The mandrel should be lubricated before driving or pressing into the work to keep the surface from cutting. Fig. 3 shows one form of expanding mandrel. A cone man drel, Fig. 4, can be used in work that does not require great accuracy in being turned. An expanding mandrel for bored or cored work that is to be turned and faced is shown in Fig. 5. Large and long pipes, pedestals, and other hollow work can be held and centered by the center spider, Fig. 6. A spider is placed in each end of the hole, and the center a is adjusted by means of the screws b. The center of the work can be located within fairly close limits before the job is put on the lathe centers by using a ball hermaphrodite, Fig. 7. In using the spider mandrel, care must be taken not to spring the work out of round. A bridge b, Fig. 8, is usually cast across the end of a hole FIG. 6 FIG. 7 FIG. 8 cored in a heavy casting, and the center hole is placed in this bridge. Plug mandrels, or centers, as at a, Fig. 9, are driven into the b FIG. 9 a ends of a long cylindrical casting b such as piston valves with cored holes. The plugs may be turned from cast iron or steel, and the centers are located and drilled after the plugs are driven in place. Nut Arbor.-A nut arbor for holding a nut to be faced is shown in Fig. 10 with the nut in place. If the nut has not been tapped squarely and if it fits loosely on the arbor, it will first come against the shoulder at the point a. When this point touches, the nut will be rocked on the thread so that the axis of the nut thread will not be parallel to the axis of the arbor. If the nut should be faced while in this position, the face would not be true with the tapped thread. To overcome this, some form of equalizing washer, as shown in Figs. 11 and 12, is used. Chucks.-The three general classes of chucks are the independent chuck, the universal chuck, and the combination chuck. The independent chuck is the most useful for general work, as it will hold regular and irregular shapes. Rapid-acting universal chucks are ΠΡ FIG. 12 very useful for holding regular work, as they are self-centering. These chucks are not so accurate as the independent chuck, as they become untrue with wear. The combination chuck may be used also, as a universal chuck. Where only one chuck is provided for a lathe, the independent type is preferable. Setting the Work.-To set a piece of work in an independent chuck, first measure the piece at the points where the jaws are to grip it. The jaws are then moved out, leaving a distance between each pair large enough for the piece to slip between them, the jaws being kept centered by means of the guiding circles on the chuck face. The piece is placed in the jaws FIG. 13 and the latter are tightened down on it. If the piece is round, it can be centered by using a piece of chalk to locate the high spots in the usual way. If the piece is irregular, it is good practice to locate the desired center before chucking the piece, and this center can then be used as a guide in centering the work. If the work is heavy, so that it is likely to fall out of the chuck when the jaws are loosened, it can be held against the chuck by means of a block of wood placed between the work and the dead center, as in Fig. 13. If the work has a number of faces, as in the case of a cone pulley, it must be chucked so that the stock can be removed from each surface, and still be of the proper size. If a hole, cored very much to one side, is to be bored and set in the chuck so that the outside runs perfectly true, the cored hole will be so out of true that it cannot be finished. If the cored hole is set to run true, then the outside cannot be finished all over. In such a case, the work should be so set that both the outside and the cored hole run enough out of true to equalize the difference. Spring of Work From Pressure of Jaws.-When the work is light or frail, there is danger of springing under the pressure of the jaws. The jaws of the chuck should come against the more solid parts. For example, in chucking a pulley, it should be so set that the jaws come opposite the arms of the pulley. FIG. 14 Turning a Ring.-To turn a ring on the outside locate the jaws inside, as shown in Fig. 14. Before taking the finishing cut, the jaws should be loosened enough to release any spring of the piece where the pressure of the jaws was applied. The ring is then rechucked with the jaws bearing against the outer surface. To prevent injury to the finished surface, thin pieces of sheet copper, or tin are placed between the chuck After the ring is accurately centered, the inside is bored out to the desired size. The same precaution in regard to springing must be observed as when the outside was being turned. jaws and the work. Care of Chucks.-When a chuck is removed from the spindle, it is good practice to stuff the threaded hole with waste, and to place the chuck where it will be out of the way of chips and dirt from the machine. In replacing it on the spindle, both its threads and the threads on the spindle should be cleaned and oiled. It should be run on the spindle by pulling the belt by hand. the chuck on. The power of the lathe should never be utilized to run There is danger of injury to the operator, as well as trouble caused by the jamming of the chuck on the spindle. Never hammer the chuck or a piece of work in it, except, in the latter case, the light tapping re Pieces can be broken quired in centering the work. BO FIG. 15 When a face plate is not regularly provided with jaws, these can be improvised as in Fig. 15. They consist of L-shaped castings a bolted to the face plate and provided with setscrews. The shoulder below the point of the setscrew should be turned off so that the dimension b is the same on all of them. This will FIG. 16 FIG. 17 FIG. 18 enable the operator to place work against these shoulders during chucking. In Fig. 16 is shown a method of clamping a large flange to a face plate when it is desired only to bore the hole in the center |