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.“
38 thoughts on “The Sledgehammer Test”
Great post! Oh… what’s that amazing music on your video!?!
“Old Regular Melody” (traditional) performed by Dan Gellert on the soundtrack for “Mountain Minor” (2020).
Speaking as someone who was actually trained in the scientific method, it IS scientific. Science doesn’t have to be conducted following a $$$$ grant for “Hitting Sticks with a Big Hammer and its Effect on the Mating Habits of Endangered Left-footed Weasels” and dutifully recorded by three indentured PHD candidates.
Why don’t you play some bagpipe music? it would be just as good for the background.
Well, I wanted people to watch the film all the way to the end….
Ouch. I like bagpipes.
The first five seconds, as the bagpiper is inhaling, are fantastic
John, you are losing the argument!
I was looking forward, some day, to the Anarchist’s Pipes. I wanted to make one some day. I suppose you could still do it as a plumbing book. Or home vasectomy manual.
One of my best friends through high school was a bagpipe student. And it scarred me for life (though I am 32 percent Scottish.)
Hi Chris, very interesting results, and I enjoyed the music.
Just one thing; in Australia we would probably call that a “club” or a “mash” hammer. We reserve the term sledgehammer for a considerably heavier, long handled hammer used with both hands.
My family uses a similar test for potential spouses by inviting them to a large family gathering. Some don’t survive the shock.
My brother should have done that
Fun and useful. Thank you. Concerning wood with pre-existing weaknesses, we are at the start of an epic supply of wood in the East from ash trees that are being killed by the emerald ash borer. Any thoughts on how much strength that wood will lose?
We have had to burn (for fuel) a LOT of ash unfortunately. A lot of the ash lumber in our area was harvested from trees that had been on the ground for a while. It was worthless for chairs, but fine for casework.
In general, stay away from the giant slabs if you need high-performance ash. Test the rest. There is still some fantastic ash out there, but also some rotted stuff.
Question, not a comment: Are there any clues from the appearance of the wood that are predictive of the outcome of the sledgehammer test? 2nd question, what website address belongs below? I don’t have a personal or business site.
I test all the oak that is fast growing. And I look for small cracks or shakes. If I see those physical characteristics, I test it.
You don’t need to enter a website address in the comment field. It is purely optional
So do you test each individual piece before using it in a chair, or do you only test pieces that you suspect have brash?
Cool video. Thanks for sharing.
It depends. If all the material is consistent, I might test some off cuts. If I’m not familiar with the material, I test it. And if I see any defects I test it.
For me, If you have to ask the question then you know the answer.
I wonder if he got the idea for the test from the comedian Gallagher.
Good thing he doesn’t make chairs out of watermelons.
Probably the only comedian with a “splash zone” at his shows
Great demonstration! Besides grain direction, does the appearance of the wood (before the sledge hammer test) give any predictive clues about the outcome of the sledgehammer test?
Learned something to day good advice thank you. Also don’t know if I would build stick chairs but have though about chairs for dinning table well your book help in that
Nice video–visuals and music. My wife pricked up her ears and smiled when I was watching Sledgehammer Test, the movie. She recognized the tune, from her experience playing Irish traditional music on flute, uilleann pipes, and concertina. Connections there I guess.
I hope this isn’t a stupid question but do you test all the parts of the chair or just the undercarriage parts?
I test parts that I am unsure about. Here are things that make me unsure:
If the wood is straight, heavy and sound, I simply use it without testing. If any of the above apply, I whack a few sticks to get some answers.
Hope this helps.
Ouch. I have used many sticks like the second one and thought that it would hold up.
Could someone explain the “10 degree runout”? I only see wavy grain that has a lot of fibers running from one end to the other…
With a ring-porous species, such as oak, there is a lot of visual information: the pores, the rings, the rays. It can be difficult at first to learn what to look at for “straight grain.”
When I look at this stick, I see the grain tilting 10° off the centerline axis of the stick (I measured it). If it were 0°, then the grain would be running from end to end with zero runout.
I could write 1,000 more words trying to explain how to look at it. But the best lesson is to saw up some sticks, hit them with a sledge and observe the results. When I do this with students, they become experts in less than an hour.
Sorry if this isn’t much help.
One hour of beating wood to become an expert sounds like a bargain to me in so many ways, thank you,
Going to try this on some horse chestnut, which everyone tells me is no use, while playing that tune (also known as ‘Lament for the Broken Chair’).
I know you typically deal with dried wood, but do you have any experience doing this on green wood? Does it still work or does the flexibility of green wood keep together parts that would fail if they were dry?
I have not performed this test with green wood. Only kiln-, vacuum- and air-dried wood. Sorry.
I am assuming you use the same pieces that you test – any surface damage from the sledge is removed when you shape the stick.
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