What Thumbnails Are For

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Sharp makes everything better; less force is required to cut, control is gained, and the surface left from the tool is superior.  As obvious as that is, it is easily forgotten in the midst of a project and the haste to get to work.

I was reminded of this once again as I was paring the interior of this maple bowl a couple days ago.  I had been working for about ten minutes and the gouge was cutting, but maybe not as sweetly as I’d have liked.  The amount of effort required to propel a tool and the quality of the wood surface left behind provide feedback, but I also find a quick and simple test often helps to confirm suspicions of an edge in need of a touch-up.

I hold the gouge (or chisel, knife, axe…) very lightly and at a shallow angle to my thumbnail.  With just the slightest of pressure — no more than the weight of the tool, for most tools, less — the edge should bite instantly rather than slide down the thumbnail.  In the case of my gouge, only the wings of the edge bit instantly, the more-used middle portion slid.

Often, a bit of stropping is all it takes to get back to work.  But eventually the area near the very edge of the tool becomes too rounded.  You’ll find that the tool has to be raised to a much higher angle to get a good thumbnail bite.  So the thumbnail test not only tells you about the sharpness of the very edge, but also about the geometry near the edge.  It may tell you it is time for a touch up on a stone, as it did for me in this case.

Start at the far corner of the edge...

Start at the far corner of the edge…

...and slide the tool forward with the lightest pressure along the edge of the thumbnail. Obviously, avoid contact with any skin in front of the nail.

…and slide the tool forward with the lightest pressure along the edge of the thumbnail. Obviously, avoid contact with any skin in front of the nail.

Another thumbnail test involves running the edge of the tool very lightly along the end of the thumbnail.  I often do this test during the final stages of sharpening.  It will reveal even the slightest of nicks or wire-edge remnants.  It is amazing how something imperceptible to the naked eye can be revealed through a vibration transferred through the thumbnail.  This one might make observers cringe, but there is really no danger if you’re careful.

You might wonder why a thumbnail? Why not a scrap piece of wood, or something else not attached to your body?  What about my manicure?  I think the best answer is feel.  You feel the subtle bite not only with the hand holding the tool, but in the thumb as well.  You receive more information.  You will not end up with gouges in your thumbnail; the edge leaves just the slightest of nicks.  Plus, thumbnails just seem to be about the right hardness — and they’re always there when you need them!  I guess that’s what they’re there for.

 

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5 Responses to What Thumbnails Are For

  1. david os says:

    thanks for this.i also use this method particularly at the end of sharpening i feel it gives a far better response to where my edge is at as opposed to shaving hair on the arm .or looking for a white light along the cutting edge.love your work and enjoy reading your posts.thanks regards david.

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  2. Dave Fisher says:

    Glad to hear that. I confess, that I still can’t resist the arm-hair shaving test, but I, too, find the thumbnail test more telling. Doubtless, both have been around for millennia; Noah probably preferred the thumbnail test.

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  3. James Kuhn says:

    Dave, Happy Holidays to you and your family!! I use the ‘fingernail method’, too. If, I’m trying to explain how sharp one of my tools are to someone who is new to sharpening, I might demonstrate using the arm-hair popping method because it’s more visual.

    Unfortunately, after decades of sharpening, I still do not sharpen tools to my satisfaction. IMHO, my tools are just never sharp enough. Don’t get me wrong, they work, but I feel they could be sharper. I recently invested in a set of diamond Hones and have had decent results so far. The coarser grit has been useful in re-establishing a flatter edge profile on both my carving Axes. I use a combination of the diamond hones and wet/dry sand cloth to establish the edge. Then a final hone with Green Oxide.

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    • Cynthia Sartor says:

      I too have problems sharpening tools. I use a JoolTool for my gouges and it works wonders. I dont have a good means of sharpening my straight knives yet. I know what you mean, things are never sharp enough. Happy carving.

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      • Dave Fisher says:

        I know how you feel, James and Cynthia. I often get frustrated with sharpening. I’ve realized that I’ll never achieve a perfect edge, so I get it as best as I can, then get on with the carving. It’s easy for me, however, to get so caught up in the carving that I don’t stop and consider that it’s time for a touch up. It usually hits me when I need a running start to get the gouge to cut!

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