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Preventing warp in pedestal table tops5/17
I am making 30 walnut table tops to go on pedestal stands in a restaurant. The finished tops will be an inch thick and 3ft x 3ft. Glued up of boards between 4" and 7" in width. The pedestal attaches to a spacer in turn screwed to the top. Grain will be alternated as much as possible to help with warping but I am still concerned about warping and cupping of the tops, as there is now skirt to fasten to. For aesthetic reasons breadboard is not an option. Thinking of putting two cleats on either side of the spacer under the table to help with this. Have also been suggested to inlay and screw a couple 1/4 solid steel bars under each top with wiggle room for the screws to allow the wood to move. Thoughts on preventing warping/cupping for a square pedestal table top?
Thanks for the advice!
You can use due diligence to stop cup or twist... At this point it's up too the client.
I make many tops like this. The only way to keep a top from cupping is to make them thicker or make them out of manufactured core.
I'm no fan of adding steel to furniture hoping to control it. 1/4" steel will very easily bend in 3', you would need an angle iron or channel. Consider a taller wood cleat, that tapers near the edge. ABSOLUTELY no glue on the cleat and plenty of slot width for wood movement.
Q: Why does wood move (cup)?
A; Wood moves in response to changes in moisture content typically brought on by changes in relative humidity in the environment.
The above information will replace the steel bars, the apron/skirt and the slaughter of a red hen in the full moon. Might even replace alternating the rings.
David has "hit the nail on the head."
One additional step is to coat all six surfaces (top, bottom, and four edges) of the table with a water-vapor impervious finish. Wax is close to perfect. Acrylic is also close, if thick enough. Other coating may not stand up well to repeated wiping with water and cleaners. End cracks can also develop with wetting.
Note that warp can often be the result of uneven moisture within the piece. A vapor resistant coating helps assure that any moisture change is fairly uniform within the piece.
The flipping of adjacent pieces does not help. Using the correct initial moisture (which means little movement due to moisture change as the piece adapts to its environment in the restaurant), and the various other items mentioned here and by David, are the keys.