This clamp is frequently employed for strengthening and retaining in shape the light covers of boxes, office writing-desks, etc. The board, W, will not be required of large dimensions for the purposes named; and if mahogany be used, it will be unnecessary to "make up" by glueing strips together. If a surface of several feet in extent be required, a frame consisting of four or more parts is constructed, and small thin boards, called panels, are introduced to fill the vacancies between the several members of the frame. The doors and shutters of a house are examples of this description of framing, which is in very general use. All the vertical or longest pieces of the frame are called the styles, and the cross bars which connect them the rails.

The extremities of the rails are usually formed into tenons, which lodge in mortises made in the styles. A groove for the reception of the panel is worked in the styles and rails. The panel should not fit the groove too closely, or it will not have sufficient liberty for expansion and contraction, which, if resisted, will cause the wood to split. The mouldings, when not worked out of the solid, are secured to the styles and rails, and the panels are still unrestrained.

The formation of framed and panelled works can scarcely be considered as easy examples of joinery; we must therefore reserve this subject for future investigation.

It is often necessary to glue a narrow strip on the edge of a board to receive a moulding, etc, in which case it is better to make the addition wider than it will ultimately be required, and when the glue is hard, to cut off the excess of material. By this means we are enabled to make a sounder joint, as the strip is less liable to spring up at the ends, if its width be equal to about three or four times its thickness.

It is sometimes necessary to form a large curve or sweep either by bending the wood, or by cutting it to the required shape. If the sweep be large, bending the material is the most economical process. The simplest but certainly not the strongest method of bending is performed by making several kerfs with the tenon-saw along the edge which is required to yield or stretch. The kerfs must be equi-distant and of uniform depth, and care must be taken when bending not to cripple the work by applying too much force.

When the desired curve is obtained, the ends of the sweep should be confined by securing them to the board on which the work must be laid for glueing. The edge in which the saw kerfs were made being now convex, the kerfs will be found much wider than they were previously to bending the wood. The strength of the work may be considerably increased by filling the cuts with glue and inserting thin wedges, which will also tend to preserve the curvature of the sweep. Sometimes a strip of canvass is glued upon the edge in which the cuts have been made. A nice curve cannot be formed when the outer edge is nicked, as the wood will yield unequally.

If the wood of which the sweep is to be made be not too thick and rigid, it may sometimes be bent by soaking the side which is to be convex with hot water, at the same time exposing the opposite side to the fire. If the work be fixed while hot, it will retain when cold the form thus impressed upon it.

When curved work is required of considerable substance it is usual to build it up by glueing several thicknesses, one upon another, in a caul, or mould, formed of two pieces of hard wood, which have been cut to the proper sweep for our work. The wood of which the curve is to be formed must be even in grain, free from knots, and of uniform thickness.

For some purposes, especially in pattern-making, it is convenient to cut several pieces of the required curve out of comparatively thin "stuff" and to glue them together till the proper thickness is obtained. If the sweep be formed by joining several short pieces end to end, the second layer must be arranged so that the joints shall occur midway between those of the lower course or in the centre of the short pieces. It is easy to perceive that if the joints in the several layers were placed directly in a line, the work could have very little strength; it is therefore necessary to "break joints," as in building a brick wall.

We shall have occasion to speak further respecting the process of "glueing up" works, when considering the construction, various framings, veneering, etc.

Although glue is very largely employed as a means of uniting many portions of the work, yet the carpenter, joiner, and even the cabinetmaker, would be unable, without the assistance of nails and screws, to ensure the requisite strength of those parts which are subjected to severe strains.

In fig. 37 several varieties of nails in general use are shown, but without reference to their size.

1. A form called rose-sharp, largely employed for rough purposes, such as coopering, fencing, and general out-door works, is very suitable for driving into hard wood. Another kind termed fine-rose are used for pine and similar soft woods, and being thinner than the former sort is less liable to split the material. The head of each variety is large and spreading, and very good for holding the work down.

2. This nail, also distinguished as rose, has a flat or chisel point, which is less likely to split the wood than one with a sharp extremity. The chisel edge is placed across the grain, and the danger of spoiling the work by even a slight tendency to split, is avoided, and a nail of this description generally holds more firmly than those with sharp points.

Fig. 37.

3. The clasp nail is largely used by house carpenters in deal and other soft woods. The name is derived from the peculiar formation of the head, which slopes abruptly on opposite sides, clasps the wood when driven into it, and when punched below the surface, the plane can be used over it without being injured.