The Technique of FURNITURE MAKING
PARTICLE BOARDS (CHIPBOARDS)
These are composed of wood chips carefully graded, mixed with synthetic resin glue and either pressed or extruded into rigid, selfsupporting sheets of uniform thickness which are sanded down to close tolerances. Flax- sheaves are sometimes used instead of wood chips (flax boards) and have virtually the same properties, although they tend to be lighter in weight and not so strong for any given density. Considerable research has gone into the development of both types of board, and wood - chip boards are marketed in several forms: flooring grade for general purpose in the building industry, low-density boards for door cores, partitioning, etc., standard all-purpose boards for built-in fitments, panelling, etc., and special furniture-boards (Weyroc 38) for carcass components. The last-mentioned boards are of graded density construction, with the finest chips near to the face, giving a high- density, smooth, close-textured surface eminently suitable for veneering, as there is little tendency for the individual wood chips to show through under high polishes. They are invariably pressed, as distinct from extruded, boards in which the wood chips lie at right angles to the board surfaces, resulting in poor bending strength and lower stability.
Particle boards are heavier than most other wood materials (33 to 40 lb per cu. ft or 528.609 to 640.739kgpercu. m according to the density) as the glue content is relatively high; moreover they have no long fibres and thus have little bending strength and tend to crumble at the edges if roughly treated. Always provided that these boards are not treated merely as substitutes for solid timber and forced to conform to long-established constructional methods, but regarded as valid materials in their own right, well worthy of new methods and applications, there is no doubt whatever that their use will continue to expand, and indeed they will become the standard material for furniture-making. With their obvious advantages this is almost inevitable, for not only do they make use of what is virtually waste material (forest thinnings, bough wood, etc.) but the very fact that they are man-made materials means that there is always scope for research and development in the production of lighter, stronger, Stiffer and cheaper boards.
Working properties
Particle boards are very stable with little dimensional change (shrinking, warping, etc.), and even the absence of long fibres can be turned to advantage, for. as there is no end grain, boards can be glued and butt joined together at any angle without supporting constructional j oints. Working properties are as for other prefabricated woods and present no problems; they can be cut, planed, shaped, routed and bored with all normal tools, provided the cutting edges are kept sharp and feed speeds a little slower than for solid timber. For quantity production, tungsten-carbide cutting edges are recommended, as the high glue content dulls normal steels. Planing to thickness is not advised, as cross planing is inevitable and bound to create rough patches,
but the boards are obtainable in a variety of thicknesses to close tolerances, and where surfaces have to be reduced it is better to sand them down. They are not intended for exterior use as the edges are susceptible to moisture penetration, although some manufacturers now incorporate a proportion of wax emulsion in the glue which gives a certain measure of protection. Screw - and nail-holding properties are not as good as long-grain materials, but sufficient for all but the heaviest loadings.
Uses for particle boards are the same as for blockboards and laminboards, viz. carcasses, flush doors, shelving, panelling, partition - work, etc. A point in their favour is that they have no hidden defects (see Defects in plywoods, etc., below) and are thus eminently suitable for large veneered table-tops polished to a high gloss, and as a substrate for plastic laminates. They can be satisfactorily veneered and the best-quality boards no longer require counter-veneering to hold back any tendency for the wood chips to show through the face veneers. Thicknesses of standard boards range from 3/8 in (9 mm) to l3/8 in (36 mm), and furniture-boards from 1/2 in (12.5 mm) to 7/8 in (21 mm), and boards can be obtained already veneered with a wide range of woods.
