This section is from the book "Cassell's Cyclopaedia Of Mechanics", by Paul N. Hasluck. Also available from Amazon: Cassell's Cyclopaedia Of Mechanics.
Here are given full instructions on casting and finishing small brass gas-cocks. The patterns may be of wood or brass, but brass is to be preferred, as it wears much better than wood. Core prints must be turned on the ends of the patterns so that, when moulded, places will be left in the mould in which to insert the core. The patterns must be made sufficiently large to allow for shrinkage and for the metal turned oft' in finishing. The ends of the core patterns must be exactly the same size as the core print on the brass pattern. Core stocks for each of the cores must be made. The keys may be made in the same manner as the body of the casting. Figs. I to 1 give views of the body of the cock and the key in two positions. The key must be sufficiently large to turn down for grinding. Make the moulds, trim tnem, and they will be ready for finishing. In finishing the cock, use an iron bell chuck or an ordinary brass-turner's chuck. Turn one end of the cock square, and thread the hole with a suitable sized thread. Repeat the operation at the other end of the cock. Skim the cock all over, and face both ends of the key way. Then turn the hole for the key slightly taper as cast.
Now skim the outside of the key casting on the taper similar to that of the hole in the cock, and press the cock on. If it does not go on as it should, skim a little more till it is correct. Square the end off, drill a hole up it, and thread with a screw to curry the small brass screw that holds on the D washer, to prevent the tap being pulled off and to obviate the escape of gas. Each tap must be turned to each cock, and must be left in it till ground; this will save time and waste. In grinding in, fix the tap in the chuck, place a little loam and water on it, and press on the cock. This will cause the loam to grind down the surface of the key and make a good joint. The common test applied by the workman is to draw out all air by the tongue and mouth, when the cock will, if sound, adhere to the tongue. The key must have a round hole drilled through it, and at the top should be inserted a pin, which catches on the top of the cock and prevents its being turned more than halfway round. In making the sand core, insert a piece of thin iron wire through lengthwise; this will strengthen the core (see Fig. 4). The cores in each case must be made to suit the purpose, and will depend on the size and nature of the cock in hand.
Making Brass Gas-cocks.