Veneers used to be cut by the hand-saw; at present, the circular saw is, I believe, universally employed in England for this purpose, with the advantage, not only of cheapness and expedition, but of a smaller waste of wood in sawdust, and for greater accuracy and precision in the thickness of the veneer — a quality essentially requisite to produce good work in the finished article.
In a large veneer-mill which I had an opportunity, through the kindness of one of our members, of visiting, there are five circular saws. Each consists of a strong, stiff, circular frame-work, of the shape of a plano-convex lens, or rather a low hollow cone, tapering gradually to the edge, from which projects a ring of soft steel a few inches broad, pierced with many holes. The saw is a plate, or rather a flat ring, of well-tempered steel, about twelve inches broad, pierced with as many holes as the former ring, and firmly secured to it by means of screws: a band over the axis of the saw communicates motion to it, by connecting it with the first mover, which is a steam engine.
The wood to be cut is laid on the cross-bars of a frame, which are previously covered with glue, and remains in a horizontal position, loaded with heavy weights, till the glue has become dry. The frame, with the log, or flitch, as it is technically called, adhering to it, is then fixed sideways in a carriage which traverses backwards and forwards, the frame itself being likewise capable of motion at right angles to the run of the carriage, in order to project the log sufficiently to bring it within the action of the saw. The quantity of the latter motion is regulated by a screw, one turn of which throws forward the frame, and, consequently, the log, about 1/50 of an inch.
The saw being put in motion, the workman first turns the regulating screw more or less, according to the required thickness of the veneer; he then, by pulling a lever, throws the apparatus into gear, which gives motion to the carriage, and takes his seat by, the inner, or convex, side of the saw. As soon as the log comes up to the saw, he directs the head of the veneer into a curved frame, which it readily enters, on account of its flexibility, being so very thin, and then employs himself in holding in each hand a chip of wood obliquely against the teeth of the screw, in order to clear them of the particles of sawdust which otherwise would more or less clog them up.
In a minute or two the log has passed the saw, the motion of the carriage is reversed, and it is brought back to the point from which it first started. Being then thrown out of gear, the regulating screw is again turned, to project the log as much as the intended thickness of the next veneer; and then all those motions are repeated which I have already described. The usual thickness of a veneer is about 1/12 of an inch; but some kinds of wood may be cut as thin as about 1/16 of an inch. About half the wood is converted into sawdust.
Of the fine saws employed at these mills, the largest is eighteen feet in diameter, and makes thirty revolutions in a minute. Three are each ten feet in diameter, with a speed of about sixty revolutions in a minute; the small saw is six feet in diameter, with a speed of eighty revolutions in a minute, which is sometimes increased to one hundred, or even one hundred and twenty revolutions. The teeth of the saws are nearly a quarter of an inch deep. A saw lasts about a year; for the first six months it is employed in coarse work, and afterwards, till worn out, in fine work.
The veneer is necessarily split, for an inch or two at its head, in getting it on the curved frame; and as it is likewise liable to split in drying, a thin strip of linen is glued along the two cross edges of each veneer, which prevents this accident: the holes, at least those of an inch or more across, are also covered in the same manner.
The general method of laying down veneers is very simple, although to do this well and correctly requires, as every thing else does, practice, attention, and patience. The under side of the veneer, if previously smooth, must be scored by means of a toothing-plane; but if cut by a circular saw, it generally acquires a sufficient tooth by that operation.
The surface to be veneered is covered over with strong glue, and before it chills or gelatinizes, the veneer, previously prepared and cut to the shape required, is laid down upon it, care being taken, in doing so, to inclose as little air as possible. When it has been pressed down to its proper bearing in every part, the compound piece is enclosed between two hot boards, secured at the edges by thumb-screws, or, which is still better, is put into a press between two hot plates, where it remains till perfectly dry.
The next process is to give a smooth surface to the veneer, which is effected by first filling up any holes by plugs of the same kind of wood cut to fit them, or by making a paste of fine sawdust and glue, and pressing it into the holes by hand, and then by the successive use of small planes, scrapers, files, glass-paper, Dutch rushes, and fish-skin.
Lastly, a varnish is added, which has the effect of bringing up the colour and lustre of the wood, and protecting it from the action of the air. If the colour of the wood is itself unexceptionable, the varnish should be as colourless as possible; but if a little mellowness or warmth is required, a varnish coloured accordingly must be applied.
The so-called French varnish has within the last few years almost entirely superseded the oil varnishes, as being more quickly applied, possessing more lustre and hardness, being much less liable to be injured by any common liquid spilled upon it, and not requiring to be renewed or refreshed except at long intervals. It is made by dissolving lac in spirits of wine, and then shaking it up with olive-oil to the consistence of an emulsion, in which state it must be used. It is fixed on the surface of the wood by means of a linen rubber, applied with a circular or spiral motion.
A. Aikin, Sec., F.L.S. F.G.S., &c.
Read 22d February, 1831.
Transactions of the Society Instituted at London for the Encouragement of Arts, Manufactures, and Commerce – 1836