The 1,000 grit edge - Improved Edge Retention puzzle - Solved.

Hi folks,

      I should state right up front that with reference to the title of this post, it was a puzzle for me, I am not  suggesting that everyone out there was confused by the repeated statements that led me and others to believe that a knife finished at 1,000 grit will stay sharp longer than the same knife sharpened at 8,000 grit.

     It's not that easy, to be clear, this statement which I now believe to be accurate (with caveats) implies the sharpening of knives such as your basic and very common Henckels, Wusthof, Grohmann, Global and not the dream hand made Japanese knives.  It is the steel itself, the hardness of the steel that is important to get a grip on for this statement to make sense.  We know that the hardness of steel used to make knives can be measured and measured very accurately. Sharpeners and  folks who are knowledgeable understand this scale and what the numbers mean. It is the Rockwell Hardness Scale or HRC more accurately and I believe that stands for Hardness Rockwell Conversion.
Rockwell Hardness

Funny enough though, the majority of people who purchase knives are not too concerned about the hardness of the knife that they are purchasing. They are concerned about the cost of the knife, the way it feels, the way it looks but in my experience, (people bring me knives to sharpen daily), the hardness of the steel is not an issue.  It should be.

 
     The majority of knives I sharpen and the ones that are in millions of homes range in hardness from 54-58 and that is common, the higher the number of course,  the harder the steel.   Now it is good to know that the makers of knives don't simply turn up the Hardness Dial to make the knives harder. There is a very significant difference in a knife that has a hardness of 58 and one with a hardness of 60.  In most cases this also represents a substantial difference in price, the harder the steel,  the better the steel so the more expensive the knife.

    Why is harder steel better? 

     This is where the edge retention factor comes into play, a softer steel such as my Henckels will succumb to the pressures of everyday food preparation faster than my Fujiwara pictured above (on left) which has a hardness of 63.  I know that this is obvious but it is important that I lay the groundwork in order for this article to make sense.


    Before I continue I mentioned caveats and there are some that make definite statements questionable. For example, we should not read " A European knife sharpened at 1,000 grit will always stay sharper longer than one sharpened at 5,000 grit". This is not to say that the author of such a statement is trying to fool us because it is likely true without some obvious caveats.

    "Under most circumstances" is applicable to the statement because people treat their knives differently, they cut different things and the edges impact different cutting boards with different amounts of force. Those same European knives for example, one finished at 1,000 grit and one finished at 8,000 grit live different lives so this means the ability of those equal knives to hold their edges and equal amount of time is questionable.  However........this is all common sense, the important thing is that this is important to me, a sharpener, i.e. how to sharpen a particular knife. I can't control the knife after it leaves my hands so I cannot tell an owner how long that knife will stay sharp. I can tell him however that I sharpened his Wusthof at 1,000 or 1, 500 or even 2,000 grit to enhance it's edge retention.

    People will buy a knife without regard to these things, that doesn't let me off the hook, as a knife sharpener it is my duty to apply the appropriate edge to any given knife. Making a knife sharp is easy, making it SMART SHARP is something one needs to learn. I can easily sharpen a knife at a very acute angle and dazzle someone with the edge. That edge may fail on day one so I need to not only make it sharp of course but to try my best to keep it sharp and with this goes a little education to the owner.   I have always said that edge retention is a team effort, if the owner is going to throw that knife into a sink with 8 other knives, all my work will be for nothing.


     NOW with the help of some reading and a fantastic explanation from my friend and mentor Tom Blodgett of Jende Industries, I can explain why I did that. Before today, I lacked the scientific background and therefore the best answer to the question.  Tom's knowledge in these matters dwarfs my own, he knew the answer t to my puzzle before I knew that is was a puzzle :)

Why is a 1,000 - 2,000 grit edge better for certain knives?

     Again, the answer to this question has come to me recently and it follows a lot of digging, I mean a lot of it and also the fact that I have absolutely no problem asking questions and sooner or later and answer will come.


     This is my explanation, others that are more knowledgeable about this topic could word it better, folks like Tom and Cliff Stamp who I have never met but have a lot of respect for.  I can make your knives exceptionally sharp folks but there is more to sharpening than that, it involves a deep understanding, if you want it to involve that of course. I find the topic fascinating so it only makes sense to turn over every stone I can find.

     (First of all, we start with knives in the "softer steel range" this is not imply that they are inferior knives, these are common knives that fall into the budgets of many people. It took me thirty years to have a knife that is "hard".  Remember that hard knives, I mean really hard knives have issues to, yes they are absolutely incredible to cut with but they can be brittle and that astonishing edge can chip if you are not careful.)

Typical knives and a 1,000 grit Naniwa Chosera.

     As you know, the sharpening process involves grinding the two sides of the knife until they meet at the Apex and form the Primary Edge, we make that cutting edge as microscopically thin as possible and we make it as uniform as humanly possible. If I sharpen a Global knife at 15 degrees on one side, I sharpen it at 15 degrees on the other side, the closer I can get to 15 deg on each side the sharper that knife will be, since I do that by hand, it is obviously possible that I will be off a tiny bit, sometimes I will nail it, sometimes perhaps not. This is human sharpening not precision sharpening but I can tell you this, I will take the "human edge" any day of the week. :)

   Knowing that the average Global knife, a very popular knife falls into the 56-68 hardness category, I will sharpen it up to 1,000 or 1,500 grit. (Now don't think that because it isn't sharpened up to 8,000 grit it won't be that sharp, believe me, the knife will be sharp at 400 grit.)


   I have seen pictures of edges of knives taken with special instruments. (SEM, Scanning Electron Microscope) that provide incredible images of edges magnified 5,000 times. Now the edge of knife shot at that level doesn't look like the edge of knife but it does reveal important things, very important and it is these images and the explanation from that gifted one,  Tom Blodgett that enlightened me.

   The primary edge is thin, a somewhat fragile strip of metal and by thin I mean at the microscopic level.
The area directly behind that edge supports the edge, it helps hold it in place so to speak. Think of it as the Edges Armour.  Now the picture revealed that the same knife sharpened at 1,000 grit has a very slightly thicker Apex than the one sharpened at 4,000 grit. Now we are taking decimal three or decimal 4 microns (.3, .4) but this is enough to have an impact on the edge. The life of the edge is found in this molecular space and even a very tiny micro level of difference is a difference.

    It has an impact on this particular steel so if I sharpened that same knife up to 5, 000 grit, the area directly behind the cutting edge is a little thinner, I have created a weakness in the armour, and while this is a micro level difference, when you consider the life of the edge of a knife, that little difference is enough to make that particular knife's edge fail a little faster. So the 1,000 grit finish with it's minimal collateral impact to the secondary bevel is better for this particular hardness of a knife.

   So what if you want to sharpen it to 5,000 or 8,000 grit because you love the way it looks and cuts?
No big deal, remember all the caveats that influence the life of the edge of knife. It may or may not make a difference.  This article is simply an attempt to add some weight to the statement that a 1,000 grit edge is going to last longer on certain knives than a more refined edge. Now I know why and I hope I have conveyed that to you.


  Now, with a harder knife, 60 and up to 64 for example, that steel behind the edge of the edge, that armour is much much harder so I can refine it up to 8,000 grit, it will still support the Primary Edge.

Cool eh..

    Buy a knife you can afford and you can ask how hard the steel is and you could be surprised if you got an answer. Don't worry too much about that, there is a significant difference in price and in the forging process as well. Not everyone has the skill to make a knife with an edge hardness of 64, in fact the number of people who CAN do this is quite small in the big scheme of things.

   60 is a good number to shoot for but just get a knife that you can afford and find a good sharpener and let him worry about these things.  ( I mean a good sharpener by the way and that could be the challenge) At least you now now....hopefully....why certain edges perform better than others.

I received this comment from a fellow sharpener that I have much respect for, it is important to share here as it is pertinent to what I was trying to say, some excellent points.

Well written Peter. 
A few more points to consider... 
Hardness is not a sole determinant of wear resistance. It is also the constituent elements added to steel like chromium, vanadium, tungsten and etc. that contribute as well. 
In addition it is not just the grit at which one finishes but how well the burr is removed at every step aiding in the strength of the edge and behind it: yet another "weakness in the armor". That is why jointing the edge works in keeping an edge long lasting.

Again......this is not information I was born with, I gained this information from people smarter than I am, I like sharing it that's all.


Thank you very much for reading this.

Peter Nowlan