The Technique of FURNITURE MAKING

Laminated insets

Where the required wood member is for the most part straight with a curved portion at the end, the bend can be achieved by saw kerfing the timber and inserting glue-coated laminae of the exact thickness to fill the gaps. The saw cuts should be staggered in the length and spaced within the capacity of the separate tongues to bend to the desired radius. Figure 321:8 makes the process clear.

Laminating compound spapes

Thin malleable veneers will sometimes conform to very shallow curves in two directions, as on the surface of a large sphere, and such double curvature can be assisted by pre-moistening and pressing between heated cauls or formers/ forms, but the amount of stretch must be within the elastic limits of the wood plies otherwise the veneers will crease and crumple like a sheet of stiff paper. In traditional compound work soft burr veneers, notably burr walnut, were first soaked in boiling water and laid with the hammer, using very thin hide glue and going over the work repeatedly until complete adhesion was achieved. Stiffer veneers or more acute curves require actual tailoring of the sheets to fit, and in one method the veneers are either cut into strips or 'fashioned' to fit the curve so that the butt edges of the cutout notches fit exactly. The first sheet is then stapled down to a wooden former, the next sheet glued and applied, removing the tacks in the first sheet and restapling through the top sheet. Each tailored sheet is treated similarly, removing the tacks and restapling, and leaving the tacks in the last sheet until the glue has set. In another method each sheet is fashioned as before, and the tailored cuts soldered together with hide glue and formaldehyde, using a heated iron to set the glue. Cold glues are used for assembly and the top sheet is strapped with adhesive tape. Templates can be used for cutting the veneers, but several will be required as each sheet will differ fractionally and the tailored cuts should be staggered wherever possible.

Heat setting of bends

A range of slow hardeners is available for synthetic resin glues which will allow plenty of time for complex assemblies in handwork. For production-work low-voltage strip heating is used extensively to accelerate the setting time, and this releases the formers/forms for rapid turnovers.

Continuous strip laminations

In quantity production such work is usually undertaken by specialist firms using sophisticated processes and considerable technical know-how. Figure 323 shows a range of production bends.

Bending plywoods, etc.

Fairly stiff resin-bonded plywood to WBP specification can be bent more readily if one side is wetted, or conversely the other side heated. Much depends on the thickness and number of plies, the direction of the bend in relation to the grain direction of the stout hearted core, and to the timber species of which the plywood is composed, therefore actual tests are necessary. If the plywood sheet is too stiff to take the curve two or more sheets of thin plywood to make up the thickness can be glued and bent between simple formers/forms or merely stapled together as practised in boat hull building, for each sheet becomes concentric and the adhesive will lock the fibres and hold the curve. An admirable plywood for this purpose is Vi6 in (1.5 mm) birch three-ply, readily obtainable, which can be rolled up like a sheet of thin cardboard. Heat softening of wood was well known to traditional craftsmen, who bent their boxwood lines for delicate inlay (purffing) by repeatedly passing them over a heated metal pipe or rod.