Article on wood shrinkage and effect on furniture

Thanks for posting. 

Good post Carey

A good article on a subject all woodworkers need to have the basics down. Just some of the methods to get there are a bit like homework for a math class. The internet has opened up a library for anyone to use, and many wood species are noted online to their individual characteristics in this regard. I often use the Wood Database where many species are noted, and using the filters on the right side of the main page, a lot of info is available.

My other addition to this is the map of the US, which shows current RH. Each state is clickable as well to get you down to local numbers. It's interesting to check often for a while to see if your area changes much. I know where I am, it is hardly ever the same, day to day.

My other other add is Air dried is much different in this regard to Kiln dried. I see my air dried wood jumping from normal woodworking levels in the dead of Winter, and during the warm months I've seen air dried woods that at one time were 6 to 8% jump to 19 or so. That range makes using it a bit of a crapshoot. Kiln dried wood stays much more stable. The cells shrink under the heat, and aren't available to absorb as much moisture.

George, I think that one difference between air and kiln dried is that heating locks the lignin which is what makes it more dimensionally stable.  Lignin is what gives wood its strength and stiffness.   The extra stiffness means that it is more difficult for the cells to expand so there is not as much room to absorb as much moisture from the air.  Chemical changes in the lignin and cellulose during kiln drying also reduces their ability to absorb moisture or at least slows it down, making the MC of KD wood more stable through wide RH swings.  ...Or something like that.  It has been more than 40 years since I took the wood technology class in college. 

Another good resource is the Woodweb Shrinkage calculator.   If you search for EMC calculator, you will find several websites that you may find useful.

The Wood-Database website George cited above also has a basic explanation of MC and shrinkage concepts for anyone who does not want to wander off into the weeds.