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Jane, 1979 Intermediate cylinders require two boring operations which are done on the vertical boring mill. These are the bores for the cylinder and piston valve. In the case of this cylinder, the planing operations are finished before boring..' The high-pressure cylinder also requires two boring op- erations, one for the cylinder bore and the other for the piston valve. These cylinders are bored to fit chilled iron liners to take the wear. Thus, in- stead of reboring them when worn, the worn liners are forced out and new ones substituted. The bore for the cylinder is machined on the ver- tical boring mill but in the case of the piston-valve bore, the work is done on a horizontal boring mill. This is necessary because the limited size of the hole will not permit the' entrance of the type of boring bar with which the vertical mill is equipped. The operation of boring the piston valve seat is shown in Fig. 8. The machine used in this case is a special boring mill built for stationary-engine work which carries two boring bars set at 90 degrees. Cylinder heads and pistons are turned and bored on vertical boring mills. As this is a simple vertical mill turning operation it is prosecuted by methods known to every mechanic. Piston rings are also turned on ver- tical boring mills as by this means it is an easy matter to turn the out- side and bore the inside at one opera- tion, using two boring bars simul- taneously. In turning large piston rings by this method, that is, locating them vertically, round rings are as- sured which might not always be possible if the work were done hori- zontally. The piston rings are made sufficiently large to allow for making a satisfactory fit after they are split. The crankshaft of any marine en- gine is an important member as this unit is the vital connecting medium by which the reciprocating motion of the pistons is conveyed to the propeller shaft. The crankshaft of the engine under discussion is of the built-up type made in two. units, bolted together through the medium of coupling flanges. One section car- ries the high-pressure and intermediate cranks while the other accommodates the low-pressure crank. The shafts and pins are forged steel while the webs, or cranks as they are sometimes called, are steel cast- ings which are positioned by keys and firmly held in 'place by being shrunk on over the shafts and pins. As stated before, the pins are cranked at 120 degrees. The couplings are forged integral with the shaft units. The first step in machining the webs is to surface them accurately THE MARINE REVIEW FIG. 10--LARGE DRILLING JIGS INSURE EXACT DUPLICATION OF FINISHED UNITS--IN THIS CASE THE OPERATION IS DRILLING HOLES FOR THE LOW-PRESSURE STEAM CHEST COVER, ON A RADIAL DRILL for upon the skill with which this operation is carried out depends the accuracy of the finished shaft. It is obvious that the front and back sur- faces, or cheeks, must be _ parallel, as these surfaces are used as locating points shafts and pins. The webs are surfaced on the planer as illustrated in Fig. 7. This tool is equipped with two heads on the cross rail and a side head. The side head, however, is not utilized in this opera- tion. This planer has ample capaci- ty for the work in question as it will clear 60 inches between the hous- ings. Six webs are planed at one operation. They are held in place on the platen by means of special holding fixtures equipped with locat- ing bolts. These bolts are set at an angle which causes them to force the work -downward, toward the platen. This insures a flat contact. The hold- ing fixtures are securely bolted to the in boring the holes for the - limits. platen and as they are designed par- tially to encircle the ends of the webs, the danger of the work "floating away" from its setting, due to the contact of the tool while taking a heavy cut, is eliminated. In Fig. 7, a roughing cut is in progress. The feed is 1/32-inch wide while the depth of cut is 13/16-inch. The webs are first roughed out on each side after which two finish- ing cuts are taken, one on either side. Customary methods of measuring large work of this: description, such as spring calipers, a scale or surface gage, are not deemed accurate enough © for this work. The pieces are cali- | pered with micrometers to make sure -- that they are parallel within close The next operation is to bore the holes for the safts and pins. This work is done on a vertical boring mill. Two webs that are to form one crank are positioned together and Lee?