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.
METHOD OF PLOTTING STRING PLAN BY MEANS OF STRIKING POINT LINE AND RUNNING LINES.
The sketch is intended merely as a general guide to the method outlined above, and only a few of the running lines are shown. The dark lines show the direction and position of the bars.