Q: Somewhere in my woodworking background, it seems that I learned that wood shrinks or grows about 1/64 inch per 1 degree of moisture across the grain. Is this right?
A: There is quite a bit of variability in shrinkage for the different species. Teak shrinks or swells very little (1 percent size change for an 8 percent MC change) and oak shrinks or swells quite a bit (1 percent size change for less than 3 percent MC change). As a general rule of thumb, kiln-dried lumber shrinks or swells in width about 1 percent for a 4 percent MC change for flatsawn, or about 1 percent for a 7 percent MC change with quartersawn lumber. (Shrinkage or swelling in thickness is about 1 percent for a 7 percent MC change for flatsawn and 1 percent for 4 percent MC for quartersawn.)
Stated another way, a 1-inch-wide piece of kiln-dried flatsawn lumber will shrink or swell 0.0025 inch when the moisture changes by 1 percent MC. A 6-inch-wide piece would shrink or swell 0.015 inch with a 1 percent MC change, which is 1/64 inch. Perhaps this is the basis for your recollection?
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