Due to the ease of realisation and in most cases the possibility of disconnecting the elements, mechanical connectors are widely used in furniture practice (Fig. 4.29). Staples, like nails, allow easy assembly, which does not require any additional preparation of the elements before joining. The use of staples in the designs of case furniture in comparison with upholstered and skeletal furniture is quite limited and boils down to fastening the rear walls. In upholstered furniture, staples are used to connect most of the elements of frames and to fasten covers to upholstery frames.
Bolts with nuts and screws for metal are used mainly for fixing metal and plastic fittings or accessories. By binding them with wooden elements, hard species of wood should be used, or wood-based materials of a high density. Bending loads and transverse forces produce high pressures of the core of bolts on the peripherals of holes in joined elements, which consequently increases clearance in the node and reduces the strength of the entire structure. By screwing wooden or metal parts to wooden elements of the furniture piece, screws for wood should be used. Before embedding this connector, in order to avoid cracking of the material, it is recommended to make holes with a diameter that is smaller than the diameter of the screw core. In construction practice, it is proposed to use screws with a length of not more than 2/3 of the thickness of the joined elements. By mounting fittings or other elements to chipboards, due to their loose structure in the middle layer, special screws for chipboards are required. These screws are characterised by a greater diameter of the screw core, a larger skip and height of the threat. The holes for the screws are only slightly larger in diameter than the diameter of the screw core. Thanks to this, the screw can independently transform the hole into a nut when
Fig. 4.29 Mechanical connectors: a staple, b nail, c screws for wood, d eccentric joints—box with eccentric joint, core, e screw with blind nut, f screw with nut, g screws for metal, h confirmat screw and i screws for chipboards
being screwed in. Eccentric joints and confirmat-type screws are commonly used in the assembly of case furniture. An advantage of these connections is the possibility of repeated assembly and disassembly of furniture without significant deterioration to their stiffness and strength. A box with an eccentric joint is usually set in horizontal elements, while the core, through the sleeve or without it, is screwed into a vertical element of the furniture body. Binding elements takes place after turning the eccentric joints and causing assembly stress between the wedge and the core head. Drilling for this type of connectors requires special tools or specialised machine tools. If confirmat-type connectors are used (e. g. ф 5 x 50 mm), it is enough to drill a through hole with a diameter of 7 mm in the side wall and a blind hole with a diameter of 5 mm in the horizontal element, in order to embed the connector.