Both are mechanical means of assembly employing a variety of metal or nylon fittings which replace standard jointing procedures. Knock-up fittings are those designed for the speedy erection of structures providing permanent fixtures which will not be dismantled; knock-down fittings speed erection plus the ability to dismantle, i.e. knock down, at any time and for any number of times. In 'theory, at least, manufacturers can produce with these fittings standardized components which can be stored and transported flat for erection later by the retailer or customer in his own home. In practice, many retailers are reluctant to undertake the erection (which is simple enough in all conscience and usually requires only a screwdriver or spanner); they often insist upon delivery in the assembled state and the main advantage is lost, for full knockdown assemblies often cost more to manufacture unless full advantage is taken of systematized production on a large scale. However, many manufacturers do use one or other forms of KU or KD assembly for very cogent reasons: (a) a large proportion of present-day furniture is composed of veneered particle board which does not lend itself to traditional jointing methods; (b) machining processes can be simplified with less handling of components; (c) the spray coating and surfacing of flat components is easier and cheaper than handling bulky items of furniture.
The basic requirements of good KU or KD fittings are that they should (a) positively locate the joint; (b) ensure a tight joint when correctly assembled and tightened; (c) distribute the load evenly throughout the structure. Many different types are available which satisfy these requirements and which can be divided into three categories:
1 threaded fittings in which a suitable receiver or bushing is onset or inset on one component and the other component locked to it with a barbed dowel or metal screw;
2 interlocking fittings in which both components have screwed-on parts which lock together either with screws or by knocking together;
3 cam action fittings onset or inset, in which a hook fixed to one component engages in a cam-operated fitting in the other and is tightened by operating the cam with a screwdriver.
The most usual form in the cheaper ranges of furniture, particularly with the use of particle board, is the threaded fitting, but the fixing is usually visible on the face of the work either as a screw head or a metal or plastic cover plate. Interlocking fittings are usually surface mounted, therefore they are confined to hidden interiors, and while very easy to attach, for there is no machining to be done, they are not so strong or so positive as the cam action fitting which is the method usually adopted for better class work. Representative examples are shown in 278. Figure 278:1 is the barbed dowel and glued-in nylon bush/bushing; 278:3 a shorter version with twin bushes suitable for KU assemblies, and 278:2 a KU and KD form using a shake-proof screw in lieu of dowel which is, however, visible on the face of the work, although detachable brass cover caps are available. Figure 278:4 is the slotted plate for connecting flat panels; 278:5 a corner version; 278:6 a plastic dovetail fitting; 278:7 a bush and screw, easy to fix and with brass cover plate for screw, and 278:8 the mortise type, very neat in appearance and with adequate strength for all normal carcasses. Applications for these fittings are shown in 278:9-17. A typical cam operated fitting is illustrated in 279. This is composed of a plastic cover (279:7A), metal socket (279:7B), connecting screw (279:7c) and eccentric wheel (279:7D). Figure 279:1 shows a corner connection with two wheels; 279:2 a side connection with fluted metal socket and cover screw; 279:3 a slim fitting for carcass thicknesses down to 1/2 in (12.5 mm); 279:4 a double way with two connecting screws and fluted screw
socket; 279:5 the standard version of 279:3 for thicknesses down to 5/8 in (16 mm) especially in particle board, and 279:6 a double way with two wheels and double-ended connecting screw. Applications are shown in a typical large wall unit composed of upper and lower units (279:8), and assembly is effected by insetting and gluing in the metal socket, screwing in the connecting screw to the correct projection to allow the collared head to engage in the eccentric (cam operated) wheel, and turning the wheel clockwise with a screwdriver to engage the cam, after which the plastic cover can be pressed in o
position over the wheel. Figure 279:9 shows a two-way fitting in particle board, and all the fittings are remarkably strong and positive in action, but as with all other mortise types of KD fittings the holes and recesses must be accurately positioned and machined to a constant depth.
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