The following text may have been generated by Optical Character Recognition, with varying degrees of accuracy. Reader beware!

278 nett, THE MARINE REVIEW FIG. 9--THE HUGE PLANER ON WHICH THIS LOW PRESSURE VALVE-SEAT FACE IS PLANED WILL TAKE WORK 13 FEET BETWEEN THE HOUSINGS--IN THIS ILLUSTRATION THE - FINISHING CHIP IS BEING TAKEN for the crosshead guides, the top which fastens to the cylinders and bosses for the reverse shaft brackets, etc. The surfaces requiring the most careful finishing are the upper and lower ends and the seat for the cross- head guides. It is obvious that the upper and lower ends must be paral- lel to insure correct assembly as these units connect the cylinders with the bed plate. Again, the seat for the crosshead guides must be true to insure correct alignment between the crosshead and piston travel. After planing, the various holes for bolts and dowel pins are drilled, reamed and tapped which completes the ma- chining operations on these parts. Among the most important units to machine are the cylinders, for on the accuracy of these members de- pends to a great degree the econom- ical working of the finished engine. It is obvious that a true-bored cylin- der is economical in steam consump- pressure cylinder is to bore it. tion while one that is bored egg- shaped, which sometimes happens, per- mits live steam to escape past the piston and into the exhaust without performing any work. 'he: frst low These cylinders are not equipped with lin- ers and as it is practicable to bore them first, any imperfections in the casting will show up before a large amount of time has been spent in planing operations. The operation of boring a low pressure cylinder is shown in Fig. 11. This work is done on a _ 16-30-foot convertible boring mill and requires 36 hours. The ends of the cylinder are also faced during this operation. In Fie 1. the counterbored section has been roughed out and a roughing chip started down the cylinder. The ob- ject of boring the cylinders on a ver- tical mill is to insure them being round when assembled. A cylinder operation on the June, 1919 bored on a _ horizontal boring mit might show up egg-shaped when as. sembled in a vertical position. Cop. 'versely, cylinders for horizontal ep. gines are generally bored on a hori- zontal boring mill. The boring mit used for this operation is rigid jp construction which factor is necessary to avoid chattering. The finishing cyt is taken with a wide feed which in- sures the sides of the cylinder wal] being parallel within close limits. Considerable care must be exercised in setting up the casting for the in- itial operation to make sure that. all surfaces requiring machining will clean up, for while the amount allowed on the casting for finishing is liberal, care- lessness in handling large castings in setting them up for machining op- erations would result in some syr- faces not finishing out. Thus careful setting is necessary before the cut- ting tools are brought in operation. The next operation on the low- pressure cylinder is to plane the seat for the supplementary valve face. These cylinders are supplied with supplementary valve faces to insure economical repairs when the face be- comes badly worn through use. It would necessitate dismantling 'the en- gine to refinish the valve face if it were made integral with the casting. In the present case, however, all that is necessary is to remove the supplemen- tary face, refinish it and replace it. Tf the face is too badly worn for refinishing, a new one is readily sub- stituted. The supplementary face is held in .place with bronze screws. The operation of planing the seat is shown in Fig. 9. This work is done on a planer that will take work 13° feet square between the housings. The platen of this planer weighs 50 tons and the reversal is done elec- trically. It is necessary to plane the seat flat, otherwise the valve seat would require unnecessary scraping to insure a good fit. After all the surfaces that require planing are fin- ished, the next operation is to drill the holes for the steam chest cover and the supplementary valve seat serews. This work is done om 4 radial drill and is illustrated in Fig. 10. Exact duplication of parts is as- sured by using drilling jigs. As the illustration shows, a jig is fastened on the upper surface of the casting for locating holes for the steam-chest cover studs while the jig shown in a lower position is for drilling the holes for the supplementary valve seat. The casting is blocked up on the drill base and' is squared up by the finished ends. Holes in the lower end of the cylinder are sometimes machined on a horizontal boring mill. This is shown at the right in Fig. 12.