On Veneering.
In our notice of the interior fittings of houses of the better class, it was stated that the process of veneering is sometimes adopted for wainscoting. This process is most generally used for articles of furniture, and deserves to be noticed on account of its ingenuity.
The employment of wood for articles of domestic use or ornament, gives rise to many departments of mechanical labour, according to the manner in which the grain of the wood is to be made conspicuous or visible. In the antique pieces of furniture still existing in old mansions, the wood employed, such as oak, walnut-wood, mahogany, &c., was always solid; but in modern times, the desire of making a respectable appearance, at as small an outlay as possible, has led to the method of veneering,—that is, making some article of furniture of some cheap wood,—such as deal,—and then covering it with thin leaves or sheets of some more expensive and beautiful wood, such as rose-wood, maple, satin-wood, zebra-wood, pollard oak, &c. So very prevalent has this custom become, that almost every house now contains some article of domestic furniture, whose surface is covered with a kind of wood more valuable than that of which the bulk of the article is made.
It must be obvious, that the mode of procuring or preparing the thin leaves of veneer calls for great care and nicety, since they are seldom thicker than a shilling. When the method of veneering was first introduced, the sawing was effected by hand, in a manner more rude than the necessities of the case warranted; but when circular saws became introduced, they were found very efficacious for cutting veneers. Mr. Brunel, in 1805, took out a patent for improvements in the machinery for sawing timber, in which he employed a large circular saw, composed of several pieces fitted together, and placed in a frame at such an elevation that the lower edge was a little below the lower side of the timber. The timber was placed in a carriage, and moved towards the saw by a rack.
In such a manner as this veneers are now cut from the timber in this country. But it is stated that the Russians have devised a very curious and effective method of cutting veneers, without the use of a saw, and without making any waste of material. It is a planing machine, the action of which is so accurate, that veneers thin enough for the covering of books, and for lithographic and other engravings, have been produced; thus serving the place of paper. The operation is begun by placing the timber from which the leaf is to be cut upon a square axle, where it is revolved, and made circular by a turner’s gouge. The blade of a plane of highly-tempered steel, and rather longer than the cylinder of wood, is fixed at the extremity of a frame six or seven feet in length, in such a manner as to exert a constant pressure upon the cylinder, and pare off a sheet of equable thickness, which folds upon another cylinder like a roll of linen. The frame to which the blade is attached is moveable at its lower extremity, and by the action of a weight it depresses in proportion as the mass diminishes in substance. That this depression may be progressive and perfectly regular, the inventor has appended a regulator to the machine consisting of a flat brass plate, preserved in an inclined direction, upon which the frame descends as the regulator itself is advanced. The motion is communicated to the cylinder of wood by several cog-wheels, which are turned by a crank. One hundred feet in length of veneering may be cut by this machine in the space of three minutes.
When veneers are produced by the action of circular saws, as is now almost universally the case in England, it is evident that both surfaces must be rough, from the marks of the serrated edge of the cutting instrument; and it is in this rough state that they are purchased by cabinet-makers or others who employ them in veneering articles of furniture. The operations which are then to be performed are, to bring the surface of the veneer to a tolerable level, to fix the veneer to the article of furniture, and to clean and polish it when so fixed.
Supposing the top of a sideboard to be the article which is to be veneered. The workman cuts out a piece of veneer, a little larger than is actually required, to allow for waste; and then lays it flat on his work-bench. With a veneering plane—which is a small-sized plane, having an iron jagged with notches like the teeth of a very fine saw—he works steadily over the whole surface of the veneer, carrying the plane in the direction of the grain of the wood. The action of this plane-iron removes all the saw marks, which were irregular in their course, and gives instead of them a series of regular parallel channels from end to end of the piece of veneer; these channels are but small in depth, and their object is to retain the glue which is afterwards used in the process of veneering.
The surface of the deal or other wood on which the veneer is to be laid, is in like manner planed with these parallel indentations; and then the process of veneering proceeds. The wood, having been well warmed before a fire, is coated with warm melted glue; and the piece of veneer is laid down flat on the veneered surface, and rubbed backwards and forwards, in order that the glue which is between the veneer and the under-wood may be pressed into all the little grooves produced by the plane. When the glue begins to get cool, the veneer can no longer be pressed to and fro, and is then left. This glueing has the general effect of making the veneer adhere to the foundation beneath; but there are parts where, from the accumulation of too much glue in one part, or from the presence of air which had not been expelled by the pressure of the hands, the veneer rises up as a kind of blister, convex on the upper surface. The workman employs a veneering hammer to level these protuberances. This veneering hammer is a piece of wood three or four inches long, and an inch in thickness, having a straight strip of iron plate fixed to one edge. The workman, placing the iron edge down upon the veneer, presses on the block of wood with his hand, and works all over the surface of the veneer, expressing all the superfluous glue from the parts which had formed the protuberances. As this redundant glue must have some place from whence to escape, the workman begins rubbing at the centre, and thence proceeds towards the edge, at which the glue finally exudes. There is a curious plan adopted for ascertaining whether there are any parts, imperceptible to the eye, where the veneer does not adhere closely to the foundation—viz., by sound. The workman strikes the veneer all over with a wooden or other hammer; and if the sound be distinct and solid, he knows that the proper degree of adhesion has taken place; but if the sound be hollow and dull, it indicates the existence of a vacant space between the veneer and the foundation; and a greater degree of rubbing or pressing is consequently necessary. If the surface of the piece of veneer be of large dimensions, two workmen are required to level all parts of the veneer before the glue gets cold and loses its fluidity.
But this operation—however good the glue may be, or however well the veneer may be pressed down—is not sufficient to cause the veneer to adhere permanently to the foundation, especially at the edges, where the air is liable to enter, and to cause the veneer to rise. To prevent this inconvenience, the veneer, at and near the edges, is kept down, either by the pressure of heavy weights, or, still better, by the action of screw-presses. These screw-presses consist of two pieces of wood or clamps, which are brought to any degree of closeness by means of two wooden screws, each screw passing through holes in both clamps, the handles of the two screws being, respectively to each other, outside the opposite clamps. The clamps are opened, by means of the screws, to such a width as to admit the edge of the veneered wood between them; and the screws are then worked up till the clamps grasp the wood tightly, where they remain till the glue is quite cold, and the veneer closely adhering to the foundation.
But even all this care is not in every case sufficient to produce a firm adhesion of the veneer to the foundation. It frequently happens that, when the hardened veneered surface is tried with the hammer, a hollow sound indicates that there is yet a place where the veneer has a vacancy beneath it. In such a case, the only remedy is one of a curious kind—viz., to lay a hot iron on the defective part of the veneer, by which the glue beneath is remelted. A small part of the veneer, reaching from the defective part to the edge, is also similarly heated, and the glue beneath remelted. Then, by means of the veneering hammer, the superfluous glue which had caused the defect is squeezed out, and pressed to the edges of the veneer through the kind of channel which had been prepared for it by the heated iron.
Where the surface of the wood to be veneered is more or less cylindrical, such as a pillar, the front of a drawer, &c., the piece of veneer has a curvature given to it, corresponding in some degree to that of the surface on which it is laid, by the action of hot water, before the glueing is effected. By sponging one side of the veneer with hot water, it causes that side to swell, while the other side remains dry; the consequence of which is, that the wetted surface rises into a convex form, leaving the other side hollow or concave:—this is, in fact, an instance of warping, where a thin piece of wood is either unequally heated or damped on opposite sides. The hollow side is then laid on the glued foundation.
When the veneered surface is dry, its edges are trimmed, and its surface scraped and sand-papered, preparatory to the finishing processes which the piece of furniture is to undergo.