OPERATION AND EVOLUTION OF THE CHAIN.
SOME ENGLISH CHAINS.
In considering the chain most people forget that although made up of many pieces of metal only a few are in action at a time. Only the upper half is in tension (the action is, of course, reversed in back-pedalling), and if the chain is opened and allowed to drop down it will for the moment act just the same. It is full of joints, but few are bending at any instant. As the chain runs upon the sprocket, its joints bend to conform to the circle, and they similarly bend back to an approximately straight line when leaving it. On the lower side, the joints bend easily; on the upper, they do so under tension. Press your thumb on the palm of the other hand, and, while pressing hard, draw it off; this gives some idea of the rubbing friction when the chain block leaves the tooth against which it is pulling. There is also some rub on the tooth where the chain is coming on the sprocket; and unless it is avoided by devices to be presently described, there is a rubbing between the tooth and the ends of the bending links, as well as within the joints themselves when they bend under pull. The effect of this friction is shown in the wear which comes on portions of the teeth; it also shows by flat places worn on the chain blocks, and the wear within the joints causes what is called “stretch,” the chain appearing to have grown longer. In a very slight degree there is a yielding between the parts which is called “set,” parts which are already in contact being pressed into still closer contact; this “set” supplies the trifle of elasticity, already mentioned, which tends to save the chain from fracture under heavy stress.
Chain and sprocket act on each other much as the teeth of gears act, and in effect they are a peculiar form of gears, for if you can imagine one of a pair of gear wheels flexible and flattened out like a chain, and thus running, it is evident that this action is really that of gearing. Chains were used on the tricycle before they were required for bicycles, and as long ago as 1881 there was a substitute attempted which was described thus: “The Queen driving bands are made very thin and neat, of a compound of silk and other strong substances, and are substituted for chains to save both weight, noise, and appearance.” The early chains were heavy and wide, at least ⅝-inch, and crudely made. The Ewart, as used on the Columbia Veloce ten years ago, was ingenious and simple; block and side-link were one, there was neither special joint nor rivet, and the chain could be opened at any point by turning it ([see cut on page 61]) and sliding to one side. Width of chain and thickness of sprocket gradually lessened; a few years ago, ¼ was the standard, but now it has settled to 3⁄16, even on tandems, and on racing wheels a ⅛ chain has been used in a few instances. The “B” chain has almost displaced the “8.”
DIAMOND “B.”
Quality of steel used, accuracy of pitch and fineness of fit and finish have steadily improved, and were never at so high a standard as in 1898; accuracy of cutting and scientific shaping of the sprocket teeth have also been constantly studied and show greater advance than ever, so that, as a result, the chains on this year’s product run with a smoothness and “sweetness” not before attained. The chainless movement has naturally contributed to this advance, which is a substantial fact. Quality has improved while cost of production and market price have declined, and the high-grade chain of 1898 may without extravagance of language be called “beautiful.” For instance, in a specimen before us the blocks are nickel steel, straw color, and the links are of bright tool steel; the inner edges of the links are chamfered or beveled to lessen the chance of the chain’s ever “mounting the sprocket” if it is run when too slack, and the ends of the pins are so perfectly headed that the operation has left no trace. This finely finished specimen happens to be from the Lefevre Arms Company of Syracuse, but like praise can be given to the best product of several other makers. As to strength, chains used to be made with a breaking strain as high as 1,800 pounds; we suppose the average with the narrower and lighter product of today is about 1,000 pounds, which is far beyond any driving strain it can receive.