upright piano hammer replacement
by ranjit, published
This is a quick-and-dirty replacement for a missing hammer on an upright piano. Video at http://www.flickr.com/photos/ranjit/5430307892/
The pictured hammers were lasercut from 1/4" poplar, glued together in pairs to be 1/2" thick and then sanded down to 0.4" to match the original hammers. The extended slot in the bottom allows you to glue the hammer onto the old broken shafts instead of replacing them, and to tilt them to the right to hit the strings at the right angle. The felt is some wool stuff from a craft drawer. Real hammer heads are mostly felt, but I made these ones mostly wood because it was easier.
This design is intended to replace a lost hammer that was broken off very close to the top of the shaft. If the stump of the broken shaft is too short, you'll have to replace or splint the shaft.
Choose your wood stock so that you can approximately match the thickness of the hammers in your piano. It would probably be easier and work as well to use three layers of 1/8" wood rather than two layers of 1/4" followed by several minutes at the disc sander.
After cutting, glue the layers together and sand down if necessary.
Cut strips of felt and glue them to the rounded surface of the hammer. I used wood glue here, and two layers of ordinary craft felt. Although only the very front of the felt actually hits the strings, wrapping the felt around to the back of the hammer head gives it much more surface area to glue, making it less likely to fall off in use.
Dab a fair amount of glue into the slot, let the glue thicken for a minute or so, and fit it onto the broken shaft. (Be careful to wipe up any drips so you don't glue your piano together! I also placed scraps of paper to help keep things from sticking together.) As the glue hardens, you can adjust the tilt and rotation of the hammer so that it hits the strings at the right angle.
I don't know how long these hammers will last before they fall apart or fall off the shafts, but it's better than having a big gap in the middle of the piano!