CHAPTER XV.

THE DRAUGHTING OF THE PIANOFORTE SCALE.

Although, for obvious reasons, we speak of it thus late, yet it is true that the first and most important step in the designing of a pianoforte is the draughting of the scale. This process includes a complete planning of the iron plate and of the bridges, in fact of the whole arrangements for stretching the strings and maintaining their tension. This plan must indicate very clearly the exact length both of the vibratory portion and of the waste ends of each string; it must show the place on each string where the stroke of the hammer is to be directed, while the exact positions of each tuning-pin and hitch-pin must be laid down with equal certitude. Further, the place of the belly-bridges, their dimensions and manner of pinning, have to be shown on the drawing. Lastly, the fastening of the iron plate by screws and bolts must be indicated; together with the precise position of each individual screw, bolt and pin.

When this plan is in all respects complete, it has to be transferred to a wooden pattern. The inevitable shrinkage of paper always makes the retention of the proper measurements a matter of difficulty. This may be overcome by making the first drawing upon a sheet of wood, varnished to give a clear surface. If the drawing be made with India ink instead of with pencil, we shall have a complete and permanent record obtained in a superior manner.

When the wooden templet is to be made from such a drawing, it will not be found that there has been the shrinking or swelling caused by the use of paper, and the first drawing, if made after the method described, may be laid aside for any length of time.

Let us suppose that it is desired to draught the scale of an upright pianoforte. Having selected the size of pianoforte that is to be designed and the wooden “table” which is to serve for the drawing surface, we proceed as follows:

First lay down the line whereon all the hammers are to strike the strings. From this line as base we plot out the string lengths and the direction in which each runs; also the distance of each group from the immediately adjacent groups.

Having laid down the striking point line, we next proceed to indicate upon it, by suitable lines, the middle string of each three-string group. For the two-string groups a line is taken in the middle of the two strings. We call these lines “running lines.” Then the string dimensions must be taken into consideration and calculated according to the rules laid down already. The highest treble strings run at right angles to the striking point line, and the running lines indicating the positions of the groups are to be placed accordingly. The distance between the running lines should be a shade more than one-half of an inch at the highest portions of the scale. It is found necessary to draw the running lines with increasing obliquity as their length increases, until at the end of the treble sections they are running at an angle of about 110 degrees counting from the treble end or 70 degrees counting from the bass end of the striking point line.

The lengths of the strings as determined by previous calculations mark the line of the belly-bridge. The bars that are to be cast in the plate must be allowed for in plotting the string plan. It is usual to place one of these at about F₂ and another at C, where the over-stringing customarily begins. The variations of individual scales and the requirements of particular sizes of instruments sometimes cause changes in this regard. This is one of the points that the designer must decide for himself.

The space between the running lines increases gradually as the length of them, on account of their oblique direction and the necessity for providing sufficient space for the dampers and hammers. The actual length of the strings as calculated must be laid down with reference to the striking point line. As has been pointed out, it is found better in practice to have the hammers strike the very high strings a little above the theoretical place. A good average would contemplate one-tenth of the length for the six highest strings, graduating down to one-ninth for the rest of the highest octave and the next below it. Before the lowest string of this last-named octave (C₃) is reached, the striking point is gradually lowered and two or three strings below C₃ it becomes one-eighth.

If we follow out this scheme we obtain the place where the scale rib intervenes at the pressure bar by taking one-tenth, one-ninth or one-eighth, as the case may be, of the length of each string. The remaining fraction of the length represents the correct distance between the striking point line and the nearest pin on the belly-bridge. Thus the belly-bridge and pressure bar lines are automatically formed as we go along.

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.

The belly-man must have patterns for the position of the bridges and for the bridge-pin boring. A wooden pattern is also required for the pressure bar.

When these details are completed, the draughtsman must possess himself in patience until his completed instrument is turned out.

If the rules so carefully demonstrated throughout this treatise are fully digested, the designer will be far on the way towards correct scale draughting. His native cunning, however, must be relied upon to carry him through when written directions fail.