How pianos are made

The strings of a piano pull on its iron frame with more than 20 tons of force.

stations: 8
things upstream: 51
raw sources: 15
steps from the ground: 8

The short version

A piano is a wooden case holding a cast-iron frame, a spruce soundboard, and steel strings struck by felt hammers. Makers bend the wooden rim, cast the iron plate, string the frame under heavy tension, and build 88 keys with a lever action. Voicing and tuning take as long as the building.

Bend the case

Layers of hardwood are glued and clamped round a form, giving the piano its curved outer rim. The wood is thick because the case has to take the pull of the strings.

Goes in
Lumber Adhesive
Build the soundboard

Thin boards of spruce are glued edge to edge into a large panel and ribbed underneath. Vibration from the strings crosses a bridge to this panel, which moves enough air to be heard.

Goes in
Timber Adhesive
Cast the iron plate

Molten iron is poured into a sand mold to make the plate, a single massive frame. It sits above the soundboard and takes most of the strings' pull.

Goes in
Pig iron
Wind the strings

Steel wire is drawn to size for the high notes. Bass strings are wrapped with copper wire to make them heavy enough to sound low. Most notes use three strings.

Goes in
Steel wire Copper wire
Press the hammer felt

Wool felt is pressed over wooden hammer cores. Felt, first used in pianos by Jean-Henri Pape in 1826, hits the string cleanly and then falls away.

Goes in
Wool fleece
Make keys and action

Eighty-eight keys are cut and mounted on balance pivots. Each key moves a chain of levers that throws a hammer at the string and lets it fall back. A damper stops the string when the key is released.

Goes in
Lumber
String the frame

The plate is set into the case over the soundboard. Strings are threaded over the bridge, round pins in the plate and onto tuning pins, then hauled up to rough pitch.
Voice and tune

A technician tunes every string and works on the hammer felt with needles to even out the tone from note to note. The tuning settles for weeks after.

End of the linePiano

Worth repeating

Pianos can have over 12,000 individual parts.
Modern pianos have 88 keys, with the exception of Bosendorfer and Stuart & Sons models.
Cristofori's piano, invented around 1700, let players change loudness by touch. Its name was originally fortepiano.