Joinery performance: work with wood, not against it
An article by Peter Kaczmar, TRADA Technology, published in TRADA Timber Industry Yearbook 2002
Wood is a truly unique material with some remarkable qualities. It is a sobering thought that at our present level of technology we are still unable to create man made alternatives which can seriously match the astonishing diversity of properties that wood can offer. Indeed one can ask why should we want to when we are able to maintain a replenishable supply of the real thing.
At the macroscopic level different species exhibit widely varying colours, densities and strength properties. Whilst all timbers respond to ambient conditions of temperature and humidity, they do so at different rates and amounts. Even the same piece of wood can show markedly different properties according to the direction in which it is used, including the rate of water uptake or loss and the movement (swelling or shrinkage) resulting from it. At the microscopic level, one is struck by the astonishing complexity, order and functional beauty of this truly remarkable substance we use for building, see Figure 1.
There are two ways of looking at wood as a manufacturing material. One can exploit its property diversity through selection of species and use it to greatest effect through good component design. In such cases, wood is a versatile and sophisticated manufacturing resource. Alternatively, one can consider its unique properties to be a nuisance; a hindrance to the manufacturing process. This is nowhere better shown than in the construction industry where we have grown accustomed to joinery failures resulting from the philosophy of “opposing” the material.
As an example, consider the cabinet-making process where timber is conditioned before it is used. It is selected either as decorative or functional according to its species, colour, figure etc and is machined into an accurately fitting system with built-in design tolerances which allow panels to remain flat and drawers to operate irrespective of the ambient conditions. Now compare the approach all too often adopted by the construction and joinery industries to a not too dissimilar set of problems. Firstly, the joinery may be constructed from inappropriately selected material to a design specification which owes its development more to tradition than changing circumstances of end-use. Next, it arrives on-site where it is stored either outside, unprotected, in the wet or alongside wet trades (usually before being painted) until installation. Such conditions favour distortion. Only when the building process nears completion are the visible parts of the joinery painted.
The catalogue of consequences is predictable; loss of joinery function, paint failures leading to an increased frequency of ill-conceived maintenance (often compounding the original problem) resulting in escalating costs, the eventual development of rot and finally, replacement. The net result is also predictable: Customer dissatisfaction.
