The Technique of FURNITURE MAKING

Edge jointing

133 Jointing details

each alternative board will correct the tilt (133:4). The top board should be swivelled slightly and should bind at both ends, while finger pressure applied simultaneously at both ends will disclose whether there is any tendency to rock, denoting that the edges are twisted. After establishing that the boards seat along their entire length with their faces in one line, then the other boards should be tried in like manner until the assembly is complete.

Gluing up rubbed joints Hide glue should be used, thin and hot, and after slightly warming the boards the first is gripped in the vice and the next tilted against it so that the glue-brush covers both edges at one stroke. The second board is then placed in position and rubbed backwards and forwards three or four times to squeeze out the surplus glue, keeping the hands low down and at either end, if possible, to avoid breaking the joint. Joints over about 3 ft (1.0 m) long should not be attempted single handed, and in any case long lengths should be cramped/ clamped and not rubbed. If the assembly is composed of several boards, they should be glued up in pairs wherever possible, and the glue allowed to harden before any further rubbing; while freshly jointed boards should not be laid flat but stood under their own weight against an inclined batten (133:3), leaving them for at least 24 hours before final surfacing.

Cramped/clamped joints

Long lengths and boards glued with cold-setting resin glues must be cramped and are first planed fractionally hollow. In theory one sash-cramp should suffice, but in practice it is better to use three or more, with one at each end underneath and one in the middle on top to counteract any tendency for the cramps to pull the assembly in warp, checking that the boards seat on the sash - bars, and testing the upper surface with a straight-edge. If resin glues are used, there will be plenty of time to adjust the assembly, tapping down any boards which are inclined to spring. In all gluing operations with resin glues containing acid hardeners, scraps of polythene should be used to isolate glue-covered wood from steel jaws or bars, as otherwise iron staining may result. Surplus glue should be scraped off, for resin glues are hard on cutting edges.

For dowelled edge joints see Chapter 18, Dowelled joints.

Tongued and grooved joints

Where there is considerable loading of the surface, as in unsupported table flaps, etc., edge joints should be strengthened with tongues, which increase the gluing area. Tongues can be worked in the solid (134:1) or both edges grooved and a loose tongue inserted (134:2). These loose tongues were formerly cut from cross grain solid wood but plywood is now univerally used, matching the ply to the thickness of the cutter. The boards are not planed hollow, while the tongue itself, whether loose or worked in the solid, should be a hand - tight fit and no more, and slightly bare of the full depth of the groove to allow for surplus glue, allowing 3/16 in (5 mm) thick tongues entering about1/4 in (6 mm) for 3/4 in (19 mm) boards, and 1/4 in (6 mm) thick for 1 in (25 mm) boards. Thicker boards require double tongues (134:3).

If the grooves are worked with a spindle - shaper or router they can be stopped well clear of the ends and the tongues cut back accordingly (134:5), but if worked with grooving - or combination-plane or circular saw it is more difficult to stop the grooves and they can be allowed to run through, either showing the ends of the tongues—which is not objectionable if well done—or cutting back and filling in with carefully selected end-grain pieces (134:6). Twin grooves and loose tongues (134:2) save timber width; moreover, solid tongues (134:1) worked with matched cutters in a combination - plane are not wholly satisfactory, for the carefully planed edge has to be cut back to form the tongue, and the tightness of the joint may suffer. With machine-cutters, however, solid tongues are so easily formed they are standard practice in production-work and 135 shows the variations possible.

A good tongued and grooved joint will help to pull up a warped board, but should not be relied upon to correct a pronounced problem. Faults in tongued joints are shown in 134:4 where in (A) the tongue is too long, preventing the edges meeting; (B) too thick, forcing the grooves open; and (C) too short, weakening the joint. Typical applications are also shown on this page. Figure 134:7 is a tongued and grooved table-top; 134:8, 9 show two forms of applied lippings to plywood or laminboard, etc.; 134:10 is a light framework with ply panel suitable for small doors, provided the panel is also glued into the groove; 134:11 is a carcass cheek tongued into a post or leg in preference to a series of small tenons which have to be cut laboriously by hand; 134:12 is the corner of a tongued carcass, with (A) a stronger variation as

hole and socket. The hole is bored to the diameter of the head, and the socket cut to receive the shank so that the head of the screw cuts its own path, while the bevel of the countersink pulls the edges together (136). For a tight fit the boards are first tried in position, and the top board tapped a little way home, as indicated by the arrow, to make sure everything lines up. It is then removed, the screw given a half turn, the edges glued, driven home and cramped/clamped. This joint is not now used to any extent, but may be useful for edge joints which have to be worked on before the glue is thoroughly set, and for dry jointing and secret fixings for panelling, wall fittings, etc.

Matched, cleated and battened joints

Traditional custom regards the tongued and grooved joint proper as having loose tongues glued in, and the 'matched' joint with tongues worked in the solid; but the introduction of cheap tongued, grooved and beaded or V- jointed matchings for wall linings usurped the latter term, which is now used solely to describe solid-tongue boards which are dry jointed and secret nailed or screwed to supporting battens or frameworks.

Matched boarding (137:1) has little application in furniture, although cottage-style oak furniture sometimes had doors framed together on this principle. Cleated or battened joints are jointed boards stiffened or supported by screwing ledges or battens to the back (137:2). The screw-holes are slotted as shown in the inset so that the screws can slide either way to accommodate movement, and the principle is

137 Jointing details sometimes used for drawing boards of soft­woods, glued on the edges, deeply saw kerfed on the back to take up any movement and prevented from hollowing or warping on the face by the slot-screwed battens. An alternative method is to taper dovetail the battens (137:3) which do not need either screws or glue.