ROLLERS.
Theoretically there is less friction in roller- than in ball-bearings, as there need be no sliding action whatever in the former if well made. But in actual practice no bearing can be made in which there is no tendency of the rollers to run together; and if we place them in a frame to hold them apart we shall have about as much friction as when they rub against one another. The most perfect plan is to place a small roller between each of the larger; with this arrangement the friction is practically nothing. The action of rollers upon the boxes is always a pure rolling friction, which cannot be the case with balls after the slightest groove is worn in the casing.
One reason for rollers being little used is that they tend to work out of line with the axle and box, which causes some ends to get a little in advance of the others, when they can no longer work perfectly. For an oscillating bearing,—that is, one that goes backward and forward, instead of continually around,—I have found rollers very good, since they cannot get much out of line; even when the bearing is a little imperfect, the rollers cannot multiply the imperfection, as they will in one that keeps going on in the same direction. The other great fault of the roller is its non-adjustability, although this can be rectified in the following way:
Roller construction.
The above cut shows a bearing and the construction lines that must be followed in its manufacture. The taper of the axle, roller, and box must all meet in a point, as at a; this arrangement is evident. The roller must be kept in proper position and roll around the large end in the same number of turns as the small end; hence the circumference of the small end of the roller must bear the same relation to the circumference of the larger as the relative ends of the axle and box bear to each other. The geometrical conditions are as follows: π being the relation of circumference to the diameter, referring to the diagram, we have b c : f g :: c d : g h :: b e : f i; hence π b c : π f g :: π c d : π g h :: π b e : π f i. Now, by virtue of the last formula, when the axle or box is revolved, each end of the roller will travel through exactly the same number of degrees around the axle and in the box, wherefore the axle rollers and box all keep straight.
CHAPTER XXI.
ALUMINUM IN CYCLE CONSTRUCTION—STRENGTH OF TUBES.
“We really thought that we were going to pass over a period of three months without having to chronicle the discovery (?) of a method of producing aluminum at a cost of not more than that of first-class steel. The periodical inventor has appeared, and this time he hails from Melrose, Mass., and his name is Washburn. Next!!”—Bicycling World.
Inventors do little harm in periodically making cheap aluminum or increasing its strength without adding to its gravity, but when a large corporation is started, as was done some months ago, with a lot of money and aluminum medals issued, the same being made out of copper, then the matter becomes serious. Probably, next to the hobby of separating water and creating enormous power thereby, the aluminum hobby holds undisputed sway. But as there really is something of interest to cyclists and cycle makers in the subject, there seems a need to touch upon it. Among the articles in the manufacture of which aluminum can be satisfactorily used we find in the catalogue of a well-known smelting firm mention made of bicycles, tricycles, etc. The idea exists in the minds of many that a bicycle made from pure aluminum would be a practical machine and much lighter than one of steel. This notion arises from the fact that aluminum in the pure state has a specific gravity of only 2.5, or about one-fourth the weight of steel. Below we print a letter from the Cowles Smelting and Aluminum Company on the subject.