File:Canadian forest industries January-June 1922 (1922) (20528684705).jpg

Title: Canadian forest industries January-June 1922
Identifier: canadianforjanjun1922donm (find matches)
Year: 1922 (1920s)
Authors:
Subjects: Lumbering; Forests and forestry; Forest products; Wood-pulp industry; Wood-using industries
Publisher: Don Mills, Ont. : Southam Business Publications
Contributing Library: Fisher - University of Toronto
Digitizing Sponsor: University of Toronto

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CANADA LUMBERMAN 49 The "Grain" of Wood with Reference to Direction of Fibre By ARTHUR KOEHLER Specialist in Wood Identification, Forest Products Laboratory, Madison, Wisconsin. Upon the direction of the grain in woods used in airplane con- struction may depend the strength of the machine and the safety of the pilot. It is, therefore, of great importance that the inspector be familiar with the different kinds of "grain" and be able to determine the direction and slope of the fibers, so that he may eliminate pieces which, on account of their cross-grain, would be likely to reduce seri- ously the margin of safety. There are various kinds of "grain" in wood, and various uses of the word. The annual rings are often considered as constituting the grain. Woods with wide and conspicuous rings are said to be "coarse grained," and those with narrow rings, "fine grained." If each annual ring is composed of a hard and a soft layer, as, for ex- ample, in the yellow pines, Douglas fir, oak, and ash, the wood is said to have an "uneven grain," as contrasted with the "even grain" of white pine, basswood, maple, and mahogany. Occasionally "uneven grain" is used with reference to woods in which the annual rings are very irregular in width. Cypress is often of this nature. When lumber is sawed along the radius of the annual rings, it is said to show "edge grain," that is, the "edge" of the annual ring shows on the face. This is also known as "comb grain" and "vertical grain." When lumber is cut parallel or tangent to the annual rings, it is said to show "flat grain." In grading rules a slope of 45 degrees for the annual rings is considered the line of demarcation between edge grain and vertical grain. The cross-section of timber is usually called the "end grain." For woods in which the annual rings are inconspicuous as in maple, red gum, and mahogany, the word "grain" is rarely used with reference to the annual rings. Thus the expression "coarse-grained maple," "uneven grained red gum," or "edge-grained mahogany" is seldom used. The word "grain" is also used with reference to the size of the pores; woods with comparatively large pores, such as oak, chestnut, ash, and African mahogany, are said to have a "coarse grain," while those with small pores, such as maple, cherry, basswood, and red gum are called "fine-grained." Painters designate them as "open" and "close grained" respectively, the former requiring a filler. Occasion- ally the word "texture" is used in place of "grain" in describing the width or uniformity of the rings or the size of the pores. Since the term "grain" is used in describing a number of differ- ent characteristics of wood, it would help considerably to avoid con- fusion if the width of the rings were expressed by the terms "wide- ringed," "narrow-ringed," or "with rings of medium width;" the uniformity or irregularity in the structure or width of the rings, by "even texture" or "uneven texture"; and the size of the pores, by "coarse texture," or "fine texture." The terms "edge grain" and "flat grain" are more definitely fixed in their meaning and should be retained. A common use of the term "grain" is to describe the direction in which the fibres extend in a tree or piece of lumber. "Straight grain" means that the fibres run practically parallel with the main axis of a tree, or are parallel with the main axis of any given piece. "Spiral grain" means that the fibres extend in an oblique direc- tion circumferentially in the tree, so that if extended they would wind around the tree trunk, forming a spiral, (see Fig. 1). Wood which has a spiral grain, when split radially, produces a twisted surface. "Interlocked grain," also called "cross grain," is caused by alter- nating layers of wood being spirally grained in reverse directions; that is, the fibres put on for a number of years may slope in a right- handed direction, and then for a number of years the slope reverses to a left-handed direction, and later changes back to a right-handed pitch, and so on, (see Figure 2). Such wood is exceedingly difficult to split radially, although tangentially it splits fairly easily. Inter- locked grain is common in black gum, red gum, some Cottonwood, eucalyptus, and many tropical trees. Diagonal grain is the slanting of the wood fibres brought about by causes other than spiral grain in the tree. Usually it is due to sawing straight grained timber in a direction not parallel with the fibres, a procedure to be avoided, if possible, in cutting stock in which strength is an essential feature. Curvature in the tree trunk and other irregularities in the grain outside of local wavy and curly grain may, however, make it impossible to avoid the production of diagonal grain in cutting up certain logs. The common method of cutting lumber is to saw parallel with the central axis, which produces more or less serious diagonal grain in the lumber, depending on the taper of the log, (see Figure 3). Obviously, diagonal grain weakens the lumber, and several mills cutting airplane stock are not cutting parallel to the outer surface of the log. Diagonal grain may also be produced by
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cutting up quarter-sawed lumber and not getting the faces parallel to the annual layers of growth, (see Figure 4), or by cutting up plain sawed lumber and not getting the faces parallel to the direction of the fibres (see Figure 5). Diagonal grain produced in the latter way is difficult to distinguish from natural spiral grain in the tree. How- ever, since so far as is known, they are equally weakening, there usually is no need to distinguish between the two. Both spiral grain and diagonal grain are also called "cross grain." Natural spiral grain can be detected by the twisted surface produced in splitting long pieces, and, according to Oakleaf*, usually by the fact that the parabolas and elipses produced by the intersection of the annual rings with the flat surface, do not extend in the same direc- tion as the fibres. How to Determine the Presence and Slope of Spiral Grain on the Tangential Faces Spiral grain can be detected most easily by splitting wood in a radial direction. This, of course, mutilates the piece and is not always

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