The Value of Fast- Versus Slow-grown Black Walnut Trees
Important considerations in grading black walnut veneer include length, color, structure, figure, and yield. It seems paradoxical to some people that the wood from fast-growing patented trees and their descendents, Successor GST, could be as valuable as other veneer-grade black walnut trees. When they examine the wood cut from these trees, they usually change their minds. But despite visual proof to the contrary, some continue to insist that if a tree grows too fast, there must be something wrong with it.
That's one reason George Englerth, a research technologist at USDA's Forest Products Laboratory (1) in Madison, Wisconsin, decided to test these assumptions about the differences between fast- and slow-growing black walnut. What follows are excerpts from his report.
Toughness and machining tests were conducted on wood from slow-, moderate-, and fast-growing trees. Planing is the most common and most important operation in the utilization of hardwoods as lumber, because a smooth surface is essential for subsequent sanding and finishing. Defects in planing consist of chipped grain, raised grain, fuzzy grain or chip marks. Fuzzy grain and chipped grain are the two defects usually related to the wood characteristics.
Toughness
Toughness is a measure of the wood's ability to resist shock and is an important property in uses such as chairs, tables, sporting goods, musical instruments, and so forth. Toughness is a function of the wood's specific gravity, its ability to withstand compression failure, the presence of tension wood or decay, knots and grain deviation. The higher the specific gravity, the tougher the wood and the greater its ability to resist shock. The specific gravity of the fast-grown wood was found to be 21 percent higher than the slow-grown wood and 10 percent higher than the moderate-growth wood.Planing
In these tests, the depth of cut was 1/8 inch with ten knife cuts per inch. The boards were planed at a moisture content of 12 percent and evaluated on both sides. No defects of any type occurred in the wood from the fast-grown tree. Two small knots were present in two of the eight boards from the moderate-growth tree, and very slight chipped grain occured in the distorted grain around these knots. Five of the eight boards from the slow-grown trees had defects from planing. Four had fuzzy grain which was in connection with the presence of tension wood in the upper bolts. Four had chipped grain in connection with dostorted grain around knots or swirls in three instances, and from sloping grain in the other. Mr. English concluded that the rate of growth and specific gravity had no influence on the occurance of planing defects. However, distorted grain around knots and swirls is directly related to the growth rate. That is, knots heal over more slowly in a slow-grown tree and the development of straight-grain wood is slower. Also, slow-grown trees usually have more taper, and sloping grain may be a factor in the occurance of planing defects.Shaping
Samples of each type of tree were hand sawed to a curved outline of the final shape, fastened to a jig, and fed past two spindles rotating in opposite directions at 7,200 RPM. Other than slight roughness on the end surfaces of the samples from the slow-grown tree, all samples were free from defects of any type.Turning
Once again, growth rate and specific gravity had no effect on the quality of the turnings. The presence of tension wood in the slow-grown specimens causes some fuzziness of the spindle portion of the samples.Appearance
The wood from the fast-grown tree generally had more variation in grain pattern [and therefore a more desirable appearance] than that from the slow-grown tree.Notes
- Excerpted from Machining and Other Properties of Fast- Versus Slow-grown Trees by George H. Englerth, Research Technologist, Forest Products Laboratory, Forest Service, U.S. Department of Agriculture, Madison, Wisconsin.
- (1) Maintained in cooperation with the University of Wisconsin.
- Italics added for emphasis.