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The Mechanical Properties of Wood - Application to Axe Handles

From the title of this post, you should suspect that I'm going to focus on wood handles, and I will save composite handles for another post. There is some overlap between the two, like how in a wood handle a continuous straight grain makes the handle stronger than a discontinuous grain, and similarly in a composite handle, straight continuous fibers (usually fiberglass) will be stronger than discontinuous (short/chopped) fibers.

An axe handle should be split from a stave (a narrow piece of “raw” wood) instead of cut out of a board. The grain of the wood should be continuous from end to end, or the shock from use will cause the handle to break apart (think baseball bat). Long, straight-grained woods such as hickory or ash are traditionally chosen for axe handles because they are strong and produce long, straight staves, and they have good mechanical material properties, like many other hardwoods. An axe handle should be from a log that is straight, without twists, branches, or burls, and that hasn’t been cut into firewood. If possible, it should be from the low part of a tree trunk, as trunks tend to be straighter closer to the ground.

I mentioned the good mechanical properties of ash and hickory, but you don't have to take my word for it, because there are wood scientists and engineers that have studied the properties of wood in depth. The Wood Handbook is a fantastic resource for engineering data on the different types of wood, the effect of grain orientation on the material properties (wood is orthotropic, which is just a fancy way of saying that it's properties are different in the grain direction from the properties across the grain direction, i.e. wood is stronger along the grain - but you already knew that). Here are some excerpts from the tables on mechanical properties - In every column, a higher number is better, except for specific gravity (density) since ideally, wood should be super strong and super light (but its not, so I guess that's why we make aircraft from carbon fiber instead of wood).





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