Wood Movement

Richard Oedel replies: One of the advantages of being in a shop with 40 years of history, we have 40 years of test samples! We have 30˝ mahogany cross-grain samples from the 1980’s that are marked against plywood sticks, so that we can see the movement over long periods of time.

In thoroughly dry wood, we can see the wood expand and contact over 3/16˝ per foot from winter conditions to summer. Others less. Each year. Swell and contract, swell and contract.

It does get less over the years, but never goes away. We have a sample that shrank over 1/2˝ in the first year—it must have still been wet when we cut it—and then less over each succeeding year.

Attach tabletops to bases with something that moves as well—sloppy screw holes, figure-eight hardware or slots. Figure out where you want the top to expand from. For example, a bureau should have the back in one location, so screw it down tight in the back so the wood movement doesn’t push it away from the wall each season. Then all the other screws should allow movement.

Jon Siegel replies: Wood moves as a result of humidity changes. The amount of movement that results will be determined by factors such as the type of wood and how the wood is sawn (grain orientation). For example, oak moves about twice as much as mahogany and plain-sawn boards move about twice as much as quarter-sawn.

For a complete explanation of this subject, read Understanding Wood by R. Bruce Hoadley (Taunton Press), a book I recommend for every woodworker. There is one chapter on how and why wood moves and another on how to allow for it.