Replacing the old and worn out strings on a piano can give it new life and a full, rich, sustained tone. In the piano rebuilding industry, this is referred to as "restringing" a piano. Before the old strings are taken off, it is extremely important for the rebuilder to take several measurements of the existing strings, which are part of the piano's original scale and design. About every six notes or so, on the average, the string (or wire) size will change, although often some sizes will be used for more or fewer notes. The length of the wire and how the sizes run, is just one of the many factors that determine the "scale" of the piano, which is different for every size and make. Measurements are taken of the wire sizes and where they change, where the duplex bars are placed, of the tuning pin sizes and other factors important for the rebuilder to note when planning the restringing.
When strings are pulled up to pitch, they create between 20 to 30 tons of tension on the plate. The experienced rebuilder will let the tension down on the strings gradually and uniformly, so as not to crack the plate. Since various tools are used during the unstringing and restringing process, the rebuilder will pad various parts of the soundboard and inside rim of the piano so that the finish will not be scratched in the process of rebuilding. Some pads were removed for the purpose of these photographs, so that the process can be seen more clearly.
After the plate and pinblock assembly have been refitted into the piano, and all the little plate fittings such as "agraffes" and "duplex bars" reinstalled, the new strings are installed. The bass strings (wound with copper) are made by a specialty string maker, using the old strings or a paper pattern as a template. The treble strings are cut to the proper length by the rebuilder as the restringing is done. There are about 15 different sizes of treble wire used on a fine quality piano. 2 1/2 turns or coils of wire are wound onto the tuning pin, which is then driven into the pinblock in a pressure fit. The hole into which the tuning pin is driven is slightly smaller than the diameter of the tuning pin. This ensures that the tuning pin will resist turning enough so the strings will stay in tune, but not so much that the tuner will have difficulty turning the pin during tuning. This requires a delicate balance and the experienced rebuilder always runs some tests on the pinblock material beforehand to determine the proper diameter of the holes. When a piano is first restrung, the tuning pins will be very tight. With repeated tunings, they will loosen up, making tuning much easier. There are a myriad of factors involved that impact how tight the tuning pins will be when the piano is finally restrung. Handling these factors properly is what separates the master from the apprentice.
After being brought up to pitch, the piano has 3
neat coils of wire on the tuning pins. A piano will undergo several
tunings in the shop to bring it up to its final pitch. The first
year after a piano is restrung, it generally needs more tunings than in
the following years, because strings are still stretching. This is
true of new pianos as well.
To read more about the string replacement process, click on the first photo in this section to see a larger version and then click next to scroll through the rest of the photos. At the bottom of each photo is a description of the process featured in the photograph.