It is with a thorough appreciation of how large a percentage of the wheelman’s misfortunes are chargeable to a lack of knowledge of chain construction and action, that the writer has deemed the subject one well worthy of special treatment in these columns. That many readers will admit, after perusal, that however well they may have understood their wheels in other and less important parts, they still had much to learn of its most vital and intricate parts, is altogether likely.
A study of cycle chain construction will show the regulation chain to be, simply speaking, an endless belt provided with holes which engage projections on a form of pulley called a sprocket. It is composed of blocks alternating with and joined by a pair of links or side-plates; the blocks drop down into the spaces between the teeth on the sprocket, and those teeth come up through the spaces or openings between each two side links, these links of course holding the whole together by pins through their ends.
The “pitch” of a sprocket, as of any toothed wheel, means usually the number of teeth cut upon it for each inch of its diameter. The “pitch-line” is circumferential, though not at the extreme ends of the teeth; it is the line where the teeth of two engaging gear wheels come together, or the line passing through the contact or acting surfaces of the teeth. As a chain lies on the sprockets, this pitch line passes almost exactly through the centre of the teeth, and the rivets of the chain.
CHANTRELL CHAINS.
To speak of a chain as “one-quarter-inch” or as a “three-sixteenths chain” means that such is its measure in width between the plates of the links. This is also the thickness of the sprocket, barring a very slight difference to prevent too tight a fit. To speak of a chain as having an “inch pitch” (which is the regular standard in this country) means that the distance between the centres of the spaces through which the sprocket teeth come (as above stated) is one inch, and of course the same measurement applies to the sprocket; the spaces on that, measured between the centres of two adjacent teeth, must be an inch. It is plain that sprocket and chain must correspond in order to work properly. A chain of a half-inch pitch would not fit a sprocket of one-inch pitch, or vice versa. If the chain were made just a little too “long,” it might go part way around the sprocket, but a disagreement would soon be found. It is charged against the chain, and correctly, that use (helped by dirt under the condition of being uncovered) wears chain and sprocket both, so that they gradually cease to match together, as at first. When this occurs, the chain is said to be “out of pitch.” On the other hand, a chain will work a long time and very well after it has considerably lost its first exactness of fit, whereas gears which have worn grind and complain dismally.
KEATING
TWIN-ROLLER.