EVOLUTION OF THE BEARING.
In cycle construction, the first bearing was the “plain” one in common use elsewhere; then a nicely fitted and hardened sleeve was added, and this was known as the “parallel” bearing. Rollers were also tried, but rollers have a determined habit of going askew, one end moving faster than the other, and as soon as they get out of parallel thus, they set up a great resistance. To meet this difficulty, the ends were sometimes made so as to overlap and match into one another, or the ends were loosely passed through thin rings, which revolved with the rollers around the axle; but the rollers still tried to run askew, and the efforts of the rings to prevent them caused another friction, so that the roller was abandoned. About the same time, the “adjustable cone” was tried. This was a male cone, threaded on the axle and fitting into a female coned space in the hub. The character of the rubbing action was not changed by this device, which was called a device to make wear in order that wear might be taken up, but the parts could obviously be kept in contact (though not in nice fit) by screwing the cone further in.
The next and final step was to interpose steel balls between these coned faces; and as the ball is a very short roller, with ends rounded off, it can go in any direction it pleases. The principle of lateral adjustment by moving a coned surface to or from another coned surface opposed thereto, with balls placed between, was patented more than twenty years ago and is still in universal use; yet, as just remarked, this is the adjustable cone modified. It is to be borne in mind that the only possible service of the cone, as before, is still to take up wear, and also that the retention of the cone for adjustment introduces new difficulties. Note also that on the old high “[Ordinary]” the large wheel had its bearing cases fixed and the axle revolving, because the power was applied to the axle, while the rear wheel had its axle fast and the wheel hubs revolved around it. On the modern bicycle the method reverses, both wheels revolving around fixed axles, while the crank shaft, which is the part receiving the driving power, revolves within a fixed bearing-case.
The revolving axle used to have two grooves, matching grooves within the fixed case, and the balls were held in holes in loosely fitting rings which slowly travelled around with them, these rings having no use except to aid while putting parts together. This double row bearing was called non-adjustable, because the sole way of tightening it up was to move the two halves of the bearing-case closer together; for this purpose the case was made in halves, as a “split lug,” and held by screw bolts. Yet this construction, if well made, solved the difficulty of the “points” in bearings and gave the balls a correct rolling motion.