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Testing the Edge

I test an  edge by trying to cut copier paper.  I hold the paper in my left hand and let it hang down.  Then I push the edge of the blade into the edge of the paper.  The blade should cut the paper with almost no force.  I test several points along the blade's edge because it is very easy to have one part of the blade very sharp and another part not sharp at all.  Read more on sharpness testing.

My blade passed the test in this case, but I have sharpened plenty of times when it did not.  When it doesn't pass, I usually just spend some more time at the 0.5 micron abrasive and that fixes it up.  If that doesn't work, then here are some things I look for:
  • Did I raise a wire edge on the 40 micron abrasive?  That is not strictly necessary, but I have a much higher success rate when I do it.
  • Did I "dub" the edge?  If the abrasive is not glued down well, it can flap up and dull the edge.   I have to be particularly careful about this after cutting off part of the used abrasive.
  • Are the abrasives dull?  Sharp abrasives cut much faster than dull abrasives.
  • To help see the problem, I sometimes look at the blade under magnification.  I use a stereo microscope because I have it, but I have heard a jewelers loupe works well.
  • If all else fails, you might want to try sharpening a different blade.  I have at least one inexpensive chisel that will not pass the paper test, no matter now much I sharpen it. 
With a sharp edge, I'm ready to get to work!

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