Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/549

Rh JOINERY.] BUILDING &c., and is commonly called a dovetail. If a portion of the junction is cut off at an angle of 45, as fig. 74, while the portion at b is dovetailed, it is called a mitre dovetail; while if the portion at a (in iig. 75) passes the other portion at right angles, it is called a lap-dovetail. A very good joint is shown in iig. 70, the angles being brought together at an angle of 45, two or more saw curfs are cut with a dovetail saw, and thin pieces of wood glued in as shown ; this is called a keyed mitre. Fig. 77 shows four methods for securing planks together as practised in France during the mediaeval period, from Viollet le Due s JJictiounaire. FlG 7o._Keyed Mitre. He does not appear to show the junction formed by running a tongue of one piece through another piece and pinning it on the outside, as practised now in England in furniture, as tables, Arc. FIG. 77. Mediaeval Joints. Glue is a viscid tenacious matter used as a cement to connect objects together. The common or animal glue is made from certain portions of animals reduced after certain processes by boiling to the required consistency, and dried in cakes. The best marine glue is composed of caoutchouc dissolved in naphtha, to which shellac is added, and heated until amalgamated. It is insoluble in water, sufficiently solid to give strength, and adhesive to an in tense degree. Glue is used principally in putting framed work together, but not at all in fixing; and even for the former purpose it is much less used by good workmen than by bungling hands. When the stuff is well seasoned, and the trying up, setting out, mortising, and tenoning are well and accurately executed, there is no necessity for glue on the tenons and shoulders ; the wedges alone need be glued, to attach them to the sides of the tenons, that their effect may not depend on mere compression. Joiners are gene rally furnished with a cramp, with which to force the joints of framing into close contact ; it is either of wood acting by means of wedges, or of iron with a screw. This, too, is unnecessary with good work, every joint of which may be brought perfectly close without great violence of any kind. The cramp will sometimes give bad work the semblance of good, but it cannot make it really so. If any cracking and starting be heard in the joiner s work of a new building, it generally indicates one of two things : either the cramp has been required in putting the framing together, or, having been put together, it has been forced out of winding in fixing, and the constrained fibres are seeking to regain their natural position. A good workman does not require cramp, nor will his work, if he has been supplied with seasoned stuff, ever require to be strained ; and consequently the cracking and starting of joiners work indicate unfit stuff or bad work, or perhaps both, It is true that glued joints will sometimes fly ; but when they do, there need be no hesitation in determining the presence of both bad work and stuff in an improper state. It is seldom possible to procure boards sufficiently wide Joining for panels without a joint, on account of heart shakes, vit & glu which open in drying. In cutting out panels, for good work, shaken wood should be carefully avoided. That part near the pith is generally the most defective. If the panels be thick enough to admit of a cross or feather tongue in the joint, one should always be inserted, for then, if the joint should fail, the surfaces will be kept even, and it will prevent light passing through. A very good way also is to glue a piece of strong canvas on the back of the panel when the work is not intended to be seen on both sides. Sometimes plane surfaces of consider able width and length are introduced in joiners work, as in dado, window backs, &c.; such surfaces are commonly formed of inch or inch and quarter boards joined with glue, and a cross or feather tongue ploughed into each joint. When the boards are glued together, and have become dry, tapering pieces of wood, called keys, are grooved in across the back with a dovetailed groove. These keys preserve the surface straight, and also allow it to shrink and expand with the changes of the weather. It would be an endless task to describe all the methods that have been employed to glue up bodies of such varied forms as occur in joinery ; for every joiner forms methods of his own, and merely from his being most familiar with his own process, he will per form his work, according to it, in a better manner than by another, which to an unprejudiced mind has manifestly the advantage over it. The end and aim of the joiner, in all these operations, is to avoid the peculiar imperfections and disadvantages of his materials, and to do this with least expense of labour or material. The straightness of the fibres of wood renders it unfit for curved surfaces, at least when the curvature is considerable. Hence, short pieces are glued together as nearly in the form desired as can be, and the apparent surface is covered with a thin veneer ; or the work is glued up in pieces that are thin enough to bend to the required form. Sometimes a thin piece of wood is bent to the required form upon a cylinder or saddle, and blocks are jointed and glued upon the back ; when the whole is completely dry it will preserve the form that had been given to it by the cylinder. The curve should be made a little &quot;quicker&quot; than the curve intended, as the stuff will always spring back a trifle on being released. A piece of work glued up in thicknesses should be very well done ; but it too often happens that the joints are visible, irregular, and in some places open; therefore other methods have been tried. Large pieces of timber should never be used in joinery, because they cannot be procured sufficiently dry to prevent them splitting with the heat of a warm room. Therefore, the external part of columns, pilasters, and works of a like kind, should be formed of thin pieces of dry wood ; and, if support be required, a post, or an iron pillar, may be placed within the exterior column. Thus, to form columns of wood, so that they shall not be liable to split, narrow- pieces of wood are used, not exceed ing 5 inches in width. These are jointed like the staves of a cask, and glued together, with short blocks glued along at each joint. Fig. 78 is a plan of the lower end of a column glued up in staves ; the bevel at A is used for forming the staves, that at B is used for adjusting them when they are glued together. A similar plan must be made for the column, which will give the width of the upper end of the staves. The bevels taken from the plan, as at A and B, IV. 62 FIG. 78. Jointing of Column. upper end of the