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76 true by emery or corundum wheels. Beyond removing the sharp edges no fitters’ work is required, and the bars go straight to the erecting shop. The type of grinding machine used is quite different from that employed for grinding piston rods, and may be likened to a planing machine, in which cutting tools are replaced by an abrasive wheel.

Connecting and Coupling Rods. The machining of connecting and coupling rods is a case in which large milling machines have replaced planing machines. The rods are now fluted out to form an I-section, and the whole of the surfaces and edges are milled. Fig. 40 shows the surfaces of two rods being milled on a large machine. In the ordinary type of connecting rod the brasses must be bedded down and fitted into the straps, and the straps fitted to the rods, etc., so that there is no shake, and the rod works as if it were a solid piece. The rod must be straight, and the holes through the brasses, in which the crank and crosshead pins work, must be at right angles to the axis of the rod, and the axes of both holes parallel to each other. Such work has to be done by the fitters when putting the various pieces of the rods together, before sending them to the erecting shop.

Coupling rods in this country are not fitted with adjustable brasses like connecting rods, but have plain circular bushes lined with white metal. On the Great Western Railway the