Most modern factories are laid out on mass-production lines. The earlier factories often had a cabinet shop, which had its rows of benches for individual work; a cabinetmaker needing machining done carried his wood to the machinist. Today the timber is cut to usable sizes in a main conversion shop and brought to the required moisture content in a kilning section. In the kiln, air is forced through stripped stacks by fans that periodically change the direction of the air flow. In recent years radio-frequency heating has been widely used to dry both natural wood and plywood. The applied radio frequency produces molecular activity in wood and resins (such as those in plywood glue); part of the molecular energy is converted into heat that greatly reduces the time required to dry the wood thoroughly and evenly and to set the glue. The wood is placed in a press between two metal plates to which the power is applied; great thicknesses of wood can be dried evenly by this method.
From the drying section the wood proceeds to the planing and jointing shop, in which it is reduced to the required section and any tenoning, dowelling, or dovetailing carried out. There is also a veneer department, and in many respects this has become one of the most important departments. In it veneers are jointed in width where necessary, and a remarkable recent invention is a machine that sews veneers together with fine fibreglass, the stitching passing through half the thickness of the veneer only. It does this with amazing speed and accuracy. Where required, veneers are matched, giving a balanced appearance; and any small defects are repaired by placing a waste veneer beneath, cutting through both simultaneously, and interchanging the cutout pieces. Veneer pressing follows, and, although multiplate presses are still used to an extent, the tendency in large-production work is toward the progressive presser. At one end of this the resin glue is applied with a spreader, the veneers placed in position on the groundwork, and the whole passed in batches beneath the presser where it is heat cured in about a minute and ejected at the other end ready for further operations.
It is in the assembly shop that the line or conveyor-belt system begins. This is not usually in continuous movement but takes the form of a series of loose rollers over which the work can easily be pushed by one man. Special cramping jigs are set up so that, for example, a wardrobe can be glued up in one operation by power-driven rams. The jig ensures squareness, and the resin glue is cured in a matter of seconds by radio-frequency heating. In fact, by the time the operator has applied glue to the joints of one set of parts, the previous assembly has hardened and can be removed to the conveyor, leaving the jig free for another cramping operation.
From this point onward the work remains on the conveyor belt, passing to a sanding shop where joints are levelled and finally to the finishing shop where it is stained, spray polished, and fine sanded and waxed. Lastly there is a fitters’ shop, where doors are hinged, handles put on, mirrors fitted, and so on.
Before passing to stock or to the packers’ department every piece has to be passed by an examiner who chalks any defect or attaches a small, coloured label indicating that there is a fault in either the woodwork or the finish.
Only a constant flow of orders in large quantities justifies such a setup. Smaller firms contract their veneering to outside specialists, have their turning done outside, and also any other work for which they are not equipped. The aim is to maintain a constant flow of production, which involves a balance in personnel in the various departments to avoid a holdup in any stage.