Posts tagged #broken axe handle

Axe Handle Breakage, Designing For Resiliency, Weak Links and Stress Distribution

An axe head with a wooden handle has some inherent problems. The head and handle are made of very different materials that behave differently. Steel has a very high density compared to wood. Wood is much more flexible than steel and will dent and break more easily. When using an axe, these differences can cause problems, such as the wood being damaged by forceful contact with the hard unyielding metal head, or the relatively high density of the steel head behaving differently than the handle, thereby putting stresses on the weaker wood. Breakage just below the eye is a very common occurrence. This article and video are an attempt to explain some common reasons why axes frequently break near the eye, having to do with design, or perhaps lack of design in some cases. Breakage in the main body of the handle can of course also occur, but I’m not really dealing with that here. I’m pretty sure that the greater percentage of axe handle breakages are initiated right where the handle meets the bottom of the eye, or within the first few inches of handle, especially if the breakage is not due to wonky grain or other defects. Shear stresses seem to be particularly high in this part of the handle.

In this article, I will be assuming that we are dealing mostly with American axe head patterns, which tend to have thinner eyes than European and Scandinavian axes. Even though American axe styles migrated back to Europe (many axe patterns on that side of the pond are actually American or modified American patterns) the axe eye sizes largely remained bigger than American axe eyes. This is an important point when we look at overall handle design, because with any given axe head, the eye shape just is what it is, and the size and shape of the wood where it enters the eye is therefore pre-determined. Some of these problems are obviated by the use of tapered axe eyes, in which the handle feeds in from the top and fits by friction, but that is a separate subject also. The assumption here is that we are dealing with American style patterns that are wedged from the top. For whatever mix of cultural and practical reasons, these axes have pushed the limits of strength and resilience of the wood used in handles, by evolving toward a small eye.

Aside from the size of the axe eye being fixed, there are two other things that are pretty much givens as well.

One is that the section of handle just below the eye, lengthwise (poll to blade) is wider than the rest of the handle. If the whole handle was the same front to back dimension as the eye length, it would be unusable, so the body of the haft has to slim down soon after leaving the eye.

Predetermined factor number two is that we need a slight flair in handle thickness just below the eye at the back of the handle, as well as on both sides, so that the head seats firmly around the bottom as it is driven on. The front edge of the handle can come straight out of the eye if desired, with no rise, but the other three sides need at least some flair, though not very much. In my view, it is always unnecessary, and also a detriment, to come out of the front of the eye and then immediately outward, forming a shoulder. I see no reason to do that, and every reason not to. If the handle isn’t completely straight coming out of the front of the eye, the rise is best made as a gentle transition.

WE CAN CONSCIOUSLY WORK AROUND THESE FIXED PARAMETERS. IN OTHER WORDS, DESIGN AROUND THE THINGS WE CAN’T CHANGE.

A Few Common Axe Handle Mistakes and What to Do About Them

On a recent snowy morning I answered a YouTube comment on axe handle breakage that led to a one take video shoot with a beautiful snowy background. Being conceived and shot in one morning, this is just a partial snapshot of the subject. It revolves around the specific problem of design factors contributing to handle breakage just below the axe eye. It could easily have snowballed into a multi-part series on axe handle function and design ideas, leading to yet another video or series on user contributions to breakage; but the snow melted and I couldn't throw out that beautiful backdrop, which some people actually thought was done with a green screen!

This is viewed primarily from the perspective of American axes, which are evolved in the direction of high performance with the consequence of increased delicacy. At least that is my current take on it. An axe is a system composed of a handle and head which creates some inherent problems. In America, the European axe systems that migrated here with early colonists eventually evolved toward higher performance creating narrower eyes that are inherently weaker than the wider ones they descended from. European axe eyes seem to have remained wider for the most part, often even when copying American patterns. In fact, I think the standard American axes are refined to a point where the handles could not be much thinner at the eye without becoming impractical for use with wooden handles, and some might argue that they already have become too thin. That is a subject for another time though. For now we will just look at, common problems that we see from both manufacturers and folks producing handles at home, which are easy enough to fix with some tuning up.

While there are a lot of people that understand some of this intuitively and practice it, I don't recall seeing it spelled out anywhere. It is my hope that this information will spread and eventually reach manufacturers, many of whom who are clearly not axe users. Most axe handles will need work out of the factory and that is fine, but the mistakes that are greater in concept and scale are costing a lot of handle breakages at the eye that are totally unnecessary. The essential problem is that manufacturers think they can just increase the thickness of the handle body to decrease handle breakage. When viewed as a dynamic system though, it quickly becomes obvious that doing so puts undue stress on the thin eye portion of the axe, instead of sharing the stress across the length of the handle. At some point, continuing to thin a handle will obviously reverse that problem and create excessive vulnerability in the handle's main body. That is really another level of this discussion though and one I purposefully avoided in this presentation. Another issue is that there are other types of stress that are incurred from different types of use or mishap that may be more likely to break the body of the handle. The grain of the wood and it's character is also at play. We are dealing with a tool that sees different types of stress at different times, has inherent problems that are not entirely solvable and involves an inconsistent natural material. Wood of even the best quality has fatal faults. We continue to use it for the same type of reasons I continue to use vacuum tubes in my stereo and guitar amps, and that is user experience. I personally also like wood because I can cut down a tree and make a new handle without relying on industrially produced products that I have to buy.

There is a lot of forgiving grey area in this problem and we don't have to engineer a perfect handle. But, we do need to avoid the largest mistakes being made and if we get a handle that has them, we can tune those problems down until we have something that is more comfortable to use for long periods of time and also reduces stress on the eye. I don't think I've seen a handle yet where the problem encountered was too little wood to work with!

Enough said here. While this video is incomplete, it presents some ideas that I think are important and which can go a long way toward practical solutions.