Wood Movement

[Kim Poindexter]

As a woodworker I am always conscientious about wood movement with my craft. When I lived in the US I never really saw much movement. I lived in Arizona, Oregon, and 1 mile from the Beach in San Diego. When I moved to Fiji I SAW WOOD MOVEMENT. Furniture that had never expanded or contracted such that it was visible now had significant movement. 8" dresser drawers expanded 1/2". So now I really worry about it.

I am looking at building a pedestal table. The entire table will be made with Mahogany as it is cheap here. I will glue up 2" thick boards to a width of approx 40" The pedestals will be of 4" thick stock, glued up to around 30" wide. The pedestals will be heavily carved so it will be 4" thick in the center, but taper down to 2" near the edges. ALL the grain will be running the same direction.

Since the top and pedestals are the type of wood, same grain direction and similar average thicknesses, Can I assume the table top and pedestal with expand and contract nearly identically? Hence I don't need to worry about wood movement for this design?

Thanks,

[Sam Murdoch]

I'll jump in and say that I agree with you - wood movement will be equalized so no tearing apart of the joints.
We could be wrong but I'd risk it.

[Doug Hepler]

Kim,

I think you are right to think about wood shrinkage for a table that size. My recommendation would be to mount the pedestal to the table though routed holes. Here is my thinking:
Quoting Chris Becksvoort (FWW Nov/Dec 2006), "You can predict pretty accurately how much a board will move simply by knowing: (1) the species, (2) the grain orientation (flatsawn or quartersawn), (3) the width, (4) the current moisture content (MC), and (5) the expected highest and lowest MC." The additional information you need is (a) grain orientation (flatsawn or quartersawn), (b) where the table will be going, and (c) whether the mahogany is kiln dried or air dried. Item (a) is because flatsawn wood changes dimension more than quartersawn. Items b and c are indicate how much change in equilibrium moisture content (MC) the table might experience. If the wood is acclimated to tropical conditions and would someday come back to the mainland with you, to go through a winter in a heated dwelling, the change in moisture content could be as high as 10%. Then, the flatsawn surface of the pedestal might theoretically shrink by as much as 3/4" (.0024 x 10 x 30). if the grain orientation of the pedestal and the top are lined up there should be no problem as they shrink together. If the flatsawn and quartersawn orientation of the pedestal and the top are at right angles, they might move as much as 1/4" relative to each other. Your mounting holes should be able to accommodate 3/4" wood movement pretty easily. Or you can buy specialized steel mounting clips that can slide in a groove.

Doug.

[Lee Schierer]

As long as the table stays in Fiji it should be fine. If you move back to Arizona, look out. As long as the relative humidity stays the same the wood isn't going to move. A good design will allow the wood to move if it needs to without compromising the integrity. In the design you are describing, wood movement should not be a problem though your thinner areas are going to change more quickly than the thicker areas.