Knife feels duller with higher grits

Hi folks,
   A common issue some sharpeners have is that the knife seems to be not as sharp at 5,000 grit as it did at 1,000 grit.  The question is: Is the knife actually duller or does it just feel that way?


    It does happen and I am not absolutely sure why but I have some ideas and solutions if this is something you've experienced.  When I sharpen a knife, I always make sure that the knife is as sharp as I can possibly can on the first stone I use, all the stones of course but especially the coarse and medium grits, in other words, I don't rely on a finishing stone to get the knife sharp, it's already there by the time I get to that stage.

 

     I've had the opportunity to watch some people sharpen who have experienced this, i.e. knife is sharp until the individual moved up to 5k or 6k, it just seemed to get a little duller after that. In each and every case PRESSURE was the problem, too much of it. Once they backed off on the level of pressure things improved. I've been there and I've done the same thing.

     I'll go over the basics of what I think is proper pressure management, this is just the way that I sharpen, it works for me.

     Ive mentioned before that sharpening a knife is all about Burr Formation and Burr Removal and it starts of course with forming a burr. (After you've checked the knife anything that will hinder your sharpening, bent tip for example)

     The level of pressure that I begin sharpening with will be either heavy or moderate depending on the condition of the knife which will also determine what coarse stone I begin with, 120, 220, 320, 400, 500, 600 or 800 grit.  I need to use whatever pressure is necessary to form a burr. However, I always start with less pressure than I think I need, just to see how the burr forming process is coming along and in most cases it comes along just as I want it to.  LESS IS MORE - Remember that.

     Burr forming pressure only happens once on the one same knife. Once I have formed a burr consistent in size from heel to tip on both sides of the knife, everything I do next is about removing that burr, cleaning the edge. 

     Now that I have formed a burr using what I call P4 pressure I drop down significantly, a 50% drop in pressure as I don't want to form any more burrs and I have also moved to a medium grit stone at this stage, 1k or 1.5k (Shapton Pro 1.5k, I use it every day)

     Now comes the finishing stone and by this time I am using very light pressure and this may be the answer to the problem of the knife getting duller. If I used too much pressure at this stage, all that "cleaning" of the edge I just spent that last 10 minutes doing may be impacted if I use too much pressure and form a burr again. The burr may be extremely subtle, you may not be feel it and you certainly won't be expecting it. (Unless you are actually trying to form a burr which some people do, wrongly in my opinion but it's just my opinion).

     If your knife feels less sharp at 5k then it did at 1k go back to the 1k stone and use very light trailing strokes to remove any hint of a burr, to re-clean the edge and get it sharp again. NOW try the 5k stone, or whatever finishing stone you are using but really lighten up on the pressure. Use trailing strokes as if you are stropping on leather and see how it goes.

     The good news is that you can achieve startling edges with finishing stones, so the stones are not the problem, it's something else and in all likelihood it is a pressure problem.

5k, 6k, 8k, 9k and 10k
(I wonder why there are no 7k stones)

It takes time, patience and practice and more patience to nail down the pressure you use but again, LESS IS MORE, go easy, lighten up and concentrate on holding your angle, harder to do with added pressure. 

    Also remember that a good 1k edge can feel sharper as it has more teeth, more bite to it so if you think the knife is dull, test the edge, will it slice telephone book paper, arm hair?  (Ive done this myself,  it felt like the knife lost some of its edge but when I tested it on my arm it was very sharp)


Hope this helps
Peter

Edge Retention - Powerless

Hi folks,
     The topic of edge retention is one that has been swirling around on various knife sharpening forums for many many years, it is a topic that I don't will ever end because there are no finite solutions, no magic formula exists to increase the life of an edge. Please remember, these are my opinions only, I'm basing what I say on years of experience, a decade of trying to figure it all out and I have finally reached a place where I no longer lie awake at night thinking about it, believe me, I've done that.

   The reality is that as a knife sharpener, I have three duties that I should fulfil, tasks that will have my customers come to me for a sharpening service as few times as possible, to widen the gap between a full sharpening, to increase edge retention.  Now a knife owner has many more responsibilities than I do and there are also some things that we can't control. The steel the knife is made of, I can't change that and yet it is the key factor to consider, the quality, the hardness of the steel that the knife is made of greatly influences edge retention. (I will talk about my responsibilities later in this article)

   Here is the confusing parts, parts that I find confusing that is. We often hear the terms "polished edge" and "toothy edge" but what does this have to do with how long a knife stays sharp, I don't fully understand the science behind it but I will do my best to explain.

    On one hand, we have folks, smart people who are convinced that a toothy edge on a knife will last longer than a polished edge.  I don't know the answer but I don't think it has anything to do with the actual toothy edge (1,000 grit edge for example) as opposed to a 6,000 grit edge. Why would an edge that is not fully refined, a toothy edge, stay sharp longer and is it actually sharper or does it just "feel" sharper.?

This is not a toothy edge, it's just a picture of a knife I worked on. We can't see a toothy edge with our naked eye.

Some people say a toothy edge lasts longer, some don't agree and will polish the edge with no fear of it impacting edge retention, in fact they do it to enhance edge retention.

     Also,  are we talking about all knives or just the average, "soft" knives, knives with a hardness of 54-56, which encompasses a whole whack of knives. And hard knives, 60-67, especially all those dream knives that fall in the range of 63-64, what difference does it make if they have an 8,000 grit edge, which many do, they still have great edge retention.?

     Here are my thoughts on the matter, this is the way I solved the problem for myself. I have come to realize that a sharpener is almost powerless in his or her efforts to completely solve the edge retention issue, to make it go away because as I said there are only three things that I can do to promote good ER (Edge Retention) and yes I will mention them later on.

     I do not understand why a toothy edge retains its edge longer and I am not saying it does. What I do believe is that a soft knife, if over refined, in other words, if I sharpened it up to 6,000 grit for example can experience a poor ER. This is because the area behind the edge, the secondary bevel, the area that supports the primary edge is reduced in width over time, with repeated sharpening which in effect is weakening the primary edge.  There was a study by a group of engineers that determined this.

Here is the problem that I have with all of this:

    Let's say we had 20 identical knives and sharpened 10 of them to 5,000 grit and 10 to 1,000 grit. Then, we cut the identical food products, or something until the edge failed. We did this with both sets of knives and then, maybe, we could see results that would lead us to believe that the 1k edge did indeed last longer.

     This is all fine in a laboratory type of environment but once a knife leaves my hand, who knows how it will be treated. where it will be stored, how it will be washed and what type of cutting board will it be hitting on day to day basis. How will the knife be maintained, what type of Steel does the owner use, if any and is the owner have skill with a Steel or he is just slapping the knife against it and removing the established edge? (I remember bringing a freshly sharpened knife into a chef, it was extremely sharp and the first thing he did was use it open a heavy plastic wrapped cut of meat, that 30 seconds took the edge off.)

(Don't worry, I will provide what I think is the best edge in terms of sharpness and edge retention.)

  Now from a physics point of view, a polished edge will not only slice better but will have improved edge retention. According to the author Chad Ward in his awesome book An Edge in the Kitchen:
He writes about Force equalling pressure over area and an edge 1,000 of an inch thick and one pound of pressure concentrates 1,000 pounds of pressure per square inch at the edge. On the other hand, a toothy edge is like a fine row of needles with each point coming under pressure, so these individual points are on their own and wear down and roll over. You cannot argue the science here. I am just telling you what he wrote, I didn't write it but I have to agree with it.

We are talking about kitchen knives here cutting food, not an edge designed to cut rope and cardboard.


Here are the three things that I can do as a sharpener to help with edge retention.

Number 3:

Sharpen the knife at an angle that is appropriate for the given knife. I sharpen hard knives between 10 and 15 deg per side and I sharpen soft knives between 15-20 degrees.

Number 2: 

Finish the knife at the right grit, although the overall impact on edge retention is minimal in my opinion, when you consider the guy cutting a plastic bag open, whether I finished the knife at 1,000 or 2,000 grit is insignificant in terms of edge retention when you consider that the knife could be used on the wrong cutting board or chucked in a drawer. I finish soft knives anywhere from 1,000 to 3, 000 grit and hard knives can go up to 8,000.

NUMBER 1  
The most important thing that I can do is EDUCATE people, tell them what not to do with their knives and manage their expectations when it comes to how long the knife will stay sharp.


     In my opinion, the best way to keep a knife sharp is to ensure that it is thin behind the edge and the edge is clean when finished. This thinning reduces friction, a knife edge is under constant siege, it is subjected to a lot of pressure every day as it slices through a huge variety of products and then comes in contact with the cutting board.

 All that I can do is sharpen the knife to the absolute best of my ability keeping the rule number 2 and 3 in mind and then help folks understand that the edge is a microscopically thin strip of metal and it will fail eventually, so treat it with respect.


Peter

Controlling Space

Hi Folks,
     I know that my articles are not as frequent as they were but I am running out of things to talk about, I don't want to write something just for the sake of writing it. I want to wait until I find a subject that I think, and hope will be useful and interesting.

    To that end, this article is about finding a sharpening angle and learning to maintain that angle and once you can do that, everything gets easier, and sharper.

   Years ago I fretted about choosing the right angle to sharpen a knife at. I was afraid chefs would know that I sharpened their knife at a different angle than they were used to. That worrying was all for nothing, thousands of knives later and a decade passing by, not one chef has commented on angles, they never will.

    There is a simple method to find a good sharpening angle that you can use to start your sharpening journey, the PINKY ANGLE. (You can continue your sharpening journey with this angle as well)

(I saw this on a video by Shun, I didn't come up with it but I have used it to teach many novices)

    All you need to do is place the tip of your pinky between the spine and stone and you will create an angle of about 16 deg, it's approximate but it's good enough. Remember, it's not the actual angle, it's the ability to maintain that angle, whether it is 15 deg or 17. 5 deg, your goal is to be able to keep that angle stable, to control the space between the spine of the knife and the stone. You control that space and sharpness follows.

    Once your muscles have adapted to this angle, once muscle memory has been achieved,  than you can easily manipulate that space to arrive at and maintain different angles. I only use two angle so sharpen at, a Dream Knife angle of about 12 deg per side and an Average Knife Angle of about 19 deg but again, sharpening your knives, all of them at the pinky angle is fine, use to to build muscle memory.


   

    Learning to sharpen a knife by hand isn't difficult but it is not easy, if it was, everyone would do it.

The process itself is easy to learn. The hard part is actually committing yourself to practising, to creating muscle memory.  You need to learn to control that space, sharp knives are inevitable after that.

Manage your expectations though, we all learn at different rates. 

Always remember the four Pillars

Passion,

Practice,

Patience, and

Persistence.

Peter