Tuesday, February 11, 2014

On Handle Diameter Shape

I have found a lot written about axe handles on the internet these days, especially posts about grain orientation.  For example, British blacksmith Nick Westermann recently wrote a great series on axe handle grain orientation on his blog.  What is less available, it seems, is information on handle geometry, and specifically handle diameter shape.

Last summer I bought a beautiful adze blade from Kestrel Tools, and decided to make my own haft.

Part of the trick with these adzes is they need to be thin in the upper portion of the handle to lend a "springy" feeling to the adze.  In order to thin out the upper portion of handle, I removed material on the "leading edge," or "x axis", ie. the edge just below the acute angle.  To be clear, when swinging the adze the direction of travel is the "x axis" of the handle's diameter.  At a right angle to this is the "y axis."  So, what I was removing was material from the x axis, making the diameter along the x axis shorter than the diameter along the y axis.

Clear as mud?

Once finished with the adze, I merrily tied the iron on and went about chopping at some wood.  But the experience was positively scary.  The adze wanted to "wiggle" as I swung it.  Yikes!  Because the handle diameter was wider in the y than the x axis, it wanted to pivot in mid stroke to bring the long edge in line with the travel of the blow.  Not sure if I have described that clearly, but boy did the principle become plain as day when I swung the darn thing.

So, handle diameters have to be wider in the x axis than in the y if you want to control the flight of the blade.

Unfortunately, this lesson did not sink in until recently.

A week ago I was doing something awful with my Gransfors carving axe (using it as a wedge to split a round of apple wood that was way too large).  The axe head augured in and would not budge.  I had to beat on the head with a log to dislodge it, and after a while the handle broke.  DOH!  So stupid.  Lesson: use wedges!  Anyway, while making a new handle for the axe I ran across the same problem as my first adze haft described above.  I was shaping the curve of the handle and removing material largely from the x axis so that the handle ended up with a basically round diameter shape.  And wouldn't you know it, on the first swing I could feel the axe wiggle in space just like my adze had!  Double DOH!  It takes me a while to learn these lessons.

But this all got me thinking that, if an axe or adze loses control if it is too large in the y axis, does it gain control the longer the x axis is?  Maybe on my next handle I will leave it a bit longer in the x axis than the original Gransfors handle and see if it improves handling and accuracy.

Oh, and one more thing I have noted: As you swing a tool, the centrifugal force wants to make your hand slip toward the end of the handle.  Thus, if a handle diameter decreases down toward the butt end of the handle, your hand will want to slip down the handle faster than you (I?) would like.  Thus the total diameter of a handle has to increase slightly (or at least remain the same) as you approach the butt end of the handle.  This mistake is pretty easy to make when you are refining the handle so that it feels "right" in your hand, not realizing that in doing so you are effectively shrinking the final diameter of the end of the handle.

This may be obvious to many of you, but since this is a novice's notebook, so I hope some will benefit.


  1. Thanks for being so willing to share your experiences, Eric. I guess in the Kestrel-style adze you want springiness, but not floppiness. Must be a fine line, and I've never tried that style myself. One thing to keep in mind with axe or adze handles it to avoid a perfect circular shape. the oval shape registers the tool in your hand each time and keeps it from turning. Of course, a typical handle should be comfortable to hold over its entire length to allow for choking up all the way to the head, unlike a Kestrel-style haft. Good luck with the handles. There are some great shots of Willie Sundquist's hand made handles in his new video.

    Dave Fisher

    1. Hey Dave,
      I like that phrase, "register in your hand." That is just it.
      The Kestrel adze shape is interesting, in that it needs to be longer in the y axis at the top of the handle (to give spring), and longer in the x axis at the butt end (to register in your hand.)
      Also, I remember when we were working this summer and you pointed out the internal bevel of the Kestrel adze, and how it made it harder to use for bowl carving. I was bummed, but you said no worries, it might be helpful for spoon carving and other applications. Well, you were right. Anytime I need to make a concave profile (like on the underside of the handle) I just bust out the Kestrel.
      I did, btw, get a nice Hans Karlsson bowl adze and gouge, and will be building a bowl horse this summer. I hope to start carving a few bowls, but I am still having lots of fun on the lathe, so I am torn. There is only so much time...

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  3. Hey Eric,

    Enjoying your blog, its really fun! I'm Charlie from Kestrel Tool, and I'm interested in this conversation. I also love carving bowls. The butt end of our adze hafts are a little bigger than the rest of the haft so that it stays in your hand, and also because your hand needs to be down there for working with our adzes. The all important 90 degree angle from the tip of the blade to just above your index finger is the secret to our adze's efficiency. The adze shouldn't really be springy, unless you're using a finishing adze, which actually does spring a tiny bit. I'd strongly recommend buying one of our 'roughed out' hafts (or a complete one if possible). It might help in your learning process, and is a pretty well priced option. But maybe you've got a finished one as well. Hopefully you received our Adze-n-ends booklet, as there is some good info in there as well. You gotta try one of our E-bend Crooked knives, if you haven't already. You'd love it for the kind of work you do.
    We've recently updated our website and now offer online ordering! woo hoo! www.kestreltool.com
    Happy carving!

    1. Wow. Thanks for taking the time with this, Charlie. I should have said that I did make another one and it works well. I use the adze these days for creating convex curves in spoons. Love it. I have seen the new site, and it looks great. Thanks again for your post.