Understanding Material and Joint Strength

Guaranteed Success Can Be Bad

Being scared of failing can steer us towards taking extra precautions to better the odds of success. It makes perfect sense, but it’s a shame because when things are over-designed and over-built, we often do not have the opportunity to observe the actual strengths of the components involved.

Ash Chair Prototype

Understand the Materials, Techniques, and Tools You Use

Forget cosmetic appearance – the real beauty comes from the strength within. The true beauty of ash, despite its strong grain lines, is its strength and flexibility. These physical properties allow components made from it to be shaped more aggressively. Likewise, fine-grained hardwoods allow us to cut finer details, including joinery and carvings. For these reasons, it is important that the maker have a good understanding of materials when matching them to the design.

Cribbage Table 1

I made a series of stopped cuts in the stretcher of “Beware of Step 27”, then wedged the sections apart and drove them into mortises in the legs.

Learn By Doing

As with most things, you can learn about things including the physical properties of materials, and strengths of different joints from books. It’s an excellent place to start, but a terrible place to finish. Books and pictures do not adequately convey the strength of a certain material or joint. Descriptions such as “good load strength and medium hardness”, or “an excellent joint for a drawer” do not actually tell you how it will fare in the real world. Videos are slightly better, but are still a poor replacement for hand-on experience.

Seek Failure and Learn

The best way to learn is to experiment yourself. Seek failure. Here’s a simple exercise I use to learn the strength of the materials I use. A project always yields some offcuts. Instead of cutting over-length offcuts to fit in the firewood box, I first try to break them.

Small pieces, I may try to fold with just my upper body strength, larger ones I may try to break over my knee. But for most offcuts, I set one end on the ground and the other on a block of wood, then stomp on it. It is impressive how strong wood is. Quite often, the wood will kink or bend before it fails.

Apply Your Knowledge to Your Designs

We can apply our knowledge of the materials and joints we use to the things we build. Remember that in most projects, the piece of wood taking load, whether it be a table top, chair stretcher, or drawer bottom is wider if not thicker too, and is hopefully not the subject of somebody stomping on it, trying to break it.

I think that this exercise will build your confidence in material strength, and possibly get you thinking about using materials in more daring ways.

One thought on “Understanding Material and Joint Strength

  1. Great post! I almost always bear my weight or overload by 50-100% on finished projects (as appropriate) as a final test and am amazed at how sturdy well made (or at least as well as I can) items are. Over time, like you suggest, I believe this has made my designs lighter as I find thinner and thinner material capable of still doing the job just fine (unless I’m just going for a heavier look.) Standard mass production component sizes have no doubt come to be from allowing grain run out & weaknesses, and inappropriate joinery. Eliminating these allows the materials to shine.
    BTW, I like your fan back chair. it looks very flexible and comfortable.

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