forming threads before the lathe



The newly arrived stranger in India is generally struck with the fact that the screws of the country are all left-handed; that is to say, that on entering they do not turn like the hands of a watch, but in the opposite direction. These screws are not cut in a lathe or with what is called screwing tackle; they are made in the most primitive fashion by winding a piece of wire round a rod and soldering it in place. Suppose a screwed stopper is required for a water bottle of metal, the artificer takes wire of the desired size, doubles it, and winds it closely round the stopper, cutting it to the desired length. The two pieces of wire are then removed and one is soldered to the stopper, while the other is soldered inside the neck. Of course the stopper must be made of such a size that when the wire is wound round it, it will just enter the neck of the bottle. Such screws are always a bad fit, as they are made without regard to strength or wearing quality. This method of making screws in metal seems to have been the primitive one everywhere, and it is not many years since the “box” or long nut of vises in England was made in a similar manner. A piece of square rod, of a size to lie between the square thread of the screw, was carefully softened, cleaned, and bent round the screw, care being taken to make it as close a fit as possible. It was finally driven into the box while still on the screw, the screw was then removed, leaving the thread in its place in the box where it was brazed. A good deal of skill was required in the brazing so that the smallest amount of brass should be left in the box which was generally from 10 to 15 threads long. In India the vise is not an indigenous tool and is only used to a very moderate extent, and nuts for other purposes have often not more than one turn of effective thread. In cheap work, like the brass Kohl bottle made in great quantity in Delhi, it is considered sufficient to file a very rough screw thread on the stopper and to jam it into its place.

In the oldest iron work in India there is no sign of screws; bolts are all riveted, and nails that are meant to hold securely are clenched. The boat builder is not content with a clench equal to about three or four diameters of his nails; he will turn one ten to twelve diameters, regardless of the waste of good metal.

Of late years small screw-cutting lathes have become very popular among Indian craftsmen, who seem only to learn the use of the slide-rest and never that of the hand rest. They will make ½-inch studs on the lathe, although they may be made in half the time by hand, and of the use of the hand rest they have only the faintest notion. It is a common incident to see a brass turner squatting on an improvised table before his lathe, while a laborer treads for him or drives by means of a hand wheel. The screwing tackle of the English country blacksmith of fifty years ago would perfectly suit the ideas of the Indian workman. There were stocks and dies, and one tap tapering from 1¼ inches to 3/8 inch with a uniform thread. Being an unwieldy tool, small articles were applied to the tap which was fixed upright in a vise. Fortunately such tools no longer exist.

F. H. Colvin and F. A. Stanley, compilers.
Screw Thread Kinks.
New York: Hill Publishing, 1908.
Pages 96-99.


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