Kyle Cameron 9/9/21 Kyle Cameron 9/9/21

Wood Movement Explained | A Beginner Woodworkers Guide

Introduction

As a woodworker I have been reading articles and listening to YouTube videos about what to consider when starting a new furniture project for what seems to be many years. One of the topics that I have known about and have neglected purposefully has been wood movement. I’m not entirely sure why I have ignored learning about it, maybe its because it seems like witchcraft to me, but I decided to sit down and research the topic to learn what exactly is worth knowing about the subject. In this article I explore what causes wood to move (i.e. cup, bow, twist, contract, expand), how wood actually moves, where wood movement tends to be most noticeable, and finally I will briefly discuss construction methods and provide some information to consider when dealing with wood movement in your projects.

What Causes Wood to Move

So, what causes wood to move? The most simplistic answer is moisture. Wood absorbs water and expels water throughout the seasons. Climate plays a huge role in this process. For instance, here is California where I live our climate isn’t overly humid. As a result, the amount of moisture fluctuation I notice in the wood I work with isn’t terribly noticeable. In contrast, states such as Florida, Louisiana, and Mississippi which tend to have the highest relative humidity levels in the United States, on average, will likely see the highest fluctuation in moisture absorption and expulsion in wood.

Why is this important to know? When you build a piece of furniture in your shop it is likely being built in a temperature and humidity-controlled environment. Once that piece of furniture is finished and moved to its new environment, into a home or even to an outside area, the moisture level in the wood is going to change. If you are building in an environment that isn’t temperature and humidity-controlled, then the same reaction will still occur. Let me be clear about one thing… there is absolutely nothing that you can do to prevent wood movement. Regardless of the precautions you take, the wood will take on and expel moisture throughout its existence. There are methods and processes that can be used to compensate for the movement, but you cannot stop it completely.

How Wood Moves

How wood moves is actually pretty simple. Wood moves very little with the grain but can move significantly across the grain. What does this mean? Trees grow outward from the center and in the process create growth rings. When a piece of lumber takes on moisture those rings will swell and when the piece of lumber releases moisture the rings will shrink. If you have a piece of lumber that is 10ft long and 8in wide you will see the board move across its width but very little to no movement over the 10ft length.

Wood expansion and contraction will follow the direction of the growth rings. Depending on how the tree is milled and where within the tree’s trunk the board is cut from you will see different types of movement. On a very basic level you have two types of milling techniques, flat sawn and quarter sawn. I am not going to dive into what these techniques are, they are outside the scope of this article, but quarter sawn is much more predictable in its movement. Quarter sawn lumber tends to stay much flatter and is much more resistant to wood movement than flat sawn lumber. Flat sawn wood can experience cupping, twisting, bowing, and other shapes that have no name… more witchcraft. Over time flat sawn lumber can deform to the point that the piece of furniture is unusable if the woods movement wasn’t considered when it was being built. This is seen in quarter sawn wood as well, but the effects are much less dramatic.

Where Is Wood Movement the Most Noticeable in Furniture?

There are a handful of common joints and furniture components that are more likely to experience negative effects if wood movement isn’t considered. Among the most common are tabletops (with and without breadboard ends), door panels, inlays, and exposed joinery (dovetails, finger joints, and through tenons).

Tabletops and Breadboard Ends

A tabletop will expand and contract over time resulting in uneven surfaces or delamination’s of the glue joints if wood expansion isn’t considered. This is usually compensated for by using tabletop anchors that allow the top to float over the table stretchers as the seasons pass. If your project incorporates a breadboard end then you should consider utilizing elongated dowel holes and plugs as well as a floating tenon design. These techniques will, in most cases, prevent catastrophic failures in your tabletop’s joints and surface, otherwise you will likely see those delamination’s and even large cracks occur.

Door Panels

In the case of rail and stile door panels, the panel is typically placed between the rail and stiles (frame), without gluing it or fixing it in place with a fastener. This is known as letting it float. In addition, the door panel is slightly undersized, which allows it to expand and contract within the frame. Rail and stile doors are constructed using these methods because, over time, the panel is going to move. If the panel doesn’t have the ability to expand and contract you may see failures in the frames joints and the panel may buckle.

Inlays and Exposed Joinery

There’s not much you can do to compensate for the effects expansion and contraction has on inlays and exposed joinery. What you are likely to see, with both, is raising and sinking of the inlay or joint as it relates to the surface it is recessed into or protruding from. That was a convoluted sentence but essentially, over time, as you run your fingers over the inlay or joinery you will feel them either sitting below the surface or slightly proud of it. In both casaes there isn’t anything you can do to counteract the effects. This is more of a good thing to know rather than something that’s going to cause negative outcomes for your furniture piece.

How To Deal with Wood Movement

Knowing that there is nothing to be done about preventing wood from moving, how do you deal with it? This next section is not going to cover any specific processes, because the topics are all individually lengthy ones. However, I will touch on some things to consider when purchasing wood and construction methods you might want to research a little more.

First and foremost, buy quarter sawn wood if you can find it. If the supply is limited in your area, attempt to purchase quarter sawn wood for elements of your furniture such as table stretchers, legs, door panels, and other similar pieces. The rest of your piece can be flat sawn if necessary. Apply a durable finish to your furniture pieces. The finish you apply will help slow how moisture is absorbed and lost by the wood. It won’t stop it completely but it helps. Spend some time researching the seasonal weather in your area and learn which parts of the year are the driest and most humid. Knowing this will allow you to construct your furniture pieces in a way that accounts for expansion and contraction in the best way possible. For example, if the time of year is exceptionally dry, make sure to leave plenty of room for expansion in areas of your projects that are likely to experience it. In the case of tabletops, use anchors that will allow your top to float while expanding and contracting with the seasons. With door panels, avoid gluing them into the rail and stile frame and provide a little space across its width to expand and contract. Last but not least, allow green lumber to dry sufficiently. Wood that has been freshly cut or milled from a log is going to have a high moisture content if that log was recently felled. In general, you want wood you work with to have about an 8 – 10% moisture level before working it. Depending on the thickness of the wood this could take months or even years to achieve, unless you have it dried in a kiln.

Conclusion

The moral of the story here is that wood will move no matter what you do to prevent it. Trying to restrict wood movement will likely create problems in your projects that will ultimately render your furniture unusable or in a state of disrepair that makes you cringe every time you look at it. It’s a far better idea to build your furniture, or woodworking project in general, to accommodate for wood movement. Doing so will make the longevity of your woodworking projects increase and they will likely last for generations. As is the truth for most things in life, it is better to be proactive rather than reactive. It’s a far better idea to build something the right way rather than have to deal with the consequences of poor construction.