Wednesday, 17 August 2016

Pressure - clarified and since Updated

Under Pressure Video

Hi there,

     I received quite a few emails and comments about the subject of pressure while sharpening as it applies to the video I did which is linked just above. I long ago adopted a four tier pressure technique that I spoke about in the video. I intend to do another video with the hopes of improving the original. I think that there is always room for improvement and since I got some questions on it, I figured I would give it another shot, so that will be up on the Blog soon.

     The purpose of this article is just to state, clarify the technique that I use and I have no doubt that others use it, used it before I did likely. I am not trying to say that I invented something revolutionary,  it is more like I discovered something that was probably being used a long time ago by folks.

    Okay, as you know I used four levels of pressure on the first burr raising stone (only this stone) and then I reduce pressure on the subsequent stone(s). So on the first stone I use 4 levels of pressure and then I use 3 levels of pressure on every stone after that.

    This is the way I sharpen and I have done thousands of knives this way which may be your way too of course, as I said, I take no claim to this, I'm simply sharing information.


    I thought of different ways to demonstrate the amount of pressure that I use and recently used a kitchen scale in attempt to display the pressure. I have decided not to do that but to explain it.  Nobody is going to get a scale to measure the pressure anyway, it is very simple to gauge the amount of pressure to use and it may be slightly different with every single knife anyway. For example, when I did use the scale it measure between five and six pounds of pressure when I was using P4 pressure. However, that is for a very very dull knife, if the knife is not too bad, still dull but not so bad that it looks like a 30 year old edge that has never been sharpened, I would reduce the initial burr forming pressure. So common sense is going to come into play. Suffice it to say that when I want to raise a burr I use heavy pressure, I do not press down as hard as I can of course, I just press down hard enough to get the job done. 

    If the knife you are working on is not actually dull, it just needs a tune up you may not require this amount of pressure. This pressure is only used once during the entire process and that is to form the burr. Basically, it is the amount of pressure that all sharpeners use to initiate the sharpening process. This is nothing new, just press down hard enough to ensure the stone is doing what it is meant to do. You know of course that if you don't press down hard enough, nothing is going to happen so apply the appropriate burr forming pressure and keep applying it until you have successfully raised the burr on both sides, from heel to tip

    If you are just learning and not sure how much pressure you need, start with very little pressure and gradually increase pressure until  you can see, feel and hear the abrasive properties of the stone acting on the edge of the knife. 

   I use this pressure with my coarse stone, if you only have one stone, a 1,000 grit stone for example you can still do the same thing with a dull knife, if your goal is to raise a burr, use whatever pressure is required to do that. However, do not press down to hard, don't use so much pressure that your work is uncomfortable. 

    Strive for consistency, holding your angle, the amount of pressure you use must no interfere with your ability to hold your angle, so less may be more, modulate it as required and you will get the hang of it. 

     Now that you have a burr, the hard work is done and your knife will become sharp. The length of time required using heavy pressure (P4) will vary, depends on your knife, your stone and you. This is the most patience demanding period of knife sharpening. There are often times that I can get a burr raised very quickly on one side of the knife and it seems to take an eternity to get it done on the other side. So patience here, do not move on to another stone or reduce pressure until the burr is formed. Also, you may find that the burr forms on certain areas of knife before, the belly of the blade for example before the tip. So when you get to those areas where the bur IS formed, you should reduce the pressure and then increase once you move past it.


     I reduce my pressure when I have raised the burrs on the knife, (one per side). There is no requirement to raise the burr again on the same knife,  so the reduction in pressure will help here. Your goal now is coarse stone refinement, you now need to remove the burr completely. I reduce my pressure by half at this stage or very close to it. I sharpen at this reduced pressure moving from tip to heel and then back from heel to tip on one side and then repeat for the other side.  I am concentrating on holding my angle and visualising what I am doing. I am using the abrasive properties of the stone to remove the burr that I created, I'm shaving it off and this reduction in pressure will do it. Don't sweat that actual amount of pressure, it is only about 2.5-3 pounds of pressure, as long as it is less than you used to create the burr, it's fine. It is your knowledge that these actions are "cleaning the edge" that will guide you. Naturally you are not going to just keep pressing down as hard as you did before. This stage proceeds a lot faster than your initial burr forming stage. (This is where I changed my technique, before, once the burr was created I moved to a finer stone and then went to work with less pressure. However, I found that doing this on the same coarse stone improved the degree of sharpness, the results have always been better.)

   It is very very important to realise that you do not want to over do the pressure here, you are using a coarse stone, the burr is formed, metal that had to go has gone, so too much pressure at this stage just keeps forming a burr and thus removing metal that you don't want to remove. So limiting pressure here is key to this stage, think cleaning, not grinding. So if you started with a 150 grit stone for example, you may want to move on to a less coarse stone before continuing after the burr formation. I don't, but I am very aware what this coarse stone is capable of so I just reduce the pressure even more.

Update:  A friend asked a question on my P3 pressure, basically asking if I really use P3 pressure on the 1k and above stones, is that much pressure necessary?
It's a good question but I have to emphasize that my P3 pressure is really just half of the pressure I started with, perhaps calling it P2.5 pressure is more accurate.  I think is important not to use enough pressure that will raise a burr and this can be tricky so when I am at this stage, I am constantly checking for a burr and there are times when I can feel the most subtle one forming so at that stage I immediately reduce pressure. Remember that your edge at this stage is very very fine so it will be easy to form another burr. It is not the end of the world of course, as long as you are vigilant and take the necessary steps to ensure that your burr is completely gone when done, you are doing well. 

 (The other thing to note here is that if you did use a 150-220 grit stone for example to start the process, your initial P4 pressure can be a little less than if you started with a 400-500 grit stone. That very coarse stone works more quickly, so less pressure is required.....start lightly and move up in pressure as required.) 

   Now we are getting somewhere, the knife is getting pretty sharp now and it's time to reduce the pressure even further.


        Now I go down to about 1 pound of pressure, it is very light as I continue my efforts to clean the edge and I am still on the first stone. This whole process from P3-P1 only takes a few minutes, I don't make a lot of passes on the coarse stone. I repeat the process of moving the knife over the stone at this very light pressure moving on the right side of the knife from tip to heel and then heel to tip then flipping the knife and starting at the top of the stone moving from heel to tip and tip to heel.  (This is the way I have always sharpened, if you start at the heel that is fine, same thing, I am not suggesting that you change your approach)

    By now I have completely relaxed my pressure and I am basically holding the knife stable and using the least amount of pressure to ensure the edge is moving over the stone properly, as it did in the previous stages, I am just cleaning now, avoiding grinding


   This is simply a stropping motion where I use trailing strokes only, 2-4 passes per side and I am extremely gentle here, I am almost lifting the edge off of the stone but not quite. 

    The work is now done on that first burr forming stone.  Since I always go from a coarse to a medium stone I will add some points here.  

   To be clear, a coarse stone in my mind is one that ranges from 150 to 1, 000. Now I know you can get stones down to 24 grit, for the purpose of my explanation I am starting at 150. Now, what about the 1,000, is that really a coarse stone?   Well, if it is all you have, it is, it is a beautiful blend of coarse and medium stones and you achieve this blend by manipulating pressure with the stone. 

     Now when I move to the next grit, remember, I have absolutely no need to ever use P4 pressure again on the same knife. So I start with P3 and work my way down to P1 pressure and now I am just refining, removing the scratches from the first stone. Since I am often at the 1k or 2k range here, I can increase the number of passes at the P2 and P1 level.  What I do is feel the edge after I have finished a few passes at the P2 level and if it isn't quite sharp enough for me I just do a few more passes.

I hate to say "Make 2 passes per side" I don't want to get to the point where I am counting, that's boring, I just make "a few passes" and continuously feel the edge and look at my work.  Then,  when I move to the final P1 pressure, I can do the same, at this stage the pressure is so light that I am really just cleaning the edge. (I have a lot of time under my belt at this so if you are having problems with varying the pressure and still maintaining control, don't over do it, don't continue to grind until you can do this  with the absolute minimal amount of pressure).

An axe I played around with, I don't do axes. 

  Remember please that this is just the way I sharpen a knife, it is not the only way of course and I am not, and never will suggest that you stop what you are doing and do this. I am just sharing what I found works for me.  If you are reading this and thinking that I am out to lunch, I really don't care, you keep doing what you do, maybe it is even better than this :)

    Also you can be assured that my opinion is unbiased, I am not trying to sell you anything, use whatever it is you are using now. 

   Thanks for reading and don't hesitate to ask questions if I have missed something or left something less than crystal clear.


Here is the updated version of the pressure video.

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