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Sharpening Knives Using Sandpaper And Mousepad

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Sharpening knives using sandpaper and an old mousepad is perhaps the cheapest and one of the most effective sharpening systems you could make at home. Somehow, it's very overlooked and you don't hear much about it, except for the knife related forums. I mention this method all over the place in my knife reviews, and occasionally someone asks what do I mean anyway. So, here it is, more or less detailed description of the magic sandpaper/mousepad combo and couple other tricks to make your sharpening job easier.

    Major pros for this system include:
  • Very low initial cost, most likely you have more than one used mousepads at home, so all you have to do is get a few sheets of sandpaper and you're ready to sharpen;
  • Another very important advantage of this setup is its forgiveness with the consistency of the edge angle. For the beginners with free hand sharpening, the major obstacle is the consistency, i.e. the consistent angle between the knife and the sharpening surface. Because mousepad is soft it allows for greater margin of error compared to sharpening stones;
  • Resulting edge is very well defined convex edge, which is better compared to standard V edges in many aspects, including durability and cutting performance for the given angle;
    What you will need:
  • Mousepad with the flat surface, I emphasize flat, since there are some weird things with all the bumps and grooves. Forget those, simple flat pad, just not too soft; Alternatively, you could use a thick leather surface, like the honing pad, top of the picture.
  • Sandpaper of various grits, details below;
  • Magic marker or whatever marker, this is optional, but helps a lot;
  • A few quarters to help you keep the consistent angle;

Setup

- Setting up the system is very simple, just put the sandpaper on the mousepad and you're ready to go. Preferably you cut mousepad into suitable size rectangle. Obviously you need to use some method to make sandpaper stay in place during the sharpening process. Simples is to buy sandpaper with sticky backside. Alternatively you can fold sandpaper over mouse pad and use duct tape or something like that.

Sharpening

- Also very simple. You use trailing strokes, don't push the edge into the sandpaper, pull the edge with the spine leading. The rest is as with usual sharpening process. You have to raise the burr on both sides of the edge if you're sharpening the double bevel edge, after that you switch to higher grit sandpaper, or if you're done then proceed with leather strops.

I've experimented with different techniques using this setup. Not so sure about coarse sandpaper, but whenever I use fine microabrasive films, anything from 15µm down to 0.3µm, I use back and forth motion on the block. I don't use high pressure and I guess because of that I can use both, forward and trailing strokes. Coarser sandpaper has more drag and resistance to it, so it'd get cut or damage the edge, but with high grit abrasives both, push and pull work, at least in my experience.

Magic Marker

- Remember I mentioned above, optional magic marker might become handy? Here's why. If you need to match existing edge or let's say you are trying to continue on the interrupted sharpening, then paint only the edge with the marker and make one or two passes on the sandpaper. if your holding angle is correct marker will be gone from the edge. Too high and marker stays at the shoulder of the edge, too low and marker stays on the edge tip. Simple, right?

Knife Edge Sharpening Angle Calculation

Coins

- First time I've heard about coins was from Japanese makers, when they measured edge angle in coins. It's pretty simple and quite helpful, especially for the novices. Basically it tells you how many coins you have to stack up to get the desired angle when you raise the knife spine to that height. Don't know what Japanese coins are in terms of thickness, but US quarter is 1.75mm (0.069"). The simple solution is to stack up necessary number of coins and put them on the sharpener surface, closer to the end, then raise the blade spine, so that the lower side matches the coin stack height and use it as a reference during the sharpening. If you want the precise angle calculation then you need some trigonometry, which is very simple. the angle is arcsin(coinheight/bladewidth), where arcsin is inverse function of sinus. If you want to be very precise then you'd have to take into account blade thickness. The diagram attached here explains why precise angle calculation requires matching the spine center and not the lower edge of the spine.