Unit 2 • Workholding and Toolholding Devices for the Lathe 375 ed position. A screw on each side of the tailstock is secured to the workpiece (usually with a set screw). The to adjust its position. (See Figure 5.2.23.) dog is then engaged with the slot or lug of the drive plate Precise alignment can be done by mounting a test bar after capturing the work between the headstock and tail- etween the centers. Next, mount a dial indicator on the stock centers. Figure 5.2.26 shows some different types Dross slide or compound rest and preload the indicator trith contact against the side of the test bar near one end. Center the indicator contact on the diameter, not above or below. Then move the carriage near the other end of the est bar and adjust the tailstock adjustment screws until Ibe indicator readings are the same at each end of the test Bar. (See Figure 5.2.24.) Direct Mounting Work for Between-Centers Operations To prepare a workpiece for mounting between centers, Each end must first be drilled with a center drill (combina• tion drill and countersink) to accept the 60-degree points • the lathe centers. Center drilling can be performed on the lathe while holding the work in a chuck or collet. It :an also be performed on a drill press. Center drills have a small straight pilot followed by cutting edges that extend into a taper with a 60-degree included angle. It is impor• tant to center-drill to the proper depth when preparing ivork to be mounted between centers. (See Figure 5.2.25.) I NOTE: Before choosing to produce a part with this method, it must be acceptable per the drawing to produce center holes in either end. These holes are not allowable Dn some workpieces. Since the centers alone cannot provide sufficient torque to rotate a workpiece, two more accessories are needed. A drive plate is a specially designed plate that is mounted on the spindle nose. These drive plates usually feature a drive slot or a drive lug. Many faceplates can also be used as drive plates. A drive dog (or lathe dog) is FIGURE 5.2.26 (A) A bent tail lathe dog fits in the slot of a drive plate. (B) A straight tail lathe dog is driven by the lug on FIGURE 5.2.25 Center drill depth is important for accurate a drive plate. (C) A clamp-type lathe dog can be used for hold• mounting of work between centers. Hole A is too shallow. Hole B ing square workpieces between centers. is too deep. Hole C shows the proper depth. ©Cengage Learning 2012 All images ©Cengage Learning 2012 .