Wood Movement

Article - September 15, 2008

This week’s question comes from Martin. Let’s see what he has to say: I’m a relative newcomer to woodworking and have been watching your podcasts for a month or so now and am finding them very interesting. One major point I have picked up on is how much attention needs to be paid to the way in which wood moves over time as this never really occurred to me before. I am currently working on my 2nd ever project which is a jewelry box which will hopefully be made out of a nice piece of cherry.
I have attached a couple images of what I’ve designed so far.

The problem I am stuck on is with regards to the top of the box. I have designed the box to have the top made out of two bits of cherry butted up against each other which will then sit in a rabbit around the top of the side pieces. From what I have seen online recently it looks like this could result in the top expanding and “popping” the dovetails out, or cracking the top piece. I’m pretty much at a loss as to how I could get around this and was wondering if you had any pointers.

And here was my response:
Hey Martin. I too was very surprised when I first learned that we have to account for wood movement. I remember thinking at the time, “Oh great! Something else to worry about!” lol. The interesting thing is there are always exceptions to the rules and there are nearly always workarounds. Depending on the size of this box, you may never really have a problem. Obviously the smaller it is, the less it will move. And with small jewelry boxes, you can usually break a lot of the movement rules. Now if this is a reasonably good size, you certainly might have issues, but then again, you might not. How much of a gambler are you? If you want to get a little more scientific about it, check out The Shrinkulator.

Now the safe thing to do would be to redesign the top a little. And by re-designing, you might turn this dilemma into a design opportunity. The most obvious option would be to make the top more like a frame and panel. So the two cherry pieces would be set into a groove that goes all the way around the inside perimeter of the lid. The panel would essentially float, and thus be allowed to move. But of course, this changes the look.

Now if you absolutely do not want a frame and panel look, then your only other “safe” option is plywood. You can fully surround a piece of ply in that situation and have no adverse effects. And based on this design, the ply edges would be completely concealed and no one would have any idea that it was a piece of plywood. In fact, that would be the way I would do it if I wanted to adhere to that specific design. Good luck!