ESSENTIAL QUALITIES.
Every American bicycle has individualities of its own, and especially in the running gear. No clearances have been allowed, and it is simply out of the question to attach the foreign type of case unless the bicycle is built for it. However, in some instances, bicycles were made with that end in view and the cases were attached, but American riders found that their unsightliness, excessive weight and inefficiency made them more of a nuisance than a help, and the gear case came into public disfavor. However, in spite of these discouragements, the necessity of a clean chain appealed so strongly to an American mechanic that, without any knowledge of the gear case constructions of Europe, he set to work to devise a method of thoroughly protecting the chain, and during the season of ’96 made many experiments to ascertain the construction that could be successfully applied to American bicycles and appeal to American riders. The study of road conditions showed that a gear case must be not simply a protection for mud, but every joint must be dust-tight and rain-proof. In a country like England, where mud is the prevailing condition, these absolutely tight joints are not so essential, but in this country they took first place. Again, the case must have good appearance and be comparatively light in weight, and, as the worst problem of all, it must be adaptable to some few hundred distinct makes of bicycles, no two of them alike in the running gear.
CLEVELAND
GEAR CASE.
The inventor started with the idea of covering the chain with an endless rubber tube, which should be split in its inner length and run with the chain. As it reached the sprockets it would be separated by a separator and follow around the sprocket over the chain, clinging to either side of the sprocket. This was theoretically a very good idea, but in practice developed many serious objections. In the first place, the tube was liable to catch between chain and sprocket teeth. It increased the friction of the machine and could not be made to be of very long life. It was also neither dust nor rain tight, and proved a nuisance instead of a blessing. Still following up the idea of utilizing rubber, a case was devised having rubber chain runs with rubber box over front and rear sprocket, this rubber box suitably supported by metallic parts. The only objection to this was the quick wearing out of the chain runs by the constant friction of the chain. Still retaining the rubber boxes, light metallic chain runs were substituted for the rubber, and it was then found that an ideal construction as regards strength and tightness of joints was obtained. These cases were put in public use after being exhibited at the Chicago and New York cycle shows of 1897, and have been sold and used quite extensively during the past season. They have been very much improved, so that all objections to the early models have been completely done away with, and today an American gear case, known as the Frost, is to be had upon any first class ’98 bicycle, being offered by nearly every bicycle maker. As it can be attached to old bicycles, there is no reason why every rider cannot have an up-to-date feature, with the comfort and pleasure assured by a clean chain. It has been actually proven that they will stand driving rains, snow storms, blizzards, dust storms, constant use on the dustiest of roads, and, in fact, have proven absolutely impervious to all foreign substances, keeping the chain and running gear perfectly clean and in condition for an entire season without any attention being given.
These desirable features are obtained by the use of an elastic rubber joint, the case itself being built of steel, but all the joints closed with this soft elastic rubber, on the same principle as a rubber gas tube is connected with a fixture. This case, to look at, is very compact and solid, but it can be almost instantly separated, either for changing sprockets, getting at the chain, or removing rear wheel. The operation is very brief, and even that has to be gone through with seldom a change of tires or renewal of broken spokes being almost the only occasion for separating the case. The chain can be taken out if desired, but as a matter of fact one always forgets that there is a chain when riding the “Enclosed Chain Model,” as this construction is now called.
CHAPTER VI.
THE CHAIN AND ITS FUNCTIONS.
There are few, if any, parts of the modern bicycle that have played a more important rôle in its development, than has the chain, and yet it is safe to say that there is no part of the vehicle to which the average rider pays less attention, save to occasionally clean it of its accumulated impediments, or which he understands so little.
BROWN
ROLLER SPROCKET.
Every rider, of course, understands how important is the office of the chain in the propulsion of his wheel—that without it his machine is an utterly useless structure of metal, wood and rubber. As to its parts, however, and their relation to one another, he is oftener than not carelessly indifferent. While as to the mechanical skill and genius that has overcome, one by one, the past difficulties of chain and sprocket propulsion, as applied to the bicycle, bringing it in the end, to its present state of perfection, he is wholly uninformed. Many riders have been inconvenienced and annoyed to the extent of exasperation, upon discovering that “something was wrong” about their wheels. Just what, they have been utterly at a loss to tell or understand, but the fact has remained that “something was wrong,” and so, cutting their rides short, they have despatched their wheel forthwith to the repair shop. Had they known, as the repair man knew, that it was their own lack of familiarity and consequent sense of appreciation of that apparently simple, yet sensitive part of their machines—the chain, to which their misfortunes were due, how great would have been their astonishment.
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.
To arrange the lines of gear teeth, either straight or by various gentle curves, so that when the teeth are in operation they will close together and then separate with a rolling motion, with no slipping or grinding, with no friction, has been a mechanical problem for a hundred years. This has not been accomplished on the bevel geared chainless bicycle, and it can never be fully accomplished anywhere. Press the palms of your hands together firmly, then slide one hand off the other while so pressed—that is rubbing friction; now lay the backs of your hands together, pressing as before, and roll them away from each other until they part at the ends of the fingers. That is rolling friction, and if we could only manage to make gears and other contacting surfaces in machinery meet and part company exactly thus, we could avoid friction almost altogether.