What is a burr? – part 1

Almost any discussion on knife sharpening will include the term “burr.”  Sometimes referring to the “raising of a burr” as an evaluative technique and sometimes referring to “removing the burr” as a finishing step.  Additionally, the terms “wire edge” and “foil edge’ are sometimes used as synonyms for a burr although they are typically associated with edge geometries created during the finishing stage.  By any description, the presence of a burr reduces the keenness of blade and is therefore critically important to understand.

The WIkipedia page provides a definition, more relevant to machining of metal than to honing; however, the phrase “unwanted piece of material” is a key point for this discussion.

Raising a burr is accomplished by repeated abrasion (honing) of one side of the blade.  The apex will bend (plastic flow) away from the surface of the hone and the burr will grow as material is abraded from the bevel face.

Edge view of a burr raised by repeated strokes of one side of the blade on a DMT 1200 diamond plate.

Edge view of a burr raised by repeated strokes of one side of the blade on a DMT 1200 diamond plate.  This burr is easily felt by brushing a finger across the edge.

Burr_07

A cross-section was cut into the edge through the burr.

Burr_08

Cross-section showing that the burr is tens of microns long and several microns thick. Note the accumulation of swarf on the side of the burr.

For comparison, below is an image of the same blade honed with alternating x-strokes on the same DMT1200 plate.

DMT1200_11

The apex formed by alternating x-strokes on a DMT 1200 diamond plate.

In this case, the burr does not “grow” enough during one stroke (approximately a four inch stroke with less than one pound of force) to project past the ideal apex.  In fact, a raised burr is never formed during typical straight razor honing with alternating, edge leading x-strokes on a hard surface.

In future posts, I will show that the formation (and removal) of burrs during the finishing stages of sharpening/honing/stropping is more complicated, but also much more interesting.

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3 responses to “What is a burr? – part 1

  1. Thanks for posting this! Can’t wait to see the follow up… This seems to be popping up in a few forums recently, what is the most efficient method of burr removal/minimization after you have one? 😉

    Like

  2. People will be pointing to this Blog for years to come to explain the “unseen”. The SEM is like magic. The esoteric revelations presented here have eluded generations of sharpeners, craftsman, journeymen, and apprentice. Can you image how many craftsman and artisans of the past “ages” dreamed of seeing the apex of the edge like this and never actually had the opportunity? It’s like we just entered a “new age of enlightenment” for blades of all kinds. I am “blown away” and honored to have the opportunity to read this and “See” these images. A picture truly speaks a thousand words. If you set out to change the world of knifes, I think you have accomplished your task. I will never look at sharpening the same way again. Bravo!

    Liked by 2 people

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