For the Scientific Americano The use of bent wood for an increasing variety of purposes surpasses the knowledge even of those most familiar with its production. It is used in all departments of business and pursuits of life, wherever man and his products are known. It is as ancient as history, and is found among those in the rudest state of barbarianism. Little is known of the most ancient devices for bending wood, but the oldest patented in England is now nearly a century old, and is used there yet for some purposes. The oldest in the United States was used first in 1794 up to 1821, then patented with but little change. In 1813, at the Woolwich Navy Yard, in England, floor timbers, sixteen inches square, for a man-of-war, were bent over an arc of a circle with a radius of four feet. AH these devices, as well as almost all others subsequently used, restrained, in some degree, that tendency found in wood to elongate its outer curve when under the operation of bending, the same as is now claimed to be done in apparatus brought as near the statt of perfection as the nature of wood and the change of position the particles undergo will admit. The organic structure of all woods of the endogenous or internal growths, and the exogenous or external growths, are similar, and possess the qualities of cohesiveness and compressibility more or less, differing most in the degree or quantity of these two qualities, which make and determine the amount or degree of flexibility and elasticity in any wood. These qualities, with a structure that will admit an y fluid agency to thoroughly penetrate and soften its particles, indicate a wood that may be made to assume any curvilinear shape required for practical use. Then only ordinary judgment and skill would be required to operate good wood-bending apparatus successfully, without any loss occuring from breakage of the wood under the operation of bending, but when the wood has not been seasoned or par- ' tially seasoned, a trifling loss will occur from breakage caused by the shrinkage that all woods are subject to in the process of seasoning. And in the case of unseasoned bent wood, this shrinkage acts upon the fiber of the outer curve, which is always at the point of tension, if not in an actual state of severe tension, for the reason that in deflecting any substance, but particularly wood, either with or without partial restraint, to oppose tension, the wood is acted upon by two forces, the one a crushing force that fore-shortens and upsets the lesser or inner curve, with a tendency to rupture it laterally, the other a tensile force that stretches and elongates the greater or outer curve, with a tendency to fracture it transversely and lift the fiber, which is the most hurtful and oftener occurs to the product. These two forces are divided by a neutral line more or less removed from either curve in proportion to the amount of restraint employed to oppose the elongation of the outer curve, but when nearest the outer curve the best product is had, because all tension, however little, is injurious to the structure of the wood, arising from separating and drawing out the fiber which can never be made to unite again, as in ductile and malleable substances, and because the crushing or compres-ing force improves the wood by forcing the fiber into the interstices or cells, and by interlacing and interlocking the fiber, a product is had nearly resembling the knot or knurl, which is difficult to split or cut, even when rupture is indicated. In order to get the best product of bent wood, the crushing force alone should be used, and it can be if the fiber of the wood be left free to move into the new position in more than one direction from the point of bending, by beginning the curve in the middle of it when the wood is made to assume a long curve first, before taking the shorter curve of the mold, which long curvature starts the fiber throughout the whole wood, and makes more, if not every particle of the wood, accessible to Sthe influence of the softening agent already in it, and consequently more yielding to the action of the crushing force. This force should be produced and governed by fixed and immovable restraint that should not compress the wood while in its straight form ; it should also prevent end expansion and preserve the exact length on the outer curve of the product as that of the wood in its straight condition. Tkis would give a product uniform in density and rigidity throughout its whole length, with the fiber undisturbed on the outer curve, to resist any tendency to change the shape produced. The long curve gradually lessening to the curve of the mold, would amount to double on successive manipulation, and by successive manipulation wood has been compressed into one-third of its primary bulk, with every quality improved to resist decay and wear in usa Nothing can be reasonably urged in support of the popular belief of the necessity to produce or permit tension and elongation in successful wood bending. Tension and elongation are required or permitted only in consequence of the use of imperfect apparatus—elongation is positively indispen-sible in machines that bend from one end, or in one direction from thepoint of bending, and that press the wood against the mold with such power as to prevent all movement of the fiber, producing in advance of the point of bending, a wave-like movement among the fibers of the wood, held rigidly confined and straight, until suddenly made to take the curve of the ' mold. The movement in advance of the bending gradually accumulates a power that resists compression thus attempted, and before the completion of the process, and in order to save the machine or the product, relaxation of restraint is required, and is followed by elongation of the wood, however small it may be. Tension acts upon the fiber, giving a product uneven throughout its whole length, and more liable to change the artificial shape. It is obvious that any augmentation or diminution of restraint during the process, must give just such results, and that the machinery in use for wood bending is far from having reached perfection ; there can and will be machinery constructed to bend large timbers for marine and other structures over any arc or curve that will not require a reduction of its bulk, by the compression of the inner curve, to less than one-half its original bulk. All our past experience has shown wood-bending machinery to be most profitably employed in the production of smaller articles, for which there is an unlimited demand that will continue because of the suitableness and superiority of bent wood for these purposes. J. C. MORRIS. Cincinnati, April, 1858.
This article was originally published with the title "Wood Bending" in Scientific American 13, 34, 270 (May 1858)