When chairmaker Chris Williams became concerned about brash wood, he devised a test to detect it. Put the stick up on blocks and whack it with a mallet.
Brash wood, which is very brittle, will usually snap in two.
I took Chris’s idea and expanded it. I now use “The Sledgehammer Test” to select wood for overall fitness for a high-stress application, such as a chair in a cowboy movie (surely all those chairs were made from brash wood). I perch a sample stick shaved down to the desired size on two 4x4s. Then I smack the middle of the stick with a metal mallet – hard.
- If a stick is brash, it will snap in two.
- If the grain runs out in the stick by more than a couple degrees, the board will crack along the grain.
- And if the species isn’t really up to the task at that size (1/4” balsa sticks), it will self-destruct in a variety of ways.
The results can be comical. Some woods are almost indestructible – a 1/2”-diameter x 26” straight-grain ash stick will bounce the mallet right back into your face. And I’ve been able to break 3” x 3” x 24″ sticks of brash red oak like they were Twix candy bars.
Today I started making an Irish chair out of some European oak. Some of the grain was dead-straight but had some small hairline cracks. Some pieces didn’t have cracks. So I cut some samples to 1-1/8” x 1-1/8” (the finished size in the chair) and hit them with a sledge. For fun, I also took some European oak that I used for the seat that had about 10° of grain runout. I knew it wouldn’t survive the sledge, but it makes for a good video.
You can see the results above.
I have found the Sledgehammer Test to also be an excellent teaching tool. I recently had five professional woodworkers in the shop, and I showed them how to pick and saw wood for chairs. After they selected the wood for their sticks, we submitted the sticks to the Sledgehammer Test. The woodworkers quickly picked up on what the words “dead-straight grain” mean.
I know this test isn’t scientific, but it is practical. Even the Forest Products Laboratory has tested woods for brashness with an impact test – so I don’t think it’s only an excuse to hit things with a sledge.
— Christopher Schwarz
P.S. Shameless plug: You can read more about the Sledgehammer Test and how to pick wood for chairs in “The Stick Chair Book.“