CONSTRUCTION OF A BOX, ETC.

55

parallel rule,) which might happen if the dove-tails, shown on a larger scale in fig. 20, were loosely fitted.

When the grain of the four sides, A, B, C, D, runs in the same direction, or parallel with the edges of the box or drawer, as shown by the shade lines on A and B, and the pieces are equally wet or dry, they will contract or expand equally, and without any mischief or derangement happening to the work; to ensure this condition, the four sides are usually cut out of the same plank. But if the pieces had the grain in different directions, as C and D, and the two were nailed together, D, would entirely prevent the contraction or expansion of C, and the latter would probably be split or cast by the restraint. When admissible, it is therefore usual to avoid fixing together those pieces, in which the grain runs respectively lengthways and crossways, especially where apprehension exists of the occurrence of swelling or shrinking.

A wide board, fig. 21, composed of the slips A, B, C, D, E, (reversed as in diagram, fig. 17, page 51,) is rendered still more permanent, and very much stronger, when its ends are confined by two clamps, such as G, H, (one only seen;) the shade lines represent the direction of the grain. The group of pieces, A to E, contract in width upon the line A, E, and upon it they are also flexible, whereas the clamp G, H, is strong and incapable of contraction in that direction, and therefore unless the wood is thoroughly dry the two parts should be connected in a manner that will allow for the alteration of the one alone. This is effected by the tongue and groove fitting as represented; the end piece, G, H, is sometimes only fastened by a little glue in the center of its length, but in cabinet-work, where the seasoning of the wood is generally better attended to, it is glued throughout.

56

MODES OF CLAMPING WIDE BOARDS.

If the clamp G, H, were fixed by tenons, (one of which, i, j,

is shown detached in fig. 22,) the contraction of the part of

the board between the tenons might cause it to split, the distance between the mortices in G, H, being unalterable; or the swelling of the board might cause it to bulge, and become rounding; or the entire frame would twist and warp, as the expansion of the center, might be more powerful than the resistance to change in the clamp, and force it to bend.

It is therefore obvious that if any question exist as to the entire dryness of the wood, the use of the clamps is hazardous; although in their absence, the shrinking might tear away the wood from the plain glue joint, even if it extended entirely across, without causing any further mischief, but more generally it would split the solid board.

Another mode of clamping is represented at K; it is there placed edgeways, and attached by an undercut or dove-tailed groove, slightly taper in its length, and is fixed by a little glue at the larger end, which holds the two in firm contact: each of these modes is frequently employed for the large drawing boards required by architects and engineers for the drawings, made with squares and instruments.

From a similar motive, the thin bottom of a drawer is grooved into the two sides and front, and only fixed to the back of the drawer by a few small screws or brads, so that it may swell or shrink without splitting, which might result were it confined all around its margin. It is more usual, however, to glue thin slips along the sides of large drawers, as in fig. 23, which strengthen the sides, and being grooved to receive the bottom, allow it to

PANELS AND FRAMES. GLUE.

57 shrink without interfering either with the front or back of the drawer.

In an ordinary door with two or more panels, all the marginal pieces run lengthways of the grain: the two sides, called the stiles, extend the whole height, and receive the transverse pieces or rails, now morticed through the stiles, and wedged tight, but without risk of splitting, on account of their small width; each panel is fitted into a groove within four edges of the frame. The width of the panel should be a trifle less than the extreme width of the grooves, and even the mouldings, when they are not worked in the solid, are fixed to the frame alone, and not to the panel, that they may not interfere with its alterations; therefore in every direction, we have the frame-work in its strongest and most permanent position as to grain, and the panel is unrestrained from alteration in width if so disposed.

This system of combination is carried to a great extent in the tops of mahogany billiard tables, which consist of numerous panels about 8 inches square, the frames of which are 3 in. wide and 1 in. thick; the panels are ploughed and tongued so as to be level on the upper side, and from their small size the individual contraction of the separate pieces is insignificant, and consequently the general figure of the table is comparatively certain. Of late years, I am told*, that slate, a material uninfluenced by the atmosphere, has been almost exclusively used; the top of a full-sized table, of 12 by 6 feet, consists of four slabs one inch thick, ground on their lower, and planed by machinery on their upper surfaces: the iron tables are almost abandoned for several reasons. Large thin slates are likewise used by engineers and others for drawing upon, and also in carpentry for the panels of superior doors.

SECT. III.-ON GLUEING VARIOUS WORKS IN WOOD.

GLUE is the cement used for joining different pieces of wood; it is a common jelly, made from the scraps that are pared off the hides of animals before they are subjected to the tan-pit for conversion into leather. The inferior kinds of glue are often contaminated with a considerable portion of the lime used for removing the hair from the skins, but the better sorts are transparent,

* By Mr. Thurston, of Catherine-street.

58

PREPARING THE GLUE, ETC.

especially the thin cakes of the Salisbury glue, which are of a clear amber colour.

In preparing the glue for use, it is most usually broken into small pieces, and soaked for about twelve hours in as much water as will cover it; it is then melted in a glue-kettle, which is a double vessel or water bath, the inner one for the glue, the outer for the water, in order that the temperature applied may never exceed that of boiling water. The glue is allowed at first to simmer gently for one or two hours, and if needful it is thinned by the addition of hot water, until it runs from the brush in a fine stream; it should be kept free from dust and dirt by a cover, in which a notch is made for the brush. Sometimes the glue is covered with water, and boiled without being soaked.

Glue is considered to act in a twofold manner, first by simple adhesion, and secondly by excluding the air, so as to bring into action the pressure of the atmosphere. The latter however alone, is an insufficient explanation, as the strength of a well-made glue joint is frequently greater than the known pressure of the atmosphere: indeed it often exceeds the strength of the solid wood, as the fracture does not at all times occur through the joint, and when it does, it almost invariably tears out some of the fibres of the wood: mahogany and deal are considered to hold the glue better than any other woods.

It is a great mistake to depend upon the quantity or thickness of the glue, as that joint holds the best in which the neighbouring pieces of wood are brought the most closely into contact ; they should first be well wetted with the glue, and then pressed together in various ways to exclude as much of it as possible, as will be explained.

The works in turnery do not in general require much recourse to glue, as the parts are more usually connected by screws cut upon the edges of their materials themselves; but in those cases in which it is needful, the mode of proceeding is so completely similar to that practised in joinery works, that no separate instructions appear to be called for, especially as those parts in which it is required, as for example the Tunbridge ware, &c., partake of the nature of joinery work.

When glue is applied to the end grain of the wood, it is rapidly absorbed in the pores; it is therefore usual first to glue the end wood rather plentifully, and to allow it to soak in to fill the grain,

GLUEING BOARDS, SLIPS, AND BOXES.

59

and then to repeat the process until the usual quantity will remain upon the face of the work; but it never holds so well as upon the lengthway of the fibres.

In glueing the edges of two boards together, they are first planed very straight, true, and square; they are then carefully examined as to accuracy, and marked, to show which way they are intended to be placed. The one piece is fixed upright in the chops of the bench, the other is laid obliquely against it, and the glue-brush is then run along the angle formed between their edges, which are then placed in contact, and rubbed hard together lengthways, to force out as much of the glue as possible. When the joint begins to feel stiff under the hand, the two parts are brought into their intended position and left to dry; or as the bench cannot in general be spared so long, the work is cautiously removed from it, and rested in contact with a slip of wood placed against the wall, at a small inclination from the perpendicular. Two men are required in glueing the joints of long boards.

In glueing a thin slip of wood on the edge of a board, as for a moulding, it is rubbed down very close and firm, and if it show any disposition to spring up at the ends, it is retained by placing thereon heavy weights, which should remain until the work is cold but it is a better plan to glue on a wide piece, and then to saw off the part exceeding that which is required.

Many works require screw-clamps and other contrivances, to retain the respective parts in contact whilst the glue is drying; in others the fittings by which the pieces are attached together, supply the needful pressure. For instance, in glueing the dovetails of a box, or drawer, &c., such as fig. 19, page 55, the dovetails, if properly fitted, hold the sides together in the requisite manner, and the following is the order of proceeding.

The dove-tail pins, on the end B, fig. 19, are first sparingly glued, that piece is then fixed in the chops of the bench glue upwards, and the side A, held horizontally, is driven down upon B by blows of a hammer, which are given upon a waste piece of wood, smooth upon its lower face, and placed over the dovetail pins, which should a little exceed the thickness of the wood, so that when their superfluous length is finally planed off, they may make a good clean joint. When the pins of the dove-tails come flush with the face, the driving block is placed beside them