The Technique of FURNITURE MAKING

Metals

METAL FURNITURE

Hitherto metal furniture was largely made of mild steel tube, hence the familiar name 'tubular steel furniture'; moreover, designers tended to think in terms of wood forms and then to translate those forms into metal sections. Modern metal furniture is now designed as such, taking into full account the qualities of stability, flexibility and hardness which allow considerable reduction in sectional dimensions over comparable wood forms. As a viable material for certain kinds of furniture, metal commends itself for its consistent quality which is of great importance in large-scale manufacture; it can be worked to precision limits and its hygienic, non-porous, smooth surfaces, toughness and great strength render it eminently suitable for hospital, kitchen, school, office and dismountable furniture.

MATERIALS

A range of solid and hollow metal extrusions is available, ranging from flat strips to complex hexagonal tube. Cast alloy parts are also made. Stainless steel sheet and tube is attractive, but its high cost and the difficulties of cutting and joining it mean that mild steel is the norm. A variety of surface treatments can be used, as a protection against corrosion and to improve its appearance. Chrome plating is inexpensive, but is prone to rust-pitting. Nickel, bronze or aluminium plating are also used. Various kinds of paints, like stove enamel, and cold-cured polyurethanes are less costly. The best results, where corrosion resistance and lasting good looks are required, are probably attained with plastic coatings. These are of various kinds, and may be chosen to suit the cost and application of the project. One of the most expensive but durable plastic coatings is applied to the clean tube in the form of a thin tubing, heat-shrunk into place. This is difficult to apply to all shapes of component, and so a variety of other methods may be employed either on the whole piece or selected components. One of the most used is powder-coating. With this technique the metal parts are pre-heated in an oven and then sprayed or fluid-bed coated with powdered plastic resin. The thickness of this coat can be controlled by varying the pre-heat temperature. The coated article is then passed through another heat cycle which fuses the powder into a smooth gloss finish.

MANIPULATION

Methods of attachment or jointing are by brazing, torch or arc welding, metal connectors or screw assemblies. Chair posts, table legs, etc. are normally fitted with protective caps of hard rubber, plastic or knock-in wooden caps cut slightly oversize and driven in wedge tight. Connection of wood members, cross-rails, etc. can be done by securing a threaded bolt to the metal section and carrying it though a prebored hole in the wood member with a captive nut in a small mortise which can be tightened up to take up the slack if the wood shrinks. Alternatively, there are knock-down fittings available. Flat strips can be bent cold round suitable forms in a bending machine, but tubes must be filled with rammed sand, steel balls, pitch, etc. and the ends securely plugged or the bending will kink the inner curve. Metal extrusion L-, T-, or u - sections, etc. are filled or packed up with thin metal strips before bending, and heavy sections may have to be heated. For methods of fabrication reference should be made to the standard books on metal-working. However, the following is a brief outline of the properties of metal and the processes involved in working it, many of which would need to be undertaken by specialist engineering or metal finishing firms.