Posted by: woodbeecarver   in Knives

“Cutting Edge Sharp” refers to the end result of sharpening a knife blade by hand using various abrasive degrees of fineness and stropping on a leather strop to create the “true cutting edge.”  The drawing diagram  at the left (click to enlarge) of the “cross section of a blade being sharpened” describes what happens in the sharpening process. 

 For over thirty years I have been on the journey of continuing to learn the art of hand sharpening of knife blades.  The reason hand sharpening on various abrasive stones of decreasing fineness is used is because for this carver I have better control over creating a very sharp cutting edge.  The use of motorized sharpening systems can cause the uneven removal of too much of the blade making it smaller and smaller and create a wider bevel than I prefer.  Some carvers are very adapt at using power sharpening, but I prefer to do it by hand.

What I have discovered over the years of trial and error learning by doing is that sharpening the cutting edge of a carving knife is to produce cutting teeth along the cutting edge that are very much like the teeth on a saw.  It is these saw teeth that cut the wood fibers when the knife is used in a “slicing” action rather than a “wedge cut” when pushing the blade perpendicular into the wood.

  Shaping the sides of the blade to be flat from the top of the blade down to the cutting edge creates the secondary function of the blade that  “burnishes” the cut behind the “slicing action” of the cutting edge.  Sharpening this way creates a “micro” bevel which is thin enough yet strong enough to make very fine “slicing cuts” that glide the blade quickly to the “burnishing” sides of the blade to create a very “smooth and slick” surface to the wood, thus eliminating the need to do any sanding.  This method allows for very “clean” and “sharp” cuts to help establish “sharp details” in a carving.

Click on the photo above which will make the wording of the diagram readable and study the diagram.  The diagram shows the cross section of a blade being sharpened with the sides flattened from the top or back edge of the blade down to the cutting edge.  Find the line that says “True Edge” and right below is an enlarged section colored RED to indicate the “Wire Edge” and at the bottom of the “Wire Edge” is the “Burr Edge.”

In the sharpening process as the side of the blade is flattened when it gets flat enough a burr edge will appear along the cutting edge.  What is happening in the “RED” section  (greatly enlarged) in the diagram containing the “Wire Edge” and the “Burr Edge” is that the metal of the blade is being bent back and forth as the blade is sharpened on one side and then the other side.  As sharpening continues down to the finest abrasive and finally in the stropping action is that the “Wire Edge” and “Burr Edge” gets smaller as it continues to bend back and forth.

  Stropping must continue until the “Wire Edge” comes off the cutting edge like a “little wire” and the “burr edge” is totally removed.  One of my rules of sharpening is: “Sharp Can Be Sharper,” meaning that one should continue to strop long after it is thought the blade is sharp because it can get sharper.  What often happens when one stops too soon before the “Wire Edge” comes off is at the point of the “Burr Edge” it may appear to be sharp, can even shave hair off one’s arm and even peel a shaving off a piece of wood. 

 This is what is called a “False Edge” because a blade in this condition whenever it carves into the wood repeatedly, the edge will turn over.  When the edge turns over some think the blade is no good, that it has lost its temper and that it is a piece of junk.  What happened is the edge that turned over was actually the “Wire Edge” indicating that the sharpening process stopped too soon.  The goal is to continue sharpening until the “True Edge” is achieved with the removal of the “Wire Edge” with continued stropping to polish the cutting teeth of the “True Cutting Edge” to make the “CUTTING EDGE SHARP.”

This entry was posted on Tuesday, June 17th, 2008 at 10:19 am and is filed under Knives. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

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