The other day I posted a photo of some oak I’d planed for a joined stool, and mentioned that it was too slow-growing for chair work. I didn’t explain why, so this post will look at how oak’s growth rate affects its strength. This notion applies to ring-porous woods like oak, ash and hickory. Those are the ones I have the most experience with. I’ve used other ring porous woods like catalpa and sassafrass for various things, but I think of them as too soft for much furniture – certainly for chair work.
THESE NOTES APPLY ONLY TO RING-POROUS WOODS – THINGS LIKE MAPLE, CHERRY, ETC DIFFER. I DON’T KNOW HOW TO EVALUATE THEIR STRENGTH. SOFTWOODS ARE ANOTHER WHOLE STORY. MY BAG IS OAK, SOME ASH, ETC.
Below is a piece of white ash (Fraxinus americana) – each growth ring has two sections; the early wood/spring wood is the open porous bits. Then the latewood/summer wood is more dense. Generally the spring wood is the same size in each ring – the summer wood can vary from year to year, depending on various factors – light, water/nutrients, competition and more.
Next photo is of two boards I’ve kept as samples to illustrate this concept for maybe 20 years. On the top is a fast-growing red oak; the bottom board is the slow-growing example. (these boards are in the opening view of this post too). Both came from southeastern Massachusetts, both are 6″ wide. One has about 13 or 14 rings, the other over 90. It becomes hard to see them near the right-hand edge.
For my joinery work, like this chest, I prefer the slow-growing wood. It’s much easier to plane and carve. The way the chest is constructed the lesser strength is not an issue. The stiles (corner posts) are nearly 2″ thick x 3 1/2″ wide, the rails are 1 1/4″ x 4″ or so. Drawbored mortise & tenons throughout. So no problem.
For this sort of chair – same story – huge parts, 2″ thick posts, 1 3/4″ thick seat rails. Slow-growing ash is fine for this.
But if you want to make a light but strong ladderback chair, like those I learned from Jennie Alexander and Drew Langsner – that stuff won’t work. The rungs on this chair are just over 5/8″ in diameter. The posts on mine are about 1 3/8″ thick – Alexander’s were thinner. So this is a case where you have to be sure your material is up for the stress placed upon it.
Here’s another end grain shot, of two green chair rungs I shaved very quickly this morning. The one on the left is that new log, 12 growth rings to the inch – deemed useless for chair making, but ideal for joiner’s work. On the right is something I pulled from the firewood pile – 6 growth rings to the inch. How nice that they worked out 12 versus 6. Easy comparison.
I shot a 2-minute video showing how you can test your chair parts (or possible chair parts)
Below is a shot of those two rungs – the top one is the fast growing one that bent quite a ways before de-laminating – if I had shaved it more carefully, it might have bent without its fibers pulling up like that. Then the bottom two sections are the shattered rung. On the bottom view you can see the year-by-year fracture.
Bruce Hoadley’s book Understanding Wood: A Craftsman’s Guide to Wood Technology is where I go to read about what wood is doing & why. The updated edition is from 2000. I see it’s still in print from Taunton Press – or wherever you buy books.