When my tuner is tuning my piano, he hits the keys very hard almost as if he’s angry with it! Is this normal? I’m a little afraid that something will break.
To tune a piano successfully, several things are happening, all of which have to be attended to if the piano is to sound in tune even when the tuner has finished. The piano string is under great tension and the forces that hold it in place must be strong enough to keep that tension for as long as possible until the next tuning is due in about six months. The speaking length of the string is defined by the bridge at the bottom end and the capo d’astro bar or agraffe at the wrest pin end. So there are now three different portions of string; the speaking length, and two non-speaking lengths; one between the agraffe and the wrest pin and the other between the bridge pins and the hitch pin which anchors the end of the string to the frame. When the tuner makes an adjustment to the wrest pin he is altering the tension of the string but unfortunately not evenly between the three different sections of the string. If the movement on the tuning lever is to tighten the string (raise the pitch) the portion between the agraffe and wrest pin will have a higher tension than the speaking length because the agraffe will be preventing some of the tension from releasing itself into the rest of the string. Similarly, if the wrest pin is turned to lower the pitch of the note, the top non-speaking portion of the string will be of a lower tension than the rest of the string. To produce a stable tuning the tension throughout the whole length of the string must be equalised as much as possible. This is achieved by striking the key very firmly so that the hammer knocks the tension through the pressure points of both the agraffe and the bridge pins, incidentally also knocking the string out of tune again. The process is repeated making smaller and smaller movements on the wrest pin until stability is assured. Another obvious reason for hitting the keys hard is to make certain that the tuning is firm enough to take any amount of heavy playing by the pianist! If anything breaks while the piano is being tuned, such as a hammer shank, just be glad that it happened while the tuner was still there to repair it for you; it would probably have broken anyway, at a far less convenient moment.