Why do piano hammers need to be replaced?
Playing the piano compacts and wears down the wool fibers that make up the piano hammer felt. The piano sound, mainly tone and power, are greatly affected by this wear. Piano hammers are often reshaped and voiced to restore the ideal piano sound. However, after repeating this procedure a few times, the hammer will not have enough felt to reshape and will have to be replaced.
To start, measurements are taken from the old hammers and new hammers are ordered. The piano action is usually taken from the piano and transported to a workshop. The old hammers are taken off and the new hammer adventure begins.
Bore (drilling) the piano hammer
Measurements from old hammers are used to find the correct drilling angles. These recreate the exact point the hammer will make contact with the strings. The jig in the picture is used to precisely drill at the correct placement and angle of the hammer.
Cove & Taper the hammer tail
To cove and taper the hammer reduces the hammer's overall mass and gives the installer a chance to find a balance between the weight of the hammer and the keys. Originally, the keys were prepared to off-set the weight of the hammer. Now, we aim to recreate or improve touch by manipulating the weight of the hammer. The picture to the left shows a tapering jig.
The arch is important for adequate checking. Checking happens when the hammer is falling back down from striking the string. The arch gets caught by a back-check and instantly ready to be played again. If not for its shape, the tail of the hammer would make contact with the back-check on the way up and fail to hit the strings. The arch is created using a coarse grit sandpaper. It is one of the only places in the piano that friction is welcome.
After all this wood work is done, the hammers are ready to be positioned on the shanks. The strike point (the point where the hammer contacts the string) is placed tonally in the piano using sample hammers or found using the existing hammers. They are glued into place, the shanks are trimmed, and then the action is ready to be put back into the piano for the final process.
When the new hammers are back in the piano, the action should be regulated. Any new action part will often require adjustments made after installation. Regulation helps keep your piano in good working condition and reduces the amount of wear on all action parts.
Tuning and voicing are the last and final steps to installing new hammers. The hardening and softening of the hammer felt will brighten or darken the sound that is produced when the hammer hits the string. With a few voicing techniques, the technician can manipulate the sound to fit the needs of the musician.
This article provides a general insight on why pianos need new hammers and a small glimpse of what is involved. This procedure should only be preformed by a professional piano technician.
JOSEPH RAVILLE, RPT
Dallas Piano Tuner
Up to Pitch LLC