Differential Shrinkage and the Cupping of Lumber
Wood shrinkage is often calculated with the assumption that the radial and tangential shrinkage occurs parallel to the surfaces of either flatsawn or quartersawn lumber. As a result, the calculated shrinkage has a built-in error in calculating the change in dimension since it ignores the curvilinear nature of the growth rings. An Excel spreadsheet model has been developed that considers the curvilinear nature of the growth rings in calculating the transverse wood shrinkage, and estimates the amount of cup that might develop. The model is dependent on wood species, initial and final moisture contents, and location of the board within the log.