Thin strips or laminations of wood glued and bent to a curve will not revert to their former shape because each strip is in effect concentric and of fractionally smaller radius than its immediate neighbour which the adhesive will lock firmly in position. Here again practical application is straightforward and equally applicable to fairly large surfaces, door and drawer fronts, etc., or to square sections as in chair-work. The thickness of the individual laminae must depend on the limiting radius of curvature of the particular timber employed, but as a general rule thickness should not exceed 1/8in (3 mm). Thinner laminae of veneer thickness 1/32 in (0.7 mm) and up will yield stiffer, heavier laminations but will take much longer to build up and require more glue. Gap-filling adhesives should be used, preferably synthetic resin, although animal glues (hide, casein) are dependable but more troublesome. The laminae are not crossed as in plywood manufacture for maximum strength is required in the long-grain direction, but are laid the same way and in the same strict order as cut from the log (321:1) with the grains exactly matched as far as possible. If the grain directions in the individual sheets are allowed to cross as in 321:2, the glue will inhibit any actual shrinkage movement as indicated by the direction of the arrows, but the latent opposing forces will endeavour to exercise a turning movement, subjecting the assembly to torsion, and twisting or warping may result. In theory, and provided the grains are straight and matched throughout, it hardly matters whether the number of plies is odd or even, but in practice an odd number of laminae, 9, 11, 13, etc., dependent on the required thickness is generally used, and some slight shrinkage across the width must be allowed for as with solid wood.
Curly grain veneer should be avoided, for the completed assembly will tend to curve with the curvature of the grain, and spiral grain to twist badly. For this reason a predominantly ductile wood like elm is rarely used because of the wildness of its grain, while beech with its straight and even fibres is a firm favourite. As
321 Laminated bends i *
with plywood and laminboard, etc., sheets and square sections will be stronger and stiffer than solid boards in the same thickness.
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