Wednesday, 13 February 2019

Pressure redefinined.

Random shots

     Thank you for being here. If you have followed by Blog you will know that I rely heavily on manipulating pressure when I sharpen, it's important to me but I want to make sure the reason it is important is clear. I am also acutely aware that this is not something new, I'm sure most freehand sharpeners utilize pressure, they adjust it as required, I am not trying to claim something that I have invented, just making things clear.

     I think it is important to keep the elements of the sharpening process as simple as we can, sharpening freehand and doing it very well isn't easy but it doesn't have to be complicated. The hard parts should become easier with practice, they will become easier. I want to keep the pressure process I use as simple as I can. Not that I think it is hard to understand but to a novice, with a lot of things to remember, it could be a small hurdle to overcome.

    I use pressure the way that I do, and maybe the way you do to achieve as clean an edge as possible, at the end of the day, when I put the knife down, I want that edge to be as free of any metal debris, burr as possible. That is to say, as clean as my skills allow it to be. Some say it can never be completely free of metal, you can't remove the burr completely. I don't think that is important to worry about, we can certainly get it pretty damn close, definitely free of any residual burr that we can detect without using extreme magnification. I can't see or feel any burr at all so I'm good with that.

    I use four levels of pressure but lets simplify that, we can reduce it to Burr Forming Pressure and Burr Removal Pressure.

     BFP is whatever you need to use to form the burr, the actual level of pressure used could be different with each knife, the steel, the condition of the edge, the stone used and the users skill level will all influence the formation of the burr but in every case, you need to use a certain level of pressure to abrade the steel, to remove the fatigued metal and expose the fresh new steel underneath. Now if I start with a 120 grit stone, I will use less pressure than if I started with a 500 grit stone but again, it depends on how resistant the steel is to abrasives. Hard Japanese knives with their superior steel are easy to sharpen, burr formation can be rapid but there is still a level of pressure required.

     Once I form the burr using the heaviest level of pressure that I will ever use on one knife (it may not be heavy pressure at all but it's the most I will use) I drop that level of pressure by at least 50% and I mean at least 50 percent. 

     Now I am into BRP (Burr Removal Pressure) and I will remain at BFP until I am done. I do not want to form any more burrs, now it is all about refinement and I begin that using the same coarse stone that I started with. 

     This is where several years ago I changed things up and that change has made a dramatic improvement in my edges. I used to switch from a coarse to medium stone after burr formation and relied on finer grit stones to finish the job, to remove the burr. 

   That coarse stone still has a lot to offer, coarse stones are fantastic and we can squeeze every ounce of goodness out of them by just reducing the pressure, significantly. I just use ever diminishing levels of pressure until the edge is a clean as I can possibly make it and the knife will be deliciously sharp when done. I strive to make the knife as sharp as I can on the coarse stone 

    The picture above depicts the light test that I conduct on every knife before I move onto the next stone. ( I only do it on the coarse stone) The shot of the left is a picture of a knife that I thought was done, I've used my various levels of pressure but I can still see light reflecting off of the metal that I failed to remove. Yes, I could just let my medium stones finish the job but why?. Why not get everything I can out of that first stone, so if I do see light at all, and it is hard to spot sometimes, I just go back to sharpening at a very light level of pressure, same coarse stone until I see no light at all, like the picture on the right.

     I know people use a cork and run the edge over it to check and remove tiny bits of metal that still remain, clinging to the mother ship. That idea always seemed counter productive to me, I can't stand to run the edge over a cork so I just use pressure in a few different ways to clean and sharpen the knife.

     Now when I move from this coarse stone to a 1,000 grit stone for example, the knife is already nice and sharp, I've set the stage for success by following my very simple rules and I continue to refine, sharpen and have a heck of a lot of fun doing it.

 So, basically its moderate to heavy pressure to form the burr (both sides, and as subtle as you can) and then it's just reductions in pressure until the knife is almost falling out of your hand.

Thank you for stopping by and reading this.
Peter Nowlan