The Modern Bicycle and Its Accessories

by Alex Schwalbach; Julius Wilcox

THE QUESTION OF “POINTS” OF CONTACT

The ball may be regarded as a number of tiny thin wheels or disks, borne on a common axis. Obviously, the larger the wheel the more easily it will roll; hence we reach the first rule, namely: the ball should rest and roll on its largest diameter, if possible, and, as a corollary, large balls (within reasonable limits) are better than small ones. In order to fully carry out this rule and use the largest diameter, the ball must be placed between two plain cylinders or rings, and the weight must bear in a direction at right angles to the plain surfaces; the ball will then roll at its best, and yet this construction is not practicable. This is so because there would be no means of keeping the balls in one track and because the surfaces and the balls would not stay in contact, there being no “adjustability” or means of moving them closer together. Coming, then, to the usual construction of a fixed axle having on it a stationary cone, and a wheel hub revolving about this, we reach the important practical but not half-considered question of “points.” That is, on how many points in its surface shall the ball rest? The hub is commonly called the “case” or the “cup.” If the ball rests on the cup at one spot and on the cone at another, the bearing is called “two-point,” or “spot” is more nearly accurate than “point,” if by the latter the literal mathematical point is meant; if the ball rests on the cup at two places and on the cone at one, the bearing is called “three point;” if the ball rests at two places on cup and cone both, the bearing is called “four point.”

OLD DOUBLE-ROW
BALL BEARING.

Referring to the cut of the two-point, it is plain that one of the coned surfaces shown, revolving in a plane at right angles with the axle, must roll the ball on the other cone, the ball running on both in planes parallel to the plane of motion of the revolving cone, as is indicated by the dotted lines; hence the ball will roll, and not slip or slide. To a very limited extent the two-point bearing has been used in this country. We can at the moment name only one make which we are sure has had this form really so made, and well made, with the surfaces accurately curved so as to place the balls correctly and with grinding after shaping. This make is the Humber, which deserves honorable mention for the importance attached to the bearings and for the intelligent care with which they have been constructed. This remark, however, is by no means meant as exclusive or as implying that no other makes have excellent bearings.

LOWER HALF OF
DOUBLE-ROW
BALL BEARING.

An interesting form of two-point bearing is the Lake, made by the C. S. Caffrey Company of Camden, N. J. It makes the coned faces of cone and cup parallel and flat, inclined at an angle of 45 degrees to the axle. Here it is evident that the ball will run without twisting or skewing, and in order to keep the balls in place the old device of putting them in a perforated loose ring is employed. The holes in this ring for the balls are made oval instead of round, in what does not seem a very well grounded expectation of thus removing the slight friction between ball and ring. The holes are also “staggered,” so that the balls do not run on exactly the same tracks. It is claimed that, on a test, a front wheel with this bearing, being whirled by the hand, ran an hour and five minutes. This must be admitted to be a remarkable performance, even if the adjustment were loose.

Far the commonest construction, however, has been the three-point, partly because, by a confusion of ideas, a three-point bearing has seemed as if it must be firmer than a two-point, and partly because the former can be turned out at a very moderate cost. As in almost universal use during several years past, and as produced by the parts-makers almost without exception, the form of this is as shown in the cut. ([See page 86].) Turn the page so as to bring the surface C on the cone horizontal, and if you then imagine this surface C in the same plane as line CD, it is easy to see that the ball will roll upon the case at A and B both; and as the diameters of the ball at A and B are equal, it will roll around the circle easily and without skewing. As the inter-action of the parts is not changed thereby, we for the moment, as a matter of convenience, assume that the cup is stationary and the axle turns, which is the reverse of the fact. In actual position and working it is evident that under the weight of the load the ball will slip down the slope at C and be pressed hard against the side B as well as against the bottom A. The relative pressure on these two points will depend on the flatness or steepness of the surface C, but ordinarily the pressure on the two will be nearly equal. The action at C tries to roll the ball on a horizontal axis, parallel with the wheel axle; the action of B upon the ball tries to roll it on a vertical axis, parallel with CC. Moved by C, the ball may roll on A and slide on B, or it may stick fast to C and slide on A and B both, or it may stick fast to both A and B and slide on C. Certainly it cannot have more than one of these movements at any time, and hence the ball cannot possibly roll in two directions at once.

To make this more clear, imagine the ball and the two surfaces to be toothed where they come in contact, thus being visibly gear wheels; if these teeth are spur-teeth, the cone will impel the ball in its own plane of motion, namely, line CC, and the ball will then roll on side A and rub on side B; if the teeth are bevel, the ball will roll on B and rub on A.

“FOUR-POINT” BEARING— TWO POSSIBLE FORMS.	ACTUAL “FOUR-POINT” BEARING— “E AND D” PATTERN.