Wood Expansion/Contraction - Woodworking Talk - Woodworkers Forum
 
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post #1 of 4 Old 11-07-2009, 08:19 PM Thread Starter
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Wood Expansion/Contraction

I noticed over the summer one of the box joints on a small red oak storage cabinet I built last year popped/separated slightly and it appears this may be due to the wood expanding in humid weather. I have a similar issue with cabinet doors in my garage workshop -- they're tight in the summer and fit fine when the weather changes in the fall. Does this have anything to do with how the wood was dried, or is it common in all woods when the weather changes?
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post #2 of 4 Old 11-07-2009, 11:13 PM
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Expansion was discussed earlier. In as few words as possible...

Typically, KD wood is at about 6% to 8% Moisture Content.

If you move the wood to the desert the wood will stabilize at about 3% MC.

If you move the wood to a humid environment (NOT Marine) the wood will stabilize at about 12%.

As a rule of thumb, assume about 5/32" of expansion or shrinkage per 12" of tangential sawn wood.(It may vary by species, HOWEVER the 5/32" is a good rule of thumb. Per the above MC percentage changes.

For radial sawn wood, use about 5/64" as a rule of thumb.

Use the right tool for the job.

Rich (Tilting right)
Huntington Beach, California
Remember that when we have the "BIG ONE" everything east of the Rockies falls into the ocean.

Last edited by rrich; 11-07-2009 at 11:16 PM.
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post #3 of 4 Old 11-08-2009, 06:58 AM
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Quote:
Originally Posted by windstorm View Post
I noticed over the summer one of the box joints on a small red oak storage cabinet I built last year popped/separated slightly and it appears this may be due to the wood expanding in humid weather. I have a similar issue with cabinet doors in my garage workshop -- they're tight in the summer and fit fine when the weather changes in the fall. Does this have anything to do with how the wood was dried, or is it common in all woods when the weather changes?

To add to what Rich said, E&C doesn't have much to do with how the wood was dried. The wood doesn't know what month or what time of the year it is. What does have a bearing is its' exposure to moisture and temperature.

A wood in a stable environment will stay stable as long as the environment remains stable. I know that sounds like a 'so what's new?' The E&C tables are relative to specie, widths and thicknesses, in relation to moisture content. The wider and thicker the wood is the more subjective it will be to changes.

There are givens that affect stability. If I build a piece of furniture and it is placed in a controlled atmosphere, it is unlikely that there will ever be a problem. Most homes in my area are air conditioned most all of the year. Mine for example maintains about A 46% - 50% humidity level. Outside it's a different story. It can be 50% at 10 A.M and at 3 P.M. it could be 100%. It's nothing short of living in the Congo.

One of my most drastic conditions is my front door that faces West. The inside of the door has a daily exposure of about 75 degrees and approximately 48% humidity, but the outside of the door can be 102 degrees at 100% humidity. If the door had a brain it would be insane. Needless to say, it experiences a wide range of movement.






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post #4 of 4 Old 11-08-2009, 08:50 PM Thread Starter
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Thanks, guys. Your insight has been very helpful. I don't have a climate controlled garage/workshop and will keep this in mind the next time I build something I know will expand & contract with the seasons. I think you & I have the same front door, Cabinetman. It sticks in the summer & leaks air in the winter.
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