Abstract: A magnetic compass comprises a case having a transparent cover and a magnetic compass card having a hub, which is rotatably supported on a central shaft projecting up from the base of the case by bearings comprising a thrust bearing between the hub and the upper end of the shaft and a radial bearing between the hub and a portion of the shaft spaced downwardly from the upper end. The radial bearing comprises a bearing ring set in a central recess in the hub and a full circle of small balls between the bearing ring and the shaft. In one embodiment there are two such radial bearings located one below the other. The bearings rotatably support the compass card on the shaft and retain it approximately perpendicular to the shaft even if the case is tilted.

Abstract: Cylindrical or cubical blanks for producing balls, in particular small balls for ball bearings and placed in a vertical tube positioned eccentrically above a grinding disc having a horizontal plane abrasive upper surface which forms the bottom of the tube. The blanks partially fill the tube to a depth many times the cross section dimension of the blanks. For example many thousand of the blanks may be put in the tube at one time. The disc is then rotated to grind and tumble the blanks in the tube and to produce circulation of the blanks in the tube continually to bring different blanks into contact with the abrasive upper surface of the disc. During the grinding operation, a nozzle directs grinding fluid into the tube so as to promote circulation of the blanks in the tube and to inhibit the sticking of blanks to the side walls of the tube. In this manner all of the blanks in the tube are ground to approximately spherical shape.