The typical American grand piano is built with a laminated maple rim and spruce beams. The beams are notched or doweled into the rim tying the structure together. The wooden substructure combined with a cast iron metal plate resists tension up to 22 tons on concert grands. This 1973 6' 10 1/2" Steinway Model B grand piano has approximately 20 tons of tension.
Fitting the ribs to the Steinway Model B Grand Piano. Note the tapered ribs and how they follow the graceful curve of the bridge. In the best case scenario, the bridge is centered on the soundboard and ribs.
The new soundboard is stepped with a router to start the tapering. Finished with a hand plane, the soundboard is sanded smooth and is ready for bridge fitting.
Fitting the Bridges to the new soundboard.
Gluing in the new soundboard. It's very important the soundboard has equal amounts of pressure around the rim to insure a good glue joint. Soundboard glue dries as hard as glass and this helps reflect the sound. Typical wood glues are too soft and flexible for instrument building or rebuilding.
Soundboard is finished and new Bolduc pinblock installed.
With the plate in place, a rotary rasp is used to rough in the bearing notches. Then, a brass handled bearing saw is used to accurately set the downbearing (downbearing is the total amount of
pressure of the strings on the soundboard). Some schools of thought recommend a downbearing of 1.5 degrees at the front and back of the bridge.
A beautifully installed soundboard ready for stringing.