Piano hammers are a critical factor in the tone of your piano. If your piano sounds harsh or too soft, it can often be remedied by giving some attention to the hammers. When a key is struck on a piano, a felt hammer strikes the strings to produce sound. Hammers that are hard, compacted, and worn flat will often produce a very harsh tone. If the hammer still has a rounded strike point with shallow grooves, it can be voiced to improve the tone.
If the hammers are worn so that the strike point has become very flat, as in the photo above, the hammers either need to be reshaped or replaced to achieve the best tone. Reshaping involves the removal of felt from the shoulders (the top and bottom of the hammer as viewed in the photo) in order to restore a proper strike point. Too much material would need to be removed from the hammer in the photo in order to restore the strike point. Doing so would make it difficult to play forte, or at loud levels, because much of the hammer weight would be gone. The hammers in the photo should be replaced with new hammers.
If you are looking to buy a used piano, you should always inspect the hammers to make sure they are still round without deep grooves from the strings. Otherwise you should plan on having the hammers replaced for optimum tone.
If you live in the Boise, ID region and would like to have your pianos hammers voiced or replaced, you can contact me to schedule an appointment.