Q. What causes buckle in veneer? Is it something that my supplier or that I am doing wrong?
A. Buckle is caused by unusual wood characteristics that developed in the tree. These characteristics result in uneven shrinkage which causes dry veneer to buckle. (In the past, poor veneer dryers also contributed, but today’s dryers are much better and do not contribute to buckle.)
So, let’s look at what happens in the tree. Consider a mature tree with branches, reaching 75 feet into the air. The tree weighs many thousands of pounds. This weight, as well as the weight of branches, creates stress within the tree. Also, a crooked tree, probably crooked from wind or trying to fight for sunlight, has more stress than a straight tree. The tree reacts to all these stresses by making abnormal wood known as tension wood (TW).
TW occurs in many hardwoods (leaf trees) and is characterized by higher longitudinal stresses than normally expected or encountered. Although TW fibers can be found throughout the stem, TW fibers that cause buckle concentrate in small regions or bands within the tree.
TW may cause green veneer to buckle as soon as it is cut. At other times, the buckle does not show up until the veneer is dried. TW shrinks more in a longitudinal (up and down the tree) direction than normal wood (that shrinks close to zero) during drying; this difference in shrinkage is the major cause of veneer buckling. Some veneer cutting operators (at least the older operators) may refer to TW as soft spots in the flitch.
Identification of TW
TW is often found in logs that are not straight, but have bow or crook. Another indicator is an eccentric pith; that is, the “bulls-eye” center of the log is several inches or more off-center. TW is also identified by noting fuzzy rather than smooth surfaces. TW fibers or cells are very weak so these weak cells fold over rather than being cut cleanly; it is like cutting a wet noodle. Another visual identification appearance is a silvery appearance of areas of TW, contrasted with the surrounding “normal” wood appearance.
If TW is a costly quality item, I would work more closely with your veneer supplier.
Gene Wengert, “The Wood Doctor” has been training people in efficient use of wood for 35 years. He is extension specialist emeritus at the University of Wisconsin-Madison.
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