Knot (wood)

“ Although one part of the wood, in consequence of the obstruction of the knot, be more dense and resinous, another part, immediately above or below the knot, where the growths are extended to fill up the vacant space, where the worming commences, is less dense, and of inferior durability, and corruption begun, extends. ”

“ The weakening effect is much more serious where timber is subjected to bending and tension than where under compression. The extent to which knots affect the strength of a beam depends upon their position, size, number, direction of fibre, and condition. A knot on the upper side is compressed, while one on the lower side is subjected to tension. The knot, especially (as is often the case) if there is a season check in it, offers little resistance to this tensile stress. ”

“ Limbs have their origin in the pith of the stems that bear them. Any stem is normally one year older than the branch it bears. So the base of any branch is a cone quite buried in the parent stem. A cross-section of this cone in a board sawed from the trunk is a knot. Its size and number of rings indicate its age. If the knot is diseased and loose, it will fall out, leaving a knot hole. The fibres of the wood of a branch are extensions of those just below it on the main stem. ”

“ A layer is placed along the bottom opposite to the eaves, and secured by a strip of wood nailed from rafter to rafter; the layer next above hides this strip, and so the work is carried on to the apex, where a knot cut from an apple-tree trunk, a bunch of fir-cones fastened together, or some such matter, finishes the whole. In districts where ling is not to be had, gorse or furze in short pieces may serve instead, but stout gloves are required to handle it; or the ends of fir branches may do, if nothing better offers.
It is not always easy to decide on the best way of forming a floor. ”

“ The wood is soft, coarse and doesn’t endure well. I have heard it said that a hemlock knot is the hardest vegetable growth of the American woods.”
“Such is the fact; a hemlock knot will turn the edge of a finely tempered axe or hatchet. Now, boys, take a look at the topmost twig, and tell me whether you notice anything peculiar.”
Several replied that the twig drooped several inches to one side, though there seemed nothing remarkable in that fact. Mike gravely remarked:
“The same being a branch, it is trying to bough.” ”

“ Some of our people, who were too lazy to search for knots, split the wood into small sticks, each about the size of a goose quill, and, standing three or four in a vessel filled with sand, gained as much in the way of light as might be had from one pine knot. ”

“ Frauds are sometimes practiced upon those who purchase logs, by driving a knot or piece of a limb of the same tree into the konkus and hewing it off smoothly, so that it has the appearance of a natural knot, but the dissecting process at the saw-mill exposes the imposition. ”

“ To build a fire in the rain with no dry wood in sight seems a difficult problem, but keep cheerful, hum your favorite tune, and look for a pine-knot or birch bark and an old dead stump or log. In the centre of the dead wood you will find dry wood; dig it out and, after starting the fire with either birch bark or pine-knot, use the dry wood as kindling. When it begins to burn, add larger pieces of wood, and soon the fire will grow strong enough to burn wet wood. ”

“ Subsequent growth of wood may completely conceal the stubs which, however, will remain as knots. No matter how smooth and clear a log is on the outside, it is more or less knotty near the middle. Consequently the sapwood of an old tree, and particularly of a forest-grown tree, will be freer from knots than the heartwood. Since in most uses of wood, knots are defects that weaken the timber and interfere with its ease of working and other properties, it follows that sapwood, because of its position in the tree, may have certain advantages over heartwood. ”

“ Wood becomes knotty when it has been ill nourished and has suffered severely whether from winter or some such cause; for in general a knotty habit is supposed to indicate lack of nourishment. When however, after being ill nourished, the tree recovers and becomes vigorous, the result is that the knots are absorbed [2] by the growth which now covers them; for the tree, being now well fed and growing vigorously, recovers, and often the wood is smooth outside, though when split it is seen to have knots. And this is why they examine the core of wood that has been split ”

“ Knots do not materially influence the stiffness of structural timber.
(2) Only defects of the most serious character affect the elastic limit of beams. Stiffness and elastic strength are more dependent upon the quality of the wood fibre than upon defects in the beam.
(3) The effect of knots is to reduce the difference between the fibre stress at elastic limit and the modulus of rupture of beams. The breaking strength is very susceptible to defects.
(4) Sound knots do not weaken wood when subject to compression parallel to the grain.34 ”

“ And in general, wherever one chops or cuts part of the stem or bough, a knot is formed, as though one thing were made thereby into two and a fresh growing point produced, the cause being the mutilation or some other such reason; for the effect of such a blow cannot of course be ascribed to nature.
Again in all trees the branches always seem to have more knots, because the intermediate parts [15] have not yet developed, just as the newly formed branches of the fig are the roughest, [16] and in the vine the highest [17] shoots. ”

“ When it is about fifteen years old the tree blossoms, and then dies. Just as it is about to blossom, it is cut down close to the ground, and stripped of its leaves. The upper part of the trunk is then taken off, so as to expose the pith of the tree, which is broken into a coarse powder by means of a club of heavy wood, having a piece of iron or sharp stone in one end. The whole inside of the tree is broken up till the trunk forms a trough not more than half an inch thick. ”

“ But they don't grow very well."
"They grow pretty long, sometimes," replied Marco.
"At any rate," said Forester, "the branches of trees will not grow from the stems of the trees near the ground, in the woods; and this is of great importance, for, whenever a branch grows out, it makes a knot, extending in to the very centre of the tree. This would injure a pine log very much, as the knot would show in all the boards, and a knot is a great injury to a pine board, though it is of great benefit to a mahogany one." ”

“ The rot in larch taking place in the part appropriate to knees, the forester cannot be too wary in selecting the situations where there is no risk of its attack, for planting those destined for this purpose. It is also desirable, if possible, to have the knee timber in ground free of stones or gravel, as the grubbing in stoney ground is expensive, and the roots often embrace stones which, by the future swelling of the bulb, are completely imbedded and shut up in the wood, particularly in those places between the spurs {95} where the saw section has to divide them for knees. ”

“ It is so secure that it is impossible to remove it by pulling either end of the knot. This differs from the domestic method in which the pile is merely drawn between the warp threads without tying or fastening. In the finer fabrics of the East the knots are so close that it requires careful examination to discover them except in very old rugs where the pile is worn down, then the knot is distinctly seen.
In some parts of Persia the best artisans are men but in most other sections the weavers are mostly women and children. ”

“ The next stage of preparation is that called knotting, the purpose of which is to guard against the knots appearing in the finished work, by stopping their absorbent quality, or closing the apertures of the fibre, and thus preventing the effusion of gum or sap. It is, of course, strongly urged that wood should be thoroughly dry before it is used, but this is not within the power of the painter to control; he must take the wood as he finds it, and must do his best to counteract the effects of the new wood on his work. ”

“ The rows of knots are pressed down, so that their alignment is slightly irregular, and the warp is concealed at back. Warp, almost always wool; in a few modern rugs goats’ hair is used. Each of the threads encircled by a knot is almost equally prominent at back, or occasionally one to each knot is depressed. Weft, wool of medium diameter, frequently coloured red. A thread of weft crosses twice between every two rows of knots. Pile, wool, short to medium, and silky. Border, three to five stripes. Beyond the borders, at each end, is frequently a narrow band of pile. ”

“ One method for best work is to cut out the knot whilst the work is at the bench to a slight depth, and to fill up the hole with a stiff putty made of white lead, japan, and turpentine. There are many ways of killing the knots: the best and surest is to cover them with gold or silver leaf. Sometimes a lump of fresh slaked lime is laid on for about twenty-four hours, then scraped off, a coating of “size knotting” applied, and if not sufficiently killed, they are coated with red and white lead in linseed oil, and rubbed down when dry. ”

“ To make a square knot, take the ends of the rope and pass the left end over and under the right end, then the right over and under the left.
If you once learn the simple formula of "Left over," "Right over," you will never make a mistake and form the despised "Granny," a most useless, bothersome, and deceptive makeshift for any purpose (Fig. 13) . The true "Reef Knot" is merely the square knot with the bight of the left or right end used instead of the end itself. This enables the knot to be "cast off" more readily than the regular square knot (A, Fig. 12) . ”

“ Cottonwood weighs 24.24 pounds per cubic foot, which is approximately the weight of white pine. It has about the stiffness of white oak, but only about eighty per cent of white oak’s strength, and fifty per cent of its fuel value. The wood is very porous, but the pores are small, usually invisible to the naked eye. The medullary rays are small and obscure. The appearance of the wood is not improved by quarter-sawing. The summerwood forms a thin, dark line, so faint that the annual rings are often scarcely distinguishable. The tree is generally a rapid grower ”

“ Cottonwood can be separated from other light and soft woods by the fineness of its rays, which is equaled only by willow, which it rather closely resembles. The wood is largely used for boxes, general construction, lumber, and pulp. ”

“ The knotted timber, of course, is very inferior in strength and value to the clean. We would refer the longer continued flow of sap from maple and birches, which have many side-branches, in part, to the lower or side-branches commencing to vegetate sooner in the {306} spring than the top of the tree; this successive commencement of vegetation prolonging the bleeding.
Again, in larch, we find that by far the hardest and most durable wood is grown upon poor, hard, thin tills (that is, thin of vegetable mould upon the diluvium) , even where the root-rot commences about thirty years of age. ”

“ The first is typical of any dry thin-walled cells, as is usually the case in seasoned white pine and spruce, and in the early wood of hard pines, hemlock, and other species with decided contrast between the two portions of the growth ring. As a rule buckling of a tracheid begins at the bordered pits which form places of least resistance in the walls. In hardwoods such as oak, chestnut, ash, etc., buckling occurs only in the thinnest-walled elements, such as the vessels, and not in the true fibres. ”

“ An innovation in pattern, by copying some strange designs that strike the fancy, is far more likely. These distinctions in weaving may be conveniently divided into those that affect the knot, the warp, and the weft.8
The Knot.—Not only may a knot be tied as a Ghiordes or a Sehna knot, but it may have other distinguishing peculiarities; as, for instance, it may be of fine or coarse wool. This is most conveniently observed at the back, where it will be seen that the knots of rugs such as the Bokhara, Kirman, Joshaghan, and Bergamo are tied with fine yarn ”

“ In ring-porous woods of good growth it is usually the middle portion of the ring in which the thick-walled, strength-giving fibres are most abundant. As the breadth of ring diminishes, this middle portion is reduced so that very slow growth produces comparatively light, porous wood composed of thin-walled vessels and wood parenchyma. In good oak these large vessels of the early wood occupy from 6 to 10 per cent of the volume of the log, while in inferior material they may make up 25 per cent or more. ”

“ The youths observed that most of the eucalyptus trees were tall and slender. The gentleman who accompanied them said that their trunks were often found with a diameter of ten to twelve feet, and some had been measured that were sixteen feet in diameter at a distance of ten feet from the ground. The trees grow very rapidly, and their timber when green is soft, so that they can be felled, split, and sawed very easily, but when dry it becomes very hard. It is a very useful wood, as it is adapted for many purposes. ”

“ In ring-porous species, such as oak, chestnut, ash, black locust, catalpa, mulberry, hickory, and elm, the larger vessels or pores (as cross sections of vessels are called) become localized in one part of the growth ring, thus forming a region of more or less open and porous tissue. The rest of the ring is made up of smaller vessels and a much greater proportion of wood fibres. These fibres are the elements which give strength and toughness to wood, while the vessels are a source of weakness. ”