The Technique of FURNITURE MAKING

Bevelled and coopered joints

Bevelled joints are edge joints at any preset angle other than 45°, at which angle they are termed mitre joints, while coopered joints are usually taken to mean several bevelled joints assembled together, as in coopered barrels. Both terms are, therefore, in essence synonymous. Their application is in splay corners and in cylindrical falls, bow fronts, pillars, columns, etc. built up from solid sections and rounded to shape. They can be tongued together, but are more often merely glued, butted together, rubbed or cramped/ clamped and later reinforced with glue blocks, although good joints should not necessarily need them. The usual difficulty is to plane the edges at the required angle. It can be done easily enough on the overhand-planer or jointer with the fence set to the required angle, but hand-planing in a vice and using an adjustable bevel instead of a try-square for testing presents some problems, for it is very easy to lose width if both edges have to be bevelled, thus forming a taper section. A good method is to use support pieces cut at the correct angle temporarily nailed to the planing-board. If the angle of the splay or bevel required is 671/2°, as in building up an octagonal column, then the support pieces must be 221/20 to make up the required 90° at which the plane works (318:3). (Six sides will require angles of 60° and 30°, ten sides 72°

and 18° and twelve sides 75° and 15°). In order to obtain the correct angle of any splay it is first necessary to draw an end view full size (318:1) and set the adjustable bevel, template or protractor accordingly. Having ascertained the correct angle it should then be drawn at each end of the board to be bevelled, and the pencil should also be rubbed along the leading or base edge (318:2). Each section must be to exact width and truly parallel, and the last fine shaving taken off should just—but only just— take out the pencil-rubbing on the base edge, leaving only a darkened arris or corner.

Rubbed joints glued with hide glue present little difficulty, and in building up an octagonal column the eight pieces are first glued in pairs and carefully stood on end or otherwise supported, so that there is no strain on the joints while the glue sets. The quarter sections are then connected into half sections, and finally the two halves are glued together, first trying them in the dry state, for fractional errors do creep in and some adjustment may be necessary. If the bevels are to be glued with resin glue, supporting cradles may have to be used for cramping/clamping up, or the pieces temporarily held with adhesive tape, bound with thick string and wedges driven under the twine to pull the assembly up. A fairly slow - setting glue should be used, for with all the pieces assembled together at the same time the final adjustment must not be hurried, and the cross-distances between the internal flats should be carefully checked. If the column is to be rounded a cardboard circle to the exact finished shape should be used for marking out the ends.

An alternative method of cramping/clamping up splay corners sometimes advocated is to glue temporary wood lugs or blocks to the outer faces at such an angle that the cramp gives a direct pull without slip, but it is a laborious and somewhat uncertain process, and should only be adopted as a last resort. Much can be done with thick blind cord or twine, looped round and twisted with a stick (see Mitre, scribed and scarf joints, Chapter 20) for the pull exerted is fairly considerable. Pads of thick rubber or felt will sometimes prevent a metal cramp slipping on an awkward slope, and it is always worth trying an assembly in the dry state to see whether the cramps will bite.