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Cee ESO july, 1919 on a horizontal boring mill. This is an important operation due to the fact that this hole must stand parallel with the bottom surface of the T-end. Otherwise, it is necessary to spring the rod in the assembling operation to make it align properly, which pro- cedure is generally unsatisfactory. Whenever possible, many parts are machined at-one setting. A good ex- ample of this.is shown in Fig. 17. In this instance ,the parts are reverse- shaft brackets...Under ordinary condi- tions, these pieces would be machined one ata time, a procedure which in- volves considerable time in setting up operations. By locating several at one time on the planer, unnecessary work is avoided. At one setting these pieces are planed on the surface that locates them on the engine columns, and at one side. Then they are turned over and the other side finished. The bear- ing for the caps is next planed. After the caps are in place, the brackets are bored to receive the reverse shaft. This work is done on the vertical boring mill. The valve stems are steel forgings. They are first carefully turned to size in the lathe. Next, the lower ends are finished .on the shaper... This end carries a split bushing which fits over the turned part of the link block. The bushing is held in.place through the medium of a cap. Accurate Lathe Work Involved The piston rods also are: steel forg- ings, so designed that the high: pres- sure, low pressure. and intermediate rods are interchangeable. As piston rods are comparatively bulky spare parts to carry aboard ship, this feature of interchangeability saves space. The rods are turned to size in the: lathe. The first operation consists of taking a roughing cut over the entire rod, after which the tapered portions that engage the crosshead and piston are turned. Next, the threads at each end are cut. This operation is fol- lowed by finish turning both tapered portions. An accurate ring gage is used to insure turning the correct taper in this operation. The last ma- chining operation consists of taking _ the finishing cut over the body of the piston. This is an important step because the rod must be round 'and parallel. Otherwise, steam would blow past the packing. The work is sized with micrometers and then carefully polished. . The crosshead guides are cast iron, bolted to the engine columns. These are provisioned for water cooling. They are carefully finished by plan- ing by ordinary methods. It is neces- sary that this work be carefully car- curately on the flat ried out 'because the finished guides must be both flat and smooth to form 'an adequate bearing for the crosshead slippers. The crank and wrist pin boxes. are steel castings lined with bearing met- al. These pieces are first planed ac- surfaces after which they are lined with bearing metal. The holes are next bored in the vertical boring mill. The main bearings for the crank- shaft are cast iron. These are care- fully planed to fit recesses in the bed plate after which the bearing metal is cast in place. The holes are then bored in the vertical boring mill. The crosshead is a steel forging. It is first planed to accommodate the slippers and then bored to fit the THE MARINE REVIEW 343 size. Next the grooves for the rings are: Cit: The packing rings that fit these grooves are turned and bored, sev- eral at a time, in the vertical boring mill by the same methods previously described in machining piston rings. The low-pressure valve is planed on its wearing surface and then machined to fit its stem. Next, the recess at the back for the accommodation of the balance ring is machined. This ring bears on a cast-iron balance plate, the object of this feature being to semibalance the valve. The balanc- ing mechanism calls for accurate ma- chining for if this is not properly carried out, leakage results which renders the semibalancing feature of little value. This throws an enormous : i FIG. 20--MILLING 40 AIR PUMP BEARINGS AT ONE SETTING ON A LARGE HORIZONTAL® MILLING MACHINE wrist pin. The taper hole, for locat- ing the piston in place, is. bored next. It is essential that the two. bored holes stand exactly square with each other to insure proper functioning after assembly. Gages are used in sizing the holes to insure duplication of parts. The crosshead slippers are cast iron lined with bearing metal. These are first planed to size after which the metal is cast in place. . This is then carefully machined to. insure a good bearing on the crosshead guide. The slippers. are bolted to the crosshead, provision being made for adjustment for wear. All the valves are cast iron. . The high-pressure and intermediate valves are of the piston type while the low pressure valve is of the double-ported, plain slide valve. type. The piston valves are first. bored. to fit the valve stems and then- accurately turned to load on the valve gear due to the large area of 'the valve in contact with its seat. ; In addition to the above major machining operations, there are a number of minor features. All ma- chining operations are carried 'out with care. to make sure that the finished parts will fit properly in assembly Jigs and fixtures are used whenever possible. Government specifications state that all materials and workmanship are to be the best for the purposes in- tended and that all wearing parts must be accurately machined. All flanges conform to the American Society of Mechanical Engineers' standard. (To be concluded) The New York & Porto Rico Steam- ship Co. has disposed of its interest in the steamer BEeRwinpd to the govern- ment for $475,000.