Practical Organ Building

by W. E. Dickson

Fig. 19.

Cut plenty of large openings in the feeder board for the admission of the external air, and in the middle board for the transfer of that air to the reservoir. These openings may be rectangular, say 4 inches by 1½, and there may be fully six of them in each board. After cutting them, convert them into gratings by fitting little wooden bars across them, 1 inch apart, let in flush with the board, and planed level. Each of these gratings will be covered with a valve or clack of stout white leather, two thicknesses glued together, and held down along one edge by a slip of wood and brads. These leathern valves should play with perfect ease, and it is well to thin down the hinge-flap, or cut it half through with a sharp penknife, that the valve may fly open at the slightest pressure of the wind, and may not throttle or retard its passage. It is a common plan to make these valves without a hinge, by attaching pieces of tape to the four corners, and pinning down the ends of the tapes to the board. The whole valve then rises and falls. We prefer the hinge. After cutting your ribs to the proper shapes, in which you can hardly get wrong, sort them into pairs, and glue a long strip of stout white sheep-skin along the edges of each pair. Stout calico or linen may be substituted for leather on the opposite side, namely, the side which will present the inner angle, and in which the ribs will be in close contact when folded together. A glance at Fig. 19 will show that the upper ribs of the reservoir are in a position the reverse of that of the lower ribs. This inversion of the ribs represents the result of a clever invention by one Cummins, a clockmaker. Before its introduction, the air in the reservoir had suffered a slightly unequal compression as the top board descended, in consequence of the closing-in on all sides of the folds of the ribs, which diminished the space occupied by the air. Cummins's ingenious modification at once rectified this inequality, since the upper ribs fold outwards, and allow more room for the air, precisely in the same proportion as the lower ribs fold inwards and diminish the space. An unpractised ear might not, indeed, detect the slight change in the tone of the pipes caused by bellows made in the old-fashioned way, but let us by all means follow Cummins's plan. You will do well first to join the inner lower edges of the upper ribs to the inner sides of the middle frame; then their other edges to the top board at the proper distance from its margin; then attach the upper and outer edges of the lower ribs to the outer edges of the middle frame; lastly, the lower edges of the lower ribs to the trunk-band. All this must be done quickly that the glue may not grow cold; it will much facilitate a distasteful operation to use a small sponge with warm water, passed over the outer or smooth side of the leathern strips as they are glued on. The main hinge of the feeder will be best made by passing pieces of hempen rope through several pairs of holes bored obliquely for the purpose in the feeder board and middle board, and wedged in with pegs and glue. Fig. 20 sufficiently explains this. Two or three layers of the stoutest leather will be glued over the line of junction formed by this hinge. There is no reason why the hinge should not be on one of the long sides of the feeder, instead of its narrow end, if your arrangements for the blowing-handle or pedal render this form of construction desirable. (You have doubtless well considered your blowing mechanism.) The ribs of the feeder being worked in like those of the reservoir, and all the glue dry, fix the bellows in a fully distended position by temporary appliances, and fill up the open corners by gusset-pieces of your best and most flexible leather. Material will be economised and neatness consulted by preparing a paper pattern of the gusset-pieces in advance. Those of the feeder must be very strong, and it may be well, but it is not necessary, to put on a second pair over the first, but not glued to them in the folding or crumpled part. All must be perfectly tight and well glued down in every part. A mere pin-hole will betray itself hereafter by a disagreeable hissing.

Fig. 20.

We had almost forgotten to say that a valve 4 inches square, or thereabout, must be fitted in the middle of the top board to prevent over-blowing. This is generally made of a small board of wood, planed truly level, and covered with two thicknesses of the pallet leather, rubbed with whitening. It opens inwards, and is held closed by any simple application of a stout spring made of much thicker wire than the pallet springs. Fig. 21 suggests one of the very simplest of arrangements. A string, fastened to the under side of this safety-valve, and to the middle board beneath it, may be of such length as to pull the valve open when the bellows are fully inflated; or the valve may be pushed open from above by a wooden arm or catch attached for the purpose to some part of the frame.

Fig. 21.

The apertures for the trunks should be cut in the trunk-band, according to well-digested plans, before the bellows are put together, that there may be no sawdust or chips afterwards to get under the clacks; and it is well to give the whole interior of the bellows two coats of glue-size before the ribs are closed in.