The Technique of FURNITURE MAKING
Carcass backs
Carcass backs can perform three functions: (1) closing in the opening; (2) adding stiffness and rigidity to the carcass; (3) increasing the back weight, thus reducing any tendency for tall carcasses to topple forward when the doors are opened. The thickness of the back and the method of construction will, therefore, depend on the degree of rigidity and the amount of extra weight required, and there is much to be said for the traditional framed-up panelled back, both from the utilitarian and aesthetic standpoints, particularly if solid cedar is used for its permanent moth-repellent properties. Sheet backs of stiff plywood or laminboard are normal and satisfactory, but thin plywood or hardboard are only used in the cheapest work. An additional advantage of the heavy back is its ability to pull a carcass square if for any reason cramping/clamping pressure has distorted it.
The usual form of panelled back is shown in
194:1, 2, while 194:3 is the flush back of ply or laminboard, etc. Backs for pedestal tables and desks can be in individual units (194:4), or taken across the carcass width in a single sheet (194:6) with a bearer rail dovetailed, dowelled or tenoned between the pedestals to support the lower edge. Figure 194:5 shows the construction of the framed back (194:2) with extra wide top rail cut to fit the shaped top; the stiles and rails are normally from 2 in (50 mm) to 3 in (75 mm) wide and 5/8 in (16 mm) finished thickness, according to the size of carcass. Panels can be 3/16 in (5 mm) or1/4 in (6 mm) ply, or 5/16 in (8 mm) or 3/8 in (9.5 mm) solid wood machined to fit the grooves. Haunching of the tenons is optional, and the framing can be dowelled together instead of the orthodox mortises and tenons. In all cases the carcass base is set back to allow the framing to pass over (194:5A). Backs for glued-on tops are shown in 194:7, with the top bearer rail set in and the stiles rebated/ rabbeted into the cheeks or tongued and grooved, as in 194:9. The long edges of the stiles are beaded as shown. Where the top is mitre or double lap dovetailed or tongued and grooved to the sides, and there is no supporting bearer rail for the top of the framing, the rebate can run through (194:8A), but if the top is not mitred (194:8B) then the rebate must be stopped, or a 1/2 in (12.5 mm) by 3/4 in (19 mm) fixing fillet screwed to the underside of the top to form the rebate. Tongued and grooved backs (194:9) are usually rebated into the top, and fixing screws into the rebate are not objectionable if mounted in brass sockets, but the back can be pocket screwed from the inside if preferred. As mentioned before, the carcass base is set back (194:5A).
Types of solid sheet back are shown in 194:11, 12. Veneered carcasses to stand against a wall are not usually edged on the back, but if edgings are provided they must be carefully laid out. Figure 194:13A is a bad placing of the opposing grooves in which the small section beween the tongues (X) will be lost in the machining unless the edgings are glued on before the side grooves are worked, and even then there will be little strength. Figure 194:13B shows the ideal, but if narrow edges are essential they can be offset as in 194:13c and the edges applied before working the side grooves.
