Another development of Pirelli is the resilient rubber diaphragm with triangular steel loops (493:4) engaged in metal bosses screwed to the
framework of the chair (493:3). They are used instead of webbing for loose cushioning, and the four-point diagonal anchorage eliminates distortion of the side rails, hammocking and localized areas of wear in the cushions (493:5). The diaphragms must be tensioned from 8 to 15 per cent maximum, and a simply-made metal stretching device is obtainable for quick assembly work. They are available in a range of seat sizes from 151/4 in (387 mm) to 221/2 in (571 mm), and therefore the chair must be designed accordingly, though the square format can be stretched to fit square, rectangular or tapered seat frames within the maximum permissible tensioning.
In designing chairs and settees, etc. with resilient webbing or platform suspension in mind, both initial and depressional tension must be considered, with wood sections sufficient for the loading. The position of the webbing strips is also important, whether from side to side or back to front, and here again there must be specific understanding of the tensions involved. Booklets are available from the suppliers giving the relevant details.
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