to Disneyland. Never been so that is nice. I'm mad that I didn't stick to my guns. My first thought was that the Shun would come out just like the henkel. I guess I lost my nerve. This is so interesting Mr. eou. Thanks so much and hope that you and the other testers start to look at all the other things that effect the quality of an edge. 

Mr. Grepper, I sent roses. They must have shrunk.

[grepper]

Very simply put, the data presented above indicates that when stressed under only 150gf, with a starting sharpness of 150-170, a RHC 60-61 blade is no more resistant to rolling, (dulling), than a RHC 55-57 blade until the edge has rolled to a sharpness reading of 500+.  I think we would all agree that 500+ sharpness is a dull blade in need of maintenance.  

To put it another way, as far as resistance to initial dulling goes, a $45.00 Henckel performs as well as a $150.00 Shun until the blades have dulled to 500+ sharpness.

To put that in perspective, 150g is not much force.  I placed a small potato (maybe 2” diameter) on a scale and cut it with a ~200 sharpness blade.  The pressure needed to cut the potato was ~4.5lb (2,041g) or ~93% more pressure than the SET (Structural Edge Test) applies to the edge.  

But wait!  There’s more!  A harder steel blade may actually be a disadvantage, not only because it’s more difficult to sharpen, but also more prone to chipping.  From the Shun website FAQ: https://shun.kaiusaltd.com/faq

“WHY DID MY KNIFE CHIP WHEN I WAS JUST CHOPPING VEGETABLES?
Chips can happen due to improper cutting technique. Shun Cutlery is designed to be used in a smooth, slicing motion—and never in a forceful, up-and-down “chopping” manner.”

Um, hmm… Jump to 2:45 into this video and watch:
https://www.youtube.com/watch?v=nffGuGwCE3E

I realize this data runs contrary to established wisdom and even common sense.  After all, it only makes perfect sense that a harder blade would be more resistant to dulling, right?  Right!  Absolutely right.  But, one of the reasons why it is not relevant to knife edges is because our blade edges are so thin and the amount of force applied to edges during normal use far exceeds the differential hardness advantage between RHC 57 and RHC 61 steel.

In other words, one brand of wet toilet paper may support the weight of 1 quarter dollar coin, while another will support 5 quarters before the dreaded tear through occurs.  5X as much weight!  But neither can a support a 5lb bag of sugar.  If the goal is to support a 5lb bag of sugar, the difference in strength in this case is irrelevant.  

There very well may be an advantage to a harder steel edge sharpened to a toothy 300+ sharpness with a thick 20° bevel angle compared to a similar edge of softer steel.  But, the presented data clearly shows no advantage with a harder steel blade at 150 sharpness and an acute bevel angle compared to a similar blade of softer steel.

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.  Great wisdom there methinks.

For me, this is causing reconsideration of the 150 edge that I have always held so dear.  I’m starting to think that for a general purpose blade, a 300 toothy edge will be far more useable, durable and require less maintenance.  After all, what is the point of sharpening to 150 if after cutting a bag of carrots the blade dulls to 300?

I think this offers a huge opportunity for both knife makers and sharpeners.  The key will be in understanding what steel, bevel angel and edge finish produces edges that perform the best for the task the blade will be put to.