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Using the Differential Shrinkage and the Cupping of Lumber Spreadsheet

By: Phil Mitchell Wood Products Notes

Wood shrinkage is often calculated with the assumption that the radial and tangential shrinkage occurs parallel to the lumber surfaces. As a result, the calculated shrinkage has a built-in error in calculating the change in dimension as it ignores the curvilinear nature of the growth rings. This paper describes an Excel spreadsheet that considers the curvilinear nature of growth rings to calculate the transverse wood shrinkage and 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.