Coarse vs fine grind and edge retention

[grepper]

Interesting study on how the fine and coarse grit finishes of an edge relates to edge retention.  I was surprised by the results.

I think it may be particularly applicable to general use and kitchen knifes where probably more slicing is done than straight push cutting.  When sharpening knives for someone else, it might be a good idea to ask exactly how the knife is going to be used.  Without that information, for a general use knife, maybe shoot for much less than 1000 grit.

I generally do kitchen knives to about 600 grit, but just for grins it might be interesting to half that and see how the longer term results pan out.

Interesting stuff:

http://www.cliffstamp.com/knives/articles/grits.html

http://www.cliffstamp.com/knives/forum/read.php?3,37143,37143#msg-37143

[Ken S]

Grepper,

This is fascinating. I think "the answer" will have many facets, not the least of which is the desired finish left on the material being cut. We must also consider the use. Do we favor an edge which will cut for a very long time with reasonable keenness or with high keenness for a shorter time?

We get into the turner's situation of comparing reshaping with resharpening. We get into the cabinetmaker's desire for highly polished edges, both bevel and back. We get into rough cuts versus finish cuts.

Jan's Viennese cabinetmaker whose shavings are no thicker than cigarette paper might settle for thicker, less elegant shavings for the initial leveling of a board and for interior surfaces. (He would probably settle for his apprentice's lower skill level for this labor intensive part of the work. )

Once again my time is cut short. I hope others will carry on this conversation and I will return later.

Good topic, Grepper.

Ken

[Jan]

Grepper, thanks for posting this link. It is quite extensive study! 
The results are interesting while unexpected. 

The major result that coarse grit can increase the edge retention on a slice was surprising for me. In the discussion the mystery was partially revealed: coarse grid edge behaves similarly as a serrated edge or a saw on the micron scale.

Perhaps the most important for the obtained results was the fact that the test medium was very soft. In the article recap we can read that in harder and stronger material higher grits perform better.

I think that our everyday vegetable cutting is done in much harder and stronger material then the tested medium. My recommendation would be to repeat the test with a medium of realistic parameters and also not with freehand sharpened blade. Freehand sharpening using coarse grits cannot provide consistent edge for subsequent testing.   

Jan

[grepper]

While hemp fibers are considerably tougher and therefore more stressful on a cutting edge than say broccoli, carrots or other general foodstuffs, I think the major consideration in relating these tests findings to sharpening for real-world applications such as kitchen knives is that this test is limited to non-impact slicing and push cutting.

Without personally derived empirical data, it makes sense that a "toothy" edge, due to the large percentage of the edge being comprised of laterally unsupported peaks in the uneven surface, is not as resistant to impacts as a smoother, more uniformly supported edge.

With kitchen knives for example, the edge is likely to suffer repeated impacts into hard surfaces such as a wood cutting board when chopping vegetables.  Assuming the inherent structural integrity of the steel peaks in a toothy edge is insufficient to withstand impacts with a wood surface without bending, it stands to reason that these peak areas of the edge would dull more quickly than a smoother, more fully supported edge.  This is a somewhat different scenario than a pure slicing environment with more even edge wear as described by the author of the test.

I can imagine what this edge would look like; a mountainous terrain with lots of little bent peaks with valleys between.  Depending on what is being cut, this might, possibly, be advantageous as the edge would become shaped like a mini chain saw blade, grabbing and sawing through surfaces like tomato skin more readily.  Or, maybe, just become dull more quickly. 

I really don't know exactly how to apply the test results to real-world sharpening, and I suppose it depends on exactly how the blade is going to be used, the bevel angle and the hardness of the steel.  The author was in some circumstances describing some pretty coarse ground edges.

Anyway, I thought it was worth punting out here as food for thought.

[Jan]

Grepper, it was definitely worth to draw our attention to this interesting article. I am glad to know about it. 

The article has a high level of professional ethics and does not withhold things that the author may not like. It's fair. 

Jan

[RichColvin]

Really interesting, & really surprising!!

[Ken S]

I have a problem with the coarse/fine test. I do not mean to criticize the author of the test; my own tests suffer from the same deficiency. To his credit, the author has used a variety of sharpening media, and his testing procedures seem well done and honest. Kudos for that. My problem is that only one knife appears to have been used in the testing.  I can't immediately recall the exact name of the knife used. As I remember it was a typical "garden variety" kitchen knife. That's a good general choice, however, it is a specific test. Would the results be the same with a variety of knives, including high end western and Japanese knives? (If so, why do we have so many alloys?)

I have done the same thing with my chisel tests. I have standardized on Irwin (formerly Marples before Irwin purchased the company and moved production from the UK to China) Blue Chip chisels. They are widely used, and, mostly, they are inexpensive. Mine cost just over $9 US each. My testing would be more complete if I included some Lie-Nielsen A2 chisels, Veritas PM-V11 and O1 chisels, some vintage Stanley 750 chisels and Japanese chisels. The tests would be better, but more expensive and time consuming.

Do my test results carry over from my eight dollar chisels to premium chisels? Does my specific case accurately reflect the general case? Does the coarse/fine specific, one knife case apply in the general case?

I applaud the coarse/fine tests as a good step in the right direction. They are well done indicators. However, like my own tests, there is more work to do. If only we had larger testing budgets and more time.........

Ken

[grepper]

I agree Ken.  That test is certainly limited in scope, and instantly begs more questions than it provides answers.  However, the next time I need to cut a bunch of ½" suspended hemp using a 2" draw with a 3Cr13 / 420 or other similarly soft steel blade, I will defiantly keep it in mind! 

It might also hold true when cutting other equally or less hard materials in a way that does not result in edge impact on a harder surface.  I suspect that blade impact on something like a cutting board might well change the result.

Ken puzzled, "Would the results be the same with a variety of knives, including high end western and Japanese knives?"

He, sort of, addressed that briefly; "More recently a Delica in ZDP-189 looked at the edge retention as a function of apex angle alone, holding the angles constant and the media cut was used 1/2 inch polypropleyne rope. It was found, as is shown in the image on the right, that while the very coarse CBN finish does have a lower initial sharpness, it has a significantly higher edge retention."

ZDP-189 and M66 steel is some of the hardest steel that I have seen in commercial kitchen knives with average HRC around 64-65 and can be as hard as HRC 67 or so.  Sort of the opposite end of the spectrum from 3Cr13 knives that if Googling around serves well is generally in the very low HRC 50's. 

That being said, I'm going to take Chris Stamp's word for it.  He is the author of the https://scienceofsharp.wordpress.com/ site.

Would there really be a noticeable, real-world difference in edge retention after a day of rope cutting between a more or less coarse ground edge?  I could be wrong, but I rather doubt it, and think the knife would need sharpening at the end of the day regardless.  Nonetheless, it's academically entertaining, fun to consider, and the principals behind it informative.

In the end, I think that steel hardness and bevel angle have far more influence on edge retention than does a more or less coarse bevel finish. 

Here is some very interesting real-world testing by Chris Stamp.  Sadly, not every knife shows the HRC, and you have to click through to the knife details to see if it is included.  Suffice it to say, that the best performing blade, Spiderco K08 is HRC 60-61 and the middle of pack Everyday Basics Santoku is HRC 50-55 depending which model and what steel was used.  I'd be willing to bet that regardless of a coarse or fine finish the Everyday Basics Santoku would be much duller at the end of the day than the Spiderco.

http://www.cliffstamp.com/knives/reviews/kitchen_edge_retention.html#1

More food for thought:

https://www.youtube.com/watch?v=60vOrJsGYu0

[Jan]

Thanks for a good food for thought, Grepper, appetited. 

Jan

[grepper]

Here is a site I really enjoyed.  Maybe you will too... 

It shows a comparison the edge retention, hardness and wear resistance of various steel compositions.  About 70% of the way down the page there are some nifty graphs that make comparison quick and easy.  Notice the high correlation between hardness, edge retention and wear resistance.  Note however, the hardest steel does not always offer the best edge retention or wear resistance, but always has high correlation.

CPM-S90V steel looks interesting.
https://www.heinnie.com/blog/complete-guide-knife-tool-steels/

I've read a bunch of reviews saying the super steel steels such as  zdp189/M66, S90V and their ilk actually are significantly better at holding an edge.  Tough to sharpen, but may well be worth it if edge retention is the goal. 

I'd really enjoy having a super steel knife to play with, but the cost vs is it worth it to me equation always keeps me from pulling the trigger.  A 6" M66/ZPD189 Twin Cermax knife for example costs like $250.00 and an 8" chef's can easily run $400 to a whole lot more.

All of my cutlery is your basic, run of the mill Calaphon, Wusthof, Victorinox, etc. and I hate them all.  I hate them all because they are all really sharp and currently there is nothing left in my house to sharpen. 

[Ken S]

Very good posts, Grepper. I am glad we have more knife saavy members than me on the forum. No false modesty; I'm an old chisel sharpener. I only got started with knives on the Tormek when I had a chance meeting with Steve Bottorff. I'm not one to pass up an opportunity to work with a master, and Steve has been a fine teacher and friend.

In fact, even the kenjig (knife setting tool) started as my method for setting chisel and plane bevels.

Edge retention seems like one of several factors to balance. If I should need major surgery, I hope the surgeon chooses the scalpel with the keenest initial edge (and that I am his first patient!) rather than being his sixth patient with a scalpel which retains most of its keenness for a long time. (I realize many surgery instruments are one use disposable items....sad waste of good steel, but more sanitary)

I find this kind of topic fascinating.

Ken

[WolfY]

Thanks for the links Grepper.
For knife sharpener, knowledge of steels and their characteristics is important.
I had the chance to sharpen a chef's knife with ZDP-189 steel. Big like Did it with the SB stone. The owner was afraid I would destroy it but asked me to give it a shot. Couldn't see happier person around for a while.

[Ken S]

Excellent post, WolfY.

Ken

[grepper]

Congrats Wolfy!  Sounds like you did a fine job and have a happy customer. 

If you don't mind, I'm curious; what make/model was the knife?  Did you find it difficult to sharpen?  Did the customer offer any opinion about using it?

It would be interesting to hear from anyone having long term experience actually using a ZDP-189 or other really hard steel knife.  Is the cost/edge retention ROI worth it?  Was it like dying and going to knife heaven?

Here is one dude's account I found of his experience with a S90V knife:

http://www.chefknivestogoforum.com/ultrafine-edge-retention-t7094-10.html

A video a little way down the page shows another guy cutting paper towel with a "used" S90V blade that has a very polished edge.  From personal experience, a polished edge easily cutting paper towel is generally pretty impressive.  Of course I don't know what paper towel he used, but some that I have is extremely resistant to being easily sliced through, especially with a non-toothy edge.

[grepper]

Video by Chris Stamp:
https://www.youtube.com/watch?annotation_id=annotation_489313&feature=iv&src_vid=mSt2mCWGFII&v=5At3NtNKHFA

I was going to start this by saying that I think everything I know is wrong.  But I think another poster puts it better saying, "Everytime I come to this forum the thought that I know something about sharpening my knife goes away."

Why I started this thread in the first place:

I was curious about what it the best overall grit finish for general purpose knives so that when I was lucky enough to sharpen for someone else I had a good standard to sharpen to for the best efficacy and edge retention.  Should I standardize on a coarser of finer finish?  Seems like a simple question, right?  To that end I was searching around and ran into the Chris Stamp stuff I linked to at the start of this thread.  I became curious because it ran contradictory to my understanding of edges, and considering the source I thought it worth noting

I've been at this for years, and have done a lot of research, but when I saw Mr. Stamp's data it was impossible to ignore.  I mean, I would far rather say oops I was mistaken and learn something new than to just stoically blunder forth in a stupefied, glassy eyed daze.

Since then, from a bunch of reading on the knife forums in posts from Chris Stamp, Jim Ankerson and others who are like..., very serious about edges, it seems the general consensus that a coarse ground edge greatly outperforms in both general usefulness and edge retention compared to a fine grind.  This is because of the way the "teeth" wear as the knife is used.  The one caveat is that the edge must actually be sharp.   For example, as far as I can tell, Jim Ankerson likes to stop at no more than 400 grit.

Now, generally, I take forum stuff pretty lightly, but these guys are, umm, how to put it...  Very serious about sharpening and edges and they perform a lot of tests.  We have all seen the work of Chris Stamp and the Science of Sharp site.  An example of Jim Ankerson's stuff:

http://www.bladeforums.com/forums/showthread.php/793481-Ranking-of-Steels-in-Categories-based-on-Edge-Retention-cutting-5-8-quot-rope

The discussion goes on and on and on and on about it in different knife forums.  Suffice it to say, there is a great deal of discussion.  Hours of mind numbing reading available.

Nonetheless, I'm starting to be convinced that some things I held as truths beg reconsideration.  How cool is that!  I think it's refreshing. 

Anyway, check it out.  Start researching Chris Stamp, Jim Ankerson, coarse, grit, edge retention, steel, knife... You know, all the terms and combinations thereof that you can think of to ferret out info in web land.  I'd be interested in what you all think.

http://www.byrd.cn/forumII/viewtopic.php?f=2&t=65731&sid=76375bc1c1ce1600a42a7e04079c3119&start=20#p979106