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.

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