Question about wood movement

[Rick Reinsma]

Hi everyone,
Just wondered if any of you experienced wood expansion/contraction on any of you finished projects. I am always a little leary when making ,lets say a desk or 5 drawer dresser out of solid wood . What method do you use to attach your tops to the sides or the attachment of dust shelves or even perimeter edge moldings and still allow for movement?..Thanks

[Jim Becker]

Rick, there are lots of techniques you can use to accommodate wood movement in your projects...don't shy away from working with solid stock for that reason! Given there are many ways to do carcass construction, the specific treatments for such will vary. I have learned a lot from various Fine Woodworking articles (including those available on their online subscription service) and Taunton's books on both joinery and specific styles. For example, Chris Becksvoort uses a technique for applying a molding around the top of casework that involves a sliding dis-continuous dovetail on the side pieces. (That Thos Moser also uses). This allows the case to expand and contract without wrecking the molding which is cross-grain to the carcass on the sides. A similar technique can be used for dust frames by only gluing in the front and letting the back move in a sliding dovetail. Etc. Etc.

My suggestion is you feel free to ask specific "how should I handle this" questions as you plan for a project. That will get you ideas that fit the situation at-hand.

[Ian Abraham]

Rick, first you need to understand the wood movement, it will move across the grain ( a board will get wider or narrower). It wont move along the grain (the board wont get longer or shorter).
So when you build your solid wood dresser the sides, the bottom and top are all effectively in the same orientation. You can connect the top to the side anyway you want, if they expand, they will expand together, the joint stays intact, the dresser just grows 1/8" deeper.
Problem comes with the back... if you were to fix a solid panel to the back it would be cross grain to the top and bottom (assuming the grain is vertical). Now if the back expands 1/8" but the top doesn't stretch any longer, it will pull apart. :o
So you would either use plywood for the back or make it with T&G construction so it has expansion gaps.

Now with your table top you make an apron out of long grain wood, with legs attached. You can ignore the small areas of cross grain where aprons and legs meet, the movement there will be small and the joints will allow for it. But the top will be cross grain to one dimension of the apron. Now you could T&G the table top, but thats a bit too rustic, so normally the htop will be attached by some method that lets the top move a little. Slotted screw holes or similar are one way.

Now when you look at woodwork plans again you will see how they go to great pains to avoid this crossgrain situation except in small situations. So doors and panels get made as face frames to reduce movement. There are lots of ways you could build stuff wrong, but if you look at conventional building methods you will see that they incorporate wood movement into the design. If you want to design your own stuff from scratch you have to think of this too.

Cheers

Ian

[Matt Meiser]

I have one project where it has been noticable--an end table with breadboard ends. The breadboard ends were perfectly flush with the sides of the field when I built the table. Once inside the house which tends to be dry from the heat and A/C, the field shrank and the ends now stick out past the field maybe 1/16-3/16" depending on the season. I use figure-8's or slotted holes to mount tops and the like where there could be a problem and I also try to plan to prevent as many problematic situations as I can in the first place.

[Mark Singer]

One very important thing is to understand what each joint is doing. If it is only supporting vertical load....a pinned connection like a bridal joint held with a screw is fine and if over drilled will allow for movement. Isolate each joint and try to understand its function. If it is a glued joint and the grains of the pieces are perpendicular...keep it smaller in width. Solid wood is important in fine woodworking....once a piece moves you will loss the piece...but you will learn what to do and what you are dealing with. Many years ago I made a lacewood table and strongbacked the top with pieces crossing the grain. To make sure it was strong I glued the top to the strongbacks.....in a month or two it was no longer a table....it resembled a feeding trough..major concavity...that was the last time I had any real problems...you learn from mistakes