A conventional compression crowned 900 mm long 'control' rib

The RHS steel beam was used for mounting test ribs on the bench, to simulate the rigid mounting conditions of an installed sound board. Tapered spacers were positioned between the sound board test strip and the larger mounting blocks on the RHS, to simulate the sound board seating conditions of Overs piano sound boards.

Compression crowned ("CC") ribs, such as the control rib shown above, will have a smaller 'unstrung' crown radius at the feathered ends. CC rib sound board panels typically are grossly overloaded in compression, even before they are subjected to the downbearing force of the strings. It is not unusual for CC boards to exhibit significant signs of collapse within twenty years, and often much earlier (some overstressed sound boards can exhibit signs of collapse even before the instrument is sold from new). Overs Pianos is currently (2004) replacing a CC concert grand sound board (circ. 1962) from a 'leading' manufacturer, with reverse crown between the bridge and the belly rail in the second top string section (colloquially known as the killer octave).

An early-development-stage I-rib is shown under test below.

A test rib for rib no. 11 of the Overs 225 piano, under a 24 Kg downbearing test load


With reference to the images, please note;

First published 10 June 2004
Last updated, 30 July 2004