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.