Remark.—These figures, however, must be understood rather as illustrations of our meaning than as representations of actual work.
Conveyancing tubes are in constant use, not only as substitutes for grooving, but as ancillary to it. They are made of pipe-metal, and from about ⅝ inch in diameter to much larger sizes. To manage them neatly and well you should be adroit in the use of the soldering-iron. They are commonly smeared over with a composition which will not receive the melted solder; this composition is scraped off at the points where a junction is to be made at an angle, and with the usual copper tool, a little resin and tallow, the solder is applied. Much practice is needed to give mastery of this process, apparently so easy; we have known instances in which it has been avoided altogether by covering the junctions of the conductors with white leather secured by thick flour paste. It is right, also, to add, that we have seen successful conveyances made of cartridge paper rolled upon wooden mandrels with paste. Any tin-plate worker in your town or village would make them of his own material or of zinc, and in an hour or two would solder all the junctions for you when you had planned your arrangement thoroughly.
Assuming, however, the use of the usual tubes, we may say that they are thus applied. Let us suppose that the large pipe shown in Fig. 10 is to be conducted off from the sound-board at the higher level to the plank on which it stands. Bore the hole in the upper board a trifle larger than the outside diameter of the tube. Glue a patch of white leather over the hole, and cut out the aperture in this leather somewhat smaller than the hole, leaving an excess of leather all round the hole of about 1/8 inch. Then, making the end of the tube a little conical, thrust it into the hole; it will carry in with it the surplus margin of the leather, which will form around it an air-tight joint or collar. A right angle may be allowed in the tube at this first commencement at the hole itself, but in its subsequent course sharp corners should be avoided. The pipe is planted on a hole bored to a sufficient depth in a plank; a second hole, suited to a conducting tube, is bored at any convenient distance from this, and communication made between these two holes by a groove in the under side of the plank closed in with leather, parchment, thick paper, or wood; then the end of the tube is forced as before into the hole bored for it and provided with leather packing, and all is complete.
It is by these means that "speaking fronts" are arranged according to any design.
Remark.—If you have all your pipes, metal as well as wood, ready at hand, it might be well to pierce the rack-board and fit them in their places at this stage of the proceedings, because chips and dust are inseparable from the operation, and may be more troublesome and mischievous after the pallets are put in than now. Those readers who resolve on this course may turn, then, to the subsequent pages, in which they will find all the directions which are necessary for their guidance. For our own part, we prefer to continue in the next chapter our account of the mechanism of the sound-board.
We may further remark, that while the boring-tools are in use we may perhaps do wisely in piercing holes also for the screws which are to hold the upper boards down upon the sliders. If the planing has been perfectly true, about four pairs of screws should be enough for each upper board, and no extra screws should be required to force the boards into closer contact at any intermediate part. The screws should pass clear and easily through the holes in the boards, and should bite well in the table beneath. The heads of the screws should be let down below the level of the upper surface of the boards by counter-sinking, and it is a useful practice to mark the places of these screws on the rack-board as well, and to bore corresponding holes in this latter, in order that if hereafter a slider should be pinched too tightly between the upper board and table, the end of a long screw-driver may be introduced to ease it by slackening the screws without disturbing the pipes.
But we shall have to return to this part of our subject.