Know the Strengths and Weaknesses of Your Materials

This photo in my Twitter feed caught my eye. It’s a long workpiece being supported by a custom-built support resting on top of a platform. The photo was taken by Dominic of Be Inspired With Dominic.

It may not seem noteworthy, and perhaps it is not worth a blog post, but I noticed that the material of each component is perfectly suited to the requirements of it. While I don’t think the requirements of the support are very demanding, I did find it interesting to analyze each component nonetheless.

Let’s examine the components in detail.

The top piece looks to be flat sawn pine, which means that the growth rings are orientated more or less parallel to the face. Since the majority of wood movement occurs in the direction of the growth rings, there will be a minimal change in thickness as the humidity changes.

Pine, as well as many other softwoods, has a distinct growth ring pattern. This is a result of different growth rates – early wood (the lighter coloured area) develops during the time of year that the tree is rapidly growing, and the late wood (the darker lines) develops when the tree grows more slowly. Late wood is denser, and if you’ve ever sanded or carved pine, you have experienced the difference.

In this application, with enough use, the pine board may start to wear and become uneven. The softer early wood would wear first, leaving ridges of late wood. I can’t decide whether this smaller surface area of harder material is a benefit or not. It would likely allow materials of equal or greater density to the late wood to slide over it easily, but may actually increase friction with softer materials that tend to bed into the stripes of late wood.

Moving on, the vertical riser appears to be an L-shaped assembly of K3 particle board. I usually see this low grade material used as warehouse shelves supported by metal crossbars, since it tends to sag under even its own weight and easily crumbles or breaks if load is applied without adequate support.

In this application, the particle board is primarily subjected to compression forces which it can easily withstand. There would also be some lateral forces applied to it from the friction of the material being pushed across the top of the support, but the L-shaped assembly should be more than adequate to resist those forces.

The base also appears to be K3 particle board. It is fully supported so sag or breakage while in use is unlikely. However, it may break if dropped or thrown. This is a good example of not overbuilding.

Most sheet goods are dimensionally stable if they stay dry, and K3 is no exception. The use of this material is unlikely to result in a significant change in dimension unless it gets quite wet from a leaking roof, hose, puddle, or other water source.

I don’t know how much time or thought Dominic put into designing the support and choosing materials, but it seems to me that he was able to build something that will serve him well for many years using scrap material with little or no value.

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