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.
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.