The simplest thing to do on a lathe and one that will give the apprentice opportunity to become thoroughly familiar with all levers, etc., is turning a steel shaft. The various forms of lathe tools available and their method of use are fully described in Chapter XI (Lathe Tools, High-Speed Steel, Speeds And Feeds, Power For Cutting-Tools, Etc), while the forms of lathe dogs and proper use of centers are fully outlined in Chapter XIII (Lathe Work). The first thing to do is to provide centers in the shaft with a combined drill and center countersink in order to support it properly on the lathe centers.

The steps are first, to mark the end of the shaft which is done by scratching two lines at right angles. The point of intersection of the lines is where the center should be. To mark the place, a center punch is used as shown at Fig. 321-A. Place the shaft between the lathe centers after prick punching both ends and see if it runs true when revolved by hand. If it runs out hold a piece of chalk to the shaft while it turns and mark the high spots. Drive the center hole over in the direction necessary to have the shaft run true with center punch; in most cases it will mean moving the center nearer the high spot. The method of countersinking a shaft is shown at Fig. 321-B. A drill chuck is placed in the lathe spindle and fitted with a combined drill and countersink. Place one end of the shaft on the tail center and feed the bar in by turning the hand wheel at the end of the tail stock. Allow the countersink to feed in deep enough, then reverse the shaft and countersink the other end in the same manner. The countersink should be drilled deep enough so the point of the center will not be called upon to do any of the work of supporting the shaft. The countersink should have the same taper as the lathe center or 60 degrees, as fully outlined in a previous chapter.

Fig. 321.   Preliminary Steps to Turning and Facing Steel Shaft on the

Fig. 321. - Preliminary Steps to Turning and Facing Steel Shaft on the Lathe.

The shaft is then provided with a dog at one end that engages with a slot in the face plate to drive the piece and is supported by the tail stock center at the other end. Oil the centers well before starting to turn the lathe. The shaft should have a slight play between the centers in order that it turn easily. Select the proper tool (Chapter XI (Lathe Tools, High-Speed Steel, Speeds And Feeds, Power For Cutting-Tools, Etc)) for the character of the work and place it in the tool post, having the cutting point or edge as near the tool post as possible to prevent the tool springing under a heavy cut.

The position of a turning tool is very important when machining metal. At Fig. 321-C the usual position is shown. This is about 5 degrees measured on the circumference of the piece to be turned above the center line. If a tool is placed below center, it is apt to dig in.

The proper speed and feed to use is only determined by experience. It is best for the beginner to take light chips at the start. After the tool has been properly set, move the carriage over to the tail stock end of the bar and feed in the hand cross feed until the tool is slightly below the surface of the bar at one end. Set the lead screw gears for medium speed and feed the tool into the bar slowly by hand to make sure that the chip taken will not be too heavy for the lathe. After the chip is started, the automatic longitudinal feed may be locked in and the tool moved by power.

Before taking the final or finishing chips and polishing the shaft it will be well to face off the shaft end. This is done with a side tool as shown at Fig. 321-D. If the end of the shaft is very rough it may be better to face it off before starting to turn it down in order to secure an accurate cut. On reaching the countersink hole, the side tool may be fed in further to face the end of the shaft clean by slightly withdrawing the tail stock center.