Making a Gas Brazing Hearth.
—The brazing hearth can be bought ready-made, or can be cheaply put together by the worker himself, the necessary materials consisting of two bellows, some lead piping, and an old packing case to support a large size frying-pan—about 1 ft. 4 in. by 1 ft. The bellows are fixed one above the other, interconnected by a fixed lead pipe, one pair of bellows worked by the foot pumping air into the pair above it, from which the air is taken to a bunsen blast burner by flexible tube. This bunsen burner can also be easily and cheaply made, and as this works very well and will be found useful for both soldering and brazing, the following hints on making it are given. First, get two ordinary large house bellows about 1 ft. square, or larger if possible; the larger the better. Next a good strong packing case about 2 ft. long by 1 ft. 3 in. high and 10 in. wide is required. One end of the box will form the base, and to make it steadier two 1-in. boards should be screwed across to protrude about 6 in. on each side, the front one being considerably wider, as can be seen at T ([Fig. 62]), which shows the apparatus with one of the case sides removed. The packing case proper is denoted by the letter A; the part A S A was formerly the bottom of the case, but is now the back; and the top A V A was the end of the packing case. Half-way between the top and bottom a shelf B should be fixed, having a large hole cut out of the middle at G to accommodate the union piece (seen in section), which holds the lead air-pipe communicating from the lower bellows to the upper.
Fig. 62.—Home-made Brazing Hearth
In the back, near the bottom, at S, cut a hole for the nozzle of one of the bellows, and above the shelf cut another hole at S1 to take the nozzle of the other bellows. The bottom bellows C should have the top handle extended by a piece of stout bent iron N to act as a pedal, and should be screwed to the base. A central hole about 3 in. in diameter should be cut at P to allow the air to reach the valve. Now get a piece of lead pipe 1⁄2 in. inside diameter, and, having cut down the nozzle to just under that diameter, force the mouth of the pipe over it as at S, and bend the pipe F as shown, to reach the centre of the shelf B and enter the hole G until flush with the top. Remove the lead pipe and get a block of wood about 3 in. square. Cut off the corners and bore a hole in the middle, so that the lead pipe will just pass through it, and countersink the hole. Broach out the mouth of the lead pipe until it becomes bell-shaped and fits the block of wood, so that its edge is flush with the wood when pressed hard against it. This is clearly shown at G, where the dark shading represents the wood block. Cut a leather washer the size of the block, with a 1⁄2-in. central hole, and lay this over the hole in the bottom of the top bellows where the leather flap valve is. Bore two holes in the wood block, and screw this down tightly to the bottom of the bellows, so that the bell-mouth of the lead pipe faces the hole and has the leather between it and the block. This should make an air-tight joint for the fixing of the pipe to the bellows.
Next, push the nozzle of the bellows through the hole S1, and screw the bellows down tightly to the shelf B. Join the lead pipe to the nozzle of the bottom bellows, and make an air-tight joint with glue and tape bound round. Between the top of the upper bellows D and the top of the packing case at V, a stout sofa spring E is fixed to keep the top bellows shut down tight till air is pumped in from the bellows below.
From a screw near the top of the case stretch a house-bell coil spring M, and attach its lower end to the foot-plate or pedal N. This spring tends to keep the lower bellows open. When pressure is put on the foot-plate N, air is pumped from the lower to the upper bellows, and thence along the flexible pipe R to the bunsen blast nozzle described in detail later. If it were not for the upper bellows, the air would come to the nozzle in puffs, but the spring E keeps the pressure constant, and a steady blast is secured. The rubber pipe R should be of sufficient length to reach the hand conveniently, and allow room for movement.
The hearth K can be made from sheet-metal, with the edges bent upwards to form a tray; or an old frying-pan will answer very well. Whichever is employed, four iron stays or legs H must be used to raise it above the top of the packing case as shown. These legs should be screwed at one end to the sides of the case, and at the other to the pan, and if a frying-pan is used, the handle may be cut and bent to form a hook as at L; it then acts as a support for the blast nozzle.
Fig. 63.—Blowpipe or Blast Gas Nozzle
for Brazing Hearth
For use with the brazing hearth, a blast gas nozzle on the bunsen principle is required, and this is easily made from two pieces of gas-piping, a right-angle joint, and two mouthpieces to take flexible pipes. First, get 1 ft. of 3⁄4-in. brass (or iron) pipe and an elbow, internally threaded at both ends. Cut 2 in. off the brass pipe, and cut a thread at one end of the short piece and one end of the long piece, to screw into the elbow as shown in [Fig. 63]. At the other end of the long tube solder in a cock or mouthpiece to take a large diameter flexible pipe from the gas bracket. Next get 1 ft. of 1⁄4-in. brass pipe, and bend it to the shape shown at B, soldering a mouthpiece at F to take the smaller diameter air-pipe R ([Fig. 62]) from the bellows. Bore a hole through the elbow C, and push the pipe in, making a tight fit, and so that it passes centrally through the larger brass tube until it nearly reaches the end as shown at D. Run a shoulder of solder to hold the small tube firmly in the larger one as at E, and unite with a drop of solder the large tube A and the small tube B where they cross at G.
The gas passes up the large pipe, and out at D, and a blast of air is forced through the centre of the flame through the small pipe B. The shape of the small pipe allows of it being readily hung up on the hook L ([Fig. 62]) when not in use. Instead of the mouthpiece shown at H ([Fig. 63]), a cock will be found more convenient; but it should not be too small, or it will restrict the flow of gas, which should be as great as possible. No gas-cock should have less than 1⁄4-in hole.
The “fuel” (heat conservers) consists of chunks or cubes of asbestos, and when these are blown upon with the gas flame, the heat is quite sufficient for moderately heavy brazing. Be careful not to get any kinks in the flexible tubes, or the air and gas will be reduced in quantity, if not stopped altogether.
A square of thick asbestos (sheet) is useful for laying on small articles whilst brazing, and a piece or two of charcoal will be handy for silver-soldering.