A Tip for Sharpening Marking Knives - Popular Woodworking Magazine
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“The more you sharpen the blade the more it deforms, and instead of a straight edge line, you end up with a concave curvature that develops towards the bolster.”

In my classes, we use marking/carving knives quite a lot. We score lines in preparation for making a “knife-wall”, we use them to whittle animals, to cut paper veneer and more.

Our knives are shaped in the traditional European pattern with a wide bolster at the meeting point of the blade and the handle. To sharpen a knife I use DMT diamond stones.  Typically, I begin with a fine stone and move on to extra fine and finish with a strop.

Over time, I noticed that the rims of the rectangular stones lose many of their micronic diamonds and cannot erode the blade efficiently. That caused a problem, which eventually alters the geometry of the blade. The more you sharpen the blade, the more it deforms and instead of a straight edge line, you end up with a concave curvature that develops towards the bolster. Curvature in a blade edge may not be that big of a deal if you are willing to spend the extra time and care to sharpen and hone it, including using round sharpening medium on the concave area. But attempting to achieve this solely on a flat diamond stone is problematic, and will eventually reduce the effective length of your cutting blade to only the straight portion of the edge.

A typical European style marking or carving knife has a wide bolster at the base of the blade.

But over time I noticed that the rims of the rectangular stones lose many of their micronic diamonds and cannot erode the blade efficiently in the area near the bolster.

My solution to this problem was to create a gullet at the meeting point of the blade and the bolster. This is not my innovation of course, it’s a geometry that I’ve seen in other knives – though much bigger. To create the gullet, one can offer the blade to a grinder and use the corner of the grinding wheel in order to cut into the steel. 

Another option is to use high-speed rotary tool equipped with a narrow cylindrical or conical grinding stone. And of course, there is the option of using a diamond file or sandpaper wrapped around a nail or a dowel.  

Once the gullet is created, sharpening becomes fast, easy and repeatable. It will ensure that every time you sharpen, you’ll get a long and uniform straight edge. Over time, you will need to revisit the gullet and deepen it, but that effort is well worth the time spend.

– Yoav Liberman

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Showing 7 comments
  • pop would

    The gullet or notch you describe is a common feature on pocket knife blades, undoubtedly for the same reason.

    • Yoav Liberman
      Yoav Liberman

      You are absolutely right. In fact Flexcut and some other North American manufacturer make this notch part and parcel of the knife. It is the Europeans that adhere to the no-notch design.

    • Sean N
      • Yoav Liberman
        Yoav Liberman

        Thanks so much for the link to the drawing and for sharing with us the right terminology.

  • OnTheCoast

    Very interesting idea. I will try it since I also worry about the edge of my leather strop. I wood carve, how do you maintain the angel of the blade? I try for 10-12.5 degrees, or imagine a US dime under the top of the blade. I would like some better tips! Thanks for all you articles, I am enjoying them.

    • Yoav Liberman
      Yoav Liberman

      Hi There,
      Thanks for the kind words.
      I sharpen and hone the blade somewhere between 10 and 15 degrease to the stone. Over the years I developed a muscle memory for this angle which I routinely use when sharpening our kitchen knifes. With practice I am sure that you will need the dime less and less, but as an angle set up guide I think it is a fantastic idea.
      Best,
      Yoav

  • Rob Porcaro

    Yoav,
    Makes good sense. Good tip. Got it. Thanks.
    Rob

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