Knife sharpening

[Mike Fairleigh]

I have a question about setting the grinding angle when sharpening a knife.  My question would apply regardless of which knife jig is used.

The knife in question is a 7" survival knife similar to the one pictured.  The same question could apply to many types of knives.  Notice that each side of the blade consists of 3 surfaces - 1) the flat, unground surface near the rear edge or spine of the blade, 2) a wide relief grind that essentially turns the whole blade into a wedge, and 3) the actual edge grind (not really visible in this photo, but it is there and its a steeper angle than the relief grind).  When setting the grinding angle using the WM-200, which surface should be referenced?  The actual cutting edge is obviously too narrow to use, but the relief surface is a different (and unknown) angle.  I don't see any predictable, let alone repeatable, way to grind a known angle.

[Black Mamba]

You raise some of the concerns that I share. On many of my knives, the actual cutting edge is too small of an area to reliably establish the angle using the WM-200. I hope some of the folks who can enlighten us will chime in with their insight.

Tom

[Jeff Farris]

With a knife with a relief grind, set the AngleMaster to 25 degrees, rather than 20 and reference to the taper.

[Mike Fairleigh]

So you recommend a 40* included bevel (20* each side)?  Thanks Jeff.

[Herman Trivilino]

You have to reference to flat unground surface if you want to know the true angle of the bevel.  (Imagine a plane running through the center of the blade and passing through the cutting edge.  You measure the bevel angle relative to this plane.)

I think Jeff is assuming the relief grind is at an angle of 5 degrees.  So, if you follow his recommendation and set the angle master to 25, relative to the relief grind taper, you'll end up with a 20 degree bevel.

That is, 20 degrees on each side, for a total of 40 degrees.

If a knife is too small to reliably set the bevel angle, chances are it's too small for the knife jig.  In that case you have to sharpen it free hand, and just eye-ball the angle.  It's just a knife, precision's not that critical.  I can't really notice the difference in the way a knife behaves if I change the bevel by 5 degrees.  On a chisel, though, 5 degrees makes a big difference in the way the chisel behaves.

[Mike Fairleigh]

Thanks Herman, yes, I understand bevels, included angles, etc.  I just wanted to clarify Jeff's statement since a 40* edge seems pretty steep, and wanted to be sure that's what he meant.  I might reduce the equation by 5* per side for the knife in question.