Theory and Practice of Piano Construction / With a Detailed, Practical Method for Tuning

by William Braid White

When the scale rib and pressure bar line has been obtained, it is necessary to make provision for the tuning pins, and particular care must be taken that the strings shall not rub against each other owing to incorrect placing of the pins.

When the drawing has thus been completed, we may take up the design of the iron plate. It will be remembered that we calculated a compensation factor for the shrinkage. This factor is ⁵¹⁄₅₀, and all dimensions where shrinkage may have effect must be multiplied by this amount.

Such dimensions are those of the height and width of the plate. Hence the lengths of the bars, the distances between them, and the positions of the bolts and screws as well as the string lengths must all be modified according to the shrinkage factor.

The wooden templet may be taken directly from the wooden table drawing by filling in the outlines and details of the iron plate on the latter and then copying these on to the templet subject to the shrinkage modifications required. It is well to regard one top side and also that at the treble as immovable, and to consider the shrinkage as coming from the bottom to the top and from the bass to the treble.

When the dimensions of the proposed plate are thus laid out on the surface of the templet, the bars, screw-sockets and bolt holes must be copied in wood and laid on the templet in the exact places that they will occupy in the finished plate. Thus we gradually evolve a complete wooden model of the iron plate, so that the iron founders may readily obtain a correct casting.

When the first casting comes back from the foundry, it should be carefully punched for the tuning-pin, bolt and screw holes. The first casting must be considered in reference to the fact that it represents only one shrinkage.

After the second casting is made from the first, the correctness of the calculations may be judged. But not until the first pianoforte is turned out according to the new scale can the designer find out how well his efforts have been rewarded.

Of course, the foregoing directions are but outlines of the method. The true inwardness of scale draughting cannot be explained here, or, indeed, otherwise than by practical experience. A certain facility in mechanical draughtsmanship is essential, and also close attention to the methods that have been laid down in regard to striking points, number of covered strings, number and place of bars, compensation for shrinkage, and the various other points that have been mentioned.

For the convenience of the plate-finisher, wooden patterns are provided, showing the position of hitch-pins, tuning-pin holes, screw-holes and bolt holes, corrected for shrinkage.