Page:Steamlocomotivec00ahrorich.djvu/92

 connecting rod big-ends are made with similar bushes, which are much simpler, and are stated to wear well for a long period.

Link Motion.—The link motion, consists of a large number of parts which have to be machined and fitted together. The side faces of the curved quadrant links are planed or milled to the proper thickness, several being machined at one time. A template is then laid on them and each marked off to the proper finished curved shape. All the holes are drilled through “jigs” which locate them accurately, and the links are slotted out to the lines marked by the template. The blocks which work in the quadrant link are also slotted or milled to shape. The levers which connect the various parts of the link motion are milled on the faces and to contour on the sides. All work of this kind is produced in a better manner and in less time on milling machines than by slotting and planing. All holes and the pins which fit into them are bored and turned to limit gauges. The fitters then fit all the parts together, testing and levelling them so that everything is perfectly “square,” and all the necessary oil grooves are cut in the blocks and pin holes.

Case-Hardening. The parts of the link motion are then taken apart and sent to the case-hardening shop, a department which has not so far been