Blackboards laminboards etc

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In these the principle of construction is a series of wood core strips glued together side by side to form a slab, which is sandwiched between outer layers of veneer or thin plywood whose grains are crossed at right angles to the length of the core strips. In blockboard the core strips should not exceed 1 in (25 mm) in width, although they can be of any thickness dependent on the thickness of the completed board, and in theory at least the grain direction of the strips should run counter to each other, although in practice a random selection is adopted. The outer or face veneers can be a single thickness of from 3/32 in (2 mm) to 9/64 in (3.5 mm); or two veneers glued together with grains parallel to make up a 3/32 in (2 mm) thickness; or, where the length of the sheet exceeds the width, a five-ply construction of core strips, 3/32 in (2 mm) veneer either side at right angles to the core, and outer veneers of about 1/16 in (1.5 mm) parallel to the core.

Laminboard adopts the same construction, but the core strips must not exceed 9/32 in (7 mm) wide, and some varieties, notably Finnish birch, utilize core strips made up from plywood trimmings. Laminboard is heavier and Stiffer than blockboard owing to the greater number of glue-lines, and the use of gaboon or spruce for core strips rather than low-density softwoods; the cost, therefore, is greater, and use is limited to high-class work for which it is eminently suited as it does not exhibit the bumpiness or ripple, i.e. core-strip sinkage, sometimes found in cheaper grades of blockboard.

Battenboard is a variation in which the core strips can be up to 3 in (76 mm) wide, unglued and saw kerfed either side to allow for shrinkage, but it has little if any application in furniture. Both blockboard and laminboard can be obtained in sizes up to 60 in (152 cm) by 120 in (305 cm) and occasionally 144 in (366 cm) in Finnish birch, and up to 60 in (152 cm) by 201 in (510 cm) in gaboon, beech, etc.. both measured in the same way as plywood, with the length of the face grain first quoted. Sheet thicknesses range from 1/2 in (12.5 mm) to 1% in (44 mm) and l7/8 in (47 mm) in flush door sizes only.

Blockboards and laminboards are usually obtainable in beech, birch, limba, gaboon and agba glued to MR and BP specifications. They are not normally marketed in 'exterior' quality, although WBP specification can be obtained. Their chief merits lie in the larger sizes available, their increased rigidity (they cannot be bent to any appreciable radii unless deeply saw kerfed) and the ease with which they can be jointed by the usual methods. They are thus eminently suitable for general carcass-work, table-tops, flush doors, etc.

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