1 Plywood and laminboards, etc. have no natural line of cleavage and cannot be split across the length or width, as the grain direction of each alternate layer is opposed to the direction of the force. General stiffness and rigidity is also much greater, and a strip of plywood is Stiffer than a strip of steel of equal weight, and therefore thicknesses as opposed to solid wood can be reduced by as much as 25 per cent. Particle boards do not have the same high strength weight ratio and are relatively weak in all directions, nevertheless they have much the same dimensional stability, and sufficient strength and stiffness for most purposes.
2 All prefabricated woods are available in large sheets, sanded smooth to uniform standard thicknesses, thus no preparation is necessary and much intitial labour is saved.
3 Large sheets are always more economical in cutting, and waste factors are much lower, while quality is consistent from sheet to sheet.
4 Construction is balanced, therefore movement is negligible under normal conditions, making them ideal for large or flush surfaces. Plywood in particular possesses a natural resilience which enables it to be bent to reasonably small radii of curvature without damage.
5 The utilization of common woods in plentiful supply, which can be face veneered with decorative hardwoods, conserves stocks of the more valuable timbers which might otherwise be insufficient to meet the demands of modern production.
There are still some lingering prejudices against the use of plywoods but they have no foundation whatsoever, and MDF particle boards are beginning to emerge, not as cheap substitutes, but as logical extensions or adaptations of wood in solid form.
Advantages of solid wood
1 First cost is often less than of plywoods, etc.. in equivalent thicknesses, except for the rarer hardwoods.
2 Solid wood can be jointed with ease, shaped, moulded, carved, and bent to small radii.
3 Badly fitting joints and members out of alignment can be flushed off level after assembly.
4 Edges do not have to be protected or disguised in any way.
5 Solid wood has a natural elasticity without fatigue, thus screws and nails are securely gripped and will not work loose under normal loading. It will withstand rough treatment and can always be resurfaced. It has an effective life of many centuries.
6 It responds to careful finishing and has a depth of surface not obtainable with thinly veneered or composite surfaces.
Generally speaking plywoods, blockboards and laminboards should require no preliminary treatment, as they are invariably scraped or sanded on both surfaces to exact dimensions, but certain wood species, notably gaboon, often exhibit badly plucked grain which should be filled with a glue-absorbent filler (plastic wood, brummer, etc.). Particle boards and hardboards should have the glazed skin broken through with light sanding to enable the glue to take. Cheap foreign plywoods, machine-sanded with flint-papers, should be very carefully examined, sanded afresh and thoroughly dusted, for there have been several cases of embedded flint-dust setting up a chemical reaction with synthetic finishes. Cutting of some plywoods presents difficulties, and certain varieties, notably birch, tend to splinter under the saw. The remedy is either to use finer teeth to the saw, clamp a waste piece firmly under the ply to contain the splintering, or score the cutting-line deeply with a knife in advance of the cut—a preliminary trial will always show what propensity there is to splinter out. In machine-sawing, if the surface breaks out on top. increase the projection of the saw, or. if underneath, then decrease the projection, and if possible keep the board tight to the saw-table with spring arms, etc. Some panel saws now have a built-in scoring blade which finely cuts the undersurface.
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