The Technique of FURNITURE MAKING

PRESSING METHODS

Thin sheets or veneers can be pressed in simple male and female formers/forms (321:3), or over

322 Dining chairs by Robert Williams of Pearl Dot. The graceful backs to this design are tapered in thickness as well as being laminated

324 Bending beech chair backs. (By courtesy of Ercol Furniture Ltd)

a male former only in a vacuum-bag press (321:7). Square section laminations can be bent and pressed with metal straps terminating in screw bolts over a male former (321:4), or with segmented female formers G-cramped/ C-clamped in position as 321:5 which will pull the ends in to the curve. Pressure should be applied from the top centre outwards. An inflatable rubber hose can also be used (321:6), but where a straight section meets a curve there is a tendency for the straight to puff out at (X, X) and shaped wood fillers should be used.

One of the best examples of laminated work is the grand piano, which must be made to exacting standards, be immensely strong, rigid and unaffected by the severest climatic conditions. The craft is highly specialized but in essence the case-work is pure cabinet-making. The heart of the piano is the soundboard of quarter sawn Sitka spruce dried to a moisture content of 6 per cent and then planed to thickness, tongued and grooved, glue jointed, sanded to final dimensions and then stored in a kiln at 100°F (38°C) for two weeks. It is then cut to shape, shrunk in an oven at 150°F (66°C) for up to three hours, which slightly bows the board, before gluing on the ribs which are pressed into position with lance-wood 'go-bars'. The bridges of quarter sawn beech are then added, and the completed soundboard is then glued to the supporting belt or inner rim composed of eight 3/16 in (5 mm) Parana pine laminations curved in a shaped 'buck' or jig. The separate shaped outer bend or rim, which is the chief external feature of the piano, consists of six 1/8 in (3 mm) laminations veneered both sides; while sides and top are of mahogany core with 3/32 in (2 mm) obeche strapping veneers and face veneer over; bottom of three deal laminations 5/8 in (16 mm) thick; and panels in veneered particle board for greater dimensional stability. Keyboard cover or 'fall' is composed of solid mahogany strips turned to shape and veneered in a vacuum-dome press, while the
heavy legs and head blocks are built up of seven thick laminations double veneered. The wrest plank which receives the tuning pins is made up of three transverse and two longitudinal laminations of quarter sawn beech or Rock Maple dried to 6 per cent. Resin glues are used throughout, e. g. Aerolite R with CHWhardener and L48 gap-filling hardener, and Aerolite 301 with GBPX hardener. Prior to the advent of synthetic resin glues pianos for export to tropical countries were composed of solid woods elaborately screwed together.