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JOEL Joel's Blog

Feel The Burr


Feel The Burr 4The simplest way to sharpen something is to create a burr or wire edge and then gently remove it. What's left is a sharp edge. You can read step by step instructions for sharpening here. The question of the moment is how to find out if the edge is sharp and the wire edge has been completely removed. The simplest way to do this, a far more reliable method than using a microscope or anything - is to feel the edge of the blade from both sides. If both sides of the edge feel the same and equally sharp - sharp, the edge is sharp with no burr. Your fingers are incredible sensitive and can easily feel something as thin as a human hair or one sheet of paper on a table. The trick of course is training your fingers to feel the burr. Here is how you do it:

With the chisel held straight up, gently hold your finger straight against the blade and pull your figure slowly straight downward (top picture). If the blade is sharp and you have a light touch you will feel a sharp iron catch in the ridges of your fingerprints. A dull iron won't catch, and if there is a burr you will feel it or, at the very least, doing the test on both sides of the edge will feel differently. The close-up gives a slightly better view of how lightly the edge is dragging against the fingertip. Whatever you do - don't go side to side on an edge - you will slice your finger wide open. If you move your finger up against the iron, not down, it looks safer but far less information about the edge can be felt. Going in the direction of the arrow is perfectly safe as long as you use a very very light touch.

Then what you do is flip the iron over and do the same test on the bevel (last photo). When you chase a wire edge or burr the burr will flip over from side to side as it's abraded, when you can't feel a burr on either side of the edge, and both sides feel the same you are basically done.

If you follow our sharpening recommendations of stropping on a plain piece of leather you can feel, as you strop the edge getting less grabby and smoother, this is because the very last bits of the wire edge, that you can't see, and barely feel are being removed. At this stage a strop with honing compound on it will simply create more wire edge and should not be used.

It's a very simple technique, I urge you to try it but I must mention one warning. In theory it's trivial to do this, in practice it took me a little while to get a sense memory of what a really sharp edge is like. So initially you have to pay attention and practice. It's the best way I know of checking an edge, and far, far faster than figuring out where your microscope is and getting the light just right.
Feel The Burr 5
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09/01/2010 andrew sacco
learning a lot thanks
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The opinions expressed in this blog are those of the blog's author and guests and in no way reflect the views of Tools for Working Wood.