Woodworking

  • 08 Sep

    Wood Movement

    No, I am not speaking of a revolution here. Just the immutable fact that wood moves, and learning to be a woodworker means understanding this.

    Right now on youTube there is a young, blonde, Canadian woodworker (who interestingly calls himself Samurai Woodworker…). He’s jumping up and down and working himself into a lather about the idea that wood movement is myth, and we should all just pretend it’s not an issue. He then goes on to list a whole host of situations (outdoor furniture, furniture in badly heated homes, wood not well dried,etc.) where he graciously concedes that, OK, maybe it does move sometimes. I assume all the ranting is just to get more viewers, but I believe that kind of disinformation does not advance our cause.

    You can believe whomever you choose, but let’s just say that in more than 43 years of making handmade furniture, I have seen numerous examples of how foolish it is to not understand and design for your wood to expand and contract. I had my first tool box, built when I was about 20 years old, of maple and ebony and bronze, explode with a huge boom while I was sleeping. It was well-crafted, or so I thought, with frame-and-panel construction and it still sounded like a tree had fallen on the house.

    The problem in talking about wood movement is that it scares the Bejeezus out of so many woodworkers when they are starting out, as it seems so evil and mysterious. It is neither, but just as in every other aspect of life, a little knowledge goes a long way.

    Envision a piece of wood as a collection of straws. Imagine that a wooden board is a six-sided rectangular solid, with three “pairs” of surface.

    The end grain is represented by the open ends of the straws, and has many similar qualities. Moisture and nutrients pass along these “tubes” to sustain the tree. It also allows moisture to escape the end grain at a much faster rate than it does across its grain. 

    Therein lies the imbalance that dictates a woodworker need study their material.

    The amount of movement along the board- the length of the board in most cases is so minimal, that we rarely need to take it into consideration. Movement across the board is what does require planning. While our wood moves across the board in both width and thickness. The vast majority of wooden furniture is not much more than 8/4” or 2” thick. There is some movement there, but negligible. It is across the board, where the rubber hits the road. And when you start gluing up 30” or 40” wide tabletops? I’m sorry my young friend from north of the border, but this is where you are wrong.

    If you need more proof of our amazing material and its willfulness, I have read that in the time when the hoity-toity were prancing around in stone castles and a little remodeling was in order, the masons just stacked lumber between two walls and threw water on it. Don’t believe me? Note that little saplings can grow through stones, split rocks, and even perforate pavement. Nature will find a way, and this makes wood so wonderfully complex and interesting to work with.

    Okay, now that you are duly educated, relax and know that there is no shortage of manners in which to comfortably and effectively deal with this when designing/building a piece. The simplest is to make any large surfaces of plywood, which has its ornery-ness taken out by gluing multiple substrate veneers at right angles to each other. Easy, but many fine woodworkers want no part of man-made materials in their work. Another way then is to control and work with the wood movement rather than fight it.

    For cabinetry, the problem is most commonly in door panels, and Frame-and-panel construction was developed centuries ago to deal with wood movement. A fixed dimension frame with a wide panel snugly filling it, but not glued and with space for the panel to expand into. For furniture, which is most of my work, the issue is usually with wide table and desk tops. The method I most often employ is to attach (notice I very specifically did not say glue — do NOT glue it!)  a batten to the underside of your wide solid top. This is held in place by a mechanical piece –think wood screw — that draws the top down flat to the batten. However, and this is everything, the screw cannot pass through a round hole. When the top expands the screw would be locked in place by the small hole and would be in direct conflict with the movement of the wood. The hole bored for the shaft of the screw must be elongated into kind of a through mortise or slot. Then the tension of the screw head pulling against the threads hold the top flat, while the elongated holes allow the top to move across its width all the while resting comfortably.

    There are literally hundreds of other methods for allowing your wood to move through the seasons and across the centuries. Rather than think of this necessity as a burden, I enjoy making it a design consideration. If you have a chance to look at a few pictures of my work at ebanistaschool.com or www.jonathancohenfinewoodworking.com you will notice several examples of how this can be done. Don’t let the wood movement intimidate you, but use it as a creative advantage.

    By Jonathan Cohen Woodworking