Practical Organ Building

by W. E. Dickson

Fig. 22.

The little contrivance a b c d, Fig. 22, is to ensure the simultaneous rising of the top board and middle frame when the bellows are in action. It may be conveniently made of hoop-iron, but oak or any hard and strong wood will be equally good. If some such contrivance were not introduced, the top board and upper ribs would rise first on the working of the feeder, and the frame and lower ribs would follow in their turn. This would cause inequality of pressure, since the top board would not at once bear up the weight of the frame and lower ribs. The little jointed apparatus redresses this by causing the whole of the ribs to obey the first admission of air. A simpler form of it will be found in Fig. 22a.

We are building a very small organ, but, desiring as we do to give as much completeness to this treatise as circumstances will allow, we here explain that in larger instruments two feeders are generally or always introduced, unless, indeed, a "cuckoo feeder" is used, which practically amounts to the same thing, being a long board hinged to the under side of the middle board by a stout transverse piece in its middle, and provided with two sets of ribs, each set filling up the space from the middle hinge to the end of the board. This feeder supplies wind with the upward as well as the downward stroke of the bellows-handle, but it would not be suitable for an organ in which the blowing is effected by the foot.

Fig. 22a.

We may have readers who are so fortunately circumstanced as to be able to apply water-power to their bellows. In this case two feeders should be fitted in order to utilise both strokes of the ingenious little machine, which consists essentially of a piston moving water-tight in a cylinder provided with a valve which admits water alternately above and below it. This is not the place for entering on a discussion of the conditions essential to the due working of the water-pressure engine; they may be studied in any modern treatise on hydro-dynamics; it is enough for our present purpose to say that a cylinder not larger than a common wine-bottle will give ample power for such an organ as ours, provided that the pressure on the piston be not less than 30 lbs. to the square inch, and that the supply-pipes be of ample size. Water, it must be remembered, does not expand like steam when admitted into an empty space, or rather into a space occupied only by atmospheric air; hence large pipes, large valves, and large ports, or valve-openings, must be provided, that the water-pressure, irresistible when properly applied, may be thrown at once upon the point where it is wanted. But this is by the way, and we will only add that the water machine should be in a room or cellar below or adjoining that in which the organ is placed, as a slight noise is inseparable from its action, and it should act on the feeders by a wooden or iron rod brought up through the floor. Still better if the whole apparatus, feeders, reservoir, and all, can be down-stairs or in a neighbouring apartment, the trunks only passing through the wall or floor. In very large modern instruments the feeders, worked by steam or water, are commonly made to move horizontally, in a way which will be understood if we imagine an accordion or concertina laid upon its side. When the reservoir is fully inflated it acts upon a valve, which reduces or cuts off the supply of water or steam.

The trunks are rectangular wooden tubes made of half-inch pine, and well jointed. In their course from the trunk-band to the wind-chest right-angled mitres are permissible, for it is a mistake, though a common one, to imagine that the wind rushes in an impetuous stream along the trunks as it does (for instance) along a conveyancing tube when its pallet is open. The trunks are simply connecting links between the reservoir and wind-chest, but they must be large enough to ensure an equality of wind-density in both wind-chest and reservoir under all demands on the part of the player. Our trunk may be 5 inches by 2, inside measurement; or it may be 9 or 10 inches wide by only 1; or we may make it 3 or 4 inches square, as may suit our plans. The ends of the trunk should not be glued into the openings cut in the trunk-band and wind-chest. The ends, reduced by half the thickness of the wood, and brought to a shoulder, should be glued into an opening in a small board, an inch or two larger on all sides than the area of the trunk. Engineers would call this a "flange." This flange being leathered, and the aperture of the trunk cut out, it may be pressed with four or more screws against the margins of the openings with which it is in communication, and will thus be removable at any time if the organ is taken down or altered. The interior of wind-trunks should be well coated with thin glue, and the exterior should be painted. Some builders prefer to cover the exterior of their trunks with paper, and to line the ribs of the bellows with the same material, applied with common paste. Trunks have been made, too, of zinc, and oval in section.

The frame of the organ, whatever its form or plan, should be very strong and solid, and should stand firmly in its place on the floor without any tendency to vibration or unsteadiness. The pieces of which it is composed should be of good deal, 1¼ inch thick, and from 3½ to 4½ inches wide, according to circumstances, that is to say, according to the weights which it has to carry. The essential points are these, namely, that the keys, or manual, shall rest upon firm supports at the proper height above the floor; that the sound-board shall be borne upon bearers at a sufficient height above the keys to admit the intervening mechanism; that the bellows shall be carried on cross pieces far enough removed from the floor to admit of the free play of the feeder.

You will take into consideration, in designing your frame, the question whether you will have pedals, and the still more important question whether you will have separate pipes for them, and how they are to be connected with the lower keys. Room must be provided for all the apparatus involved in these arrangements, and, as in every part of our work, so in this, we say that the reader himself must think over carefully all contingencies, and make a preliminary drawing to scale for his own guidance.

Enough if we lay down here the following rules:—