Wood movement can sound like an existential threat for someone getting started in woodworking.
The way people talk about it, you’d think a jewelry box might explode and level your shop.
I’m here to tell you, it’s going to be ok.
Wood movement is absolutely something to keep in mind, but it’s not an otherworldly force shrouded in mystery. No need to offer sacrifice to the wood gods.
In fact, I’m going to show you that wood movement is:
- Predictable
- Easy to calculate
- Not as bad as you think
All the information here is based on a 500 page handbook from the US Forest Service’s Forest Products Laboratory. It goes into painful detail on wood as an engineering material, using 30 years of data to boil wood movement down to a precise science.
Darryl Hopkins
January 23, 2023
OK, I think I answered my own question earlier. I was trying to interpret this message from the Wood Calculator page: “Best month to assemble project would be February as that would limit movement to +/- 0.05 (≈ 3/64) inch(es)” for a 15" wide cherry flatsawn wood panel.
Reading more carefully, I see “+/- ≈3/64 inches”. The key thing is the “plus or minus” which I overlooked earlier. I believe this means that on a typical day in February in my region, the piece of lumber is at the midpoint of its cyclical expansion/contraction cycle. In February, I can expect it to contract maybe another ≈3/64 and expand maybe another ≈3/64.
But if I’m making this object in the most humid month of September, which has the highest equilibrium moisture content (EMC) of wood in my region (Vermont), then I should expect very little to no additional expansion, and anticipate as much as 3/32" of contraction. And if I’m building in May, which has the lowest EMC, then I should anticipate no further contraction but expect as much as 3/32" of expansion.
I guess this is telling me that I shouldn’t procrastinate finishing my projects! Imagine staring a project in May and finishing in September. I’ve done that! My head hurts thinking about the wood movement considerations with such a timeline.